Aashto Caua 02

Specification for Bridge Design

Section 11 - Abutments, Piers and Walls

11.1. SCOPE

This section provides requirements for design of abutments and walls. Conventional retaining walls, anchored walls, mechanically stabilized earth (MSE) walls, and prefabricated modular walls are considered.

11.2. DEFINITIONS

Abutment - A structure that supports the end of a bridge span and provides lateral support for fill material on which the roadway rests immediately adjacent to the bridge.

Anchored Wall - An earth retaining system typically composed of the same elements as nongravity cantilevered walls that derive additional lateral resistance from one or more tiers of anchors.

Mechanically Stabilized Earth Wall - A soil-retaining system employing either strip or grid-type, or metallic or polymeric, tensile reinforcements in the soil mass and a facing element that is either vertical or nearly vertical.

Nongravity Cantilever Wall - A soil-retaining system that derives lateral resistance through embedment of vertical wall elements and support-retained soil with facing elements. Vertical wall elements may consist of discrete elements, e.g., piles, caissons, drilled shafts, or auger-cast piles spanned by a structural facing, e.g., lagging, panels, or shotcrete. Alternatively, the vertical wall elements and facing may be continuous, e.g., diaphragm wall panels, tangent piles, or tangent-drilled shafts.

Pier - That part of a bridge structure between the superstructure and the connection with the foundation.

Prefabricated Modular Wall - A soil-retaining system employing interlocking soil-filled reinforced concrete or steel modules or bins to resist earth pressures by acting as gravity-retaining walls.

Rigid Gravity and Semigravity Retaining Wall - A structure that provides lateral support for a mass of soil and that owes its stability primarily to its own weight and to the weight of any soil located directly above its base.

In practice, different types of rigid gravity and semigravity retaining walls may be used. These include:

A gravity wall depends entirely on the weight of the stone or concrete masonry and of any soil resting on the masonry for its stability. Only a nominal amount of steel is placed near the exposed faces to prevent surface cracking due to temperature changes.

A semigravity wall is somewhat more slender than a gravity wall and requires reinforcement consisting of vertical bars along the inner face and dowels continuing into the footing. It is provided with temperature steel near the exposed face.

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A cantilever wall consists of a concrete stem and a concrete base slab, both of which are relatively thin and fully reinforced to resist the moments and shears to which they are subjected.

A counterfort wall consists of a thin concrete face slab, usually vertical, supported at intervals on the inner side by vertical slabs or counterforts that meet the face slab at right angles. Both the face slab and the counterforts are connected to a base slab, and the space above the base slab and between the counterforts is backfilled with soil. All the slabs are fully reinforced.

A prefabricated modular wall consists of individual structural units assembled at the site into a series of hollow bottomless cells known as cribs. The cribs are filled with soil, and their stability depends not only on the weight of the units and their filling but also on the strength of the soil used for the filling. The units themselves may consist of reinforced concrete or fabricated metal.

11.3. NOTATION

Ab = surface area of transverse reinforcement in bearing (diameter times length) (mm2) (11.9.5.3)

Am = maximum wall acceleration coefficient at the centroid (11.9.6.1)

AReffi = area of reinforcement per vertical mm (mm2/mm) (11.9.6.2)

As = total surface area (top and bottom) of reinforcement beyond failure plane, less any sacrificial thickness (mm2) (11.9.5.3)

B = width of retaining wall foundation (mm) (11.9.7)

B’ = offective width of retaining wall foundation (mm) (C11.9.4.2).

b = width of bin module (mm) (11.10.4)

b/i = reinforcement width for layer i (mm) (11.9.6.2)

Co = uniaxial compressive strength of rock (MPa) (11.5.6)

D60/D10 = uniformity coefficient of soil defined as ration of particle size of soil thast is 60 percent finer in size to the particle size of soil that is 10 percent finer in size (C11.9.5.3)

d = fill above wall (mm) (11.9.7)

Ec = thickness of metal reinforcement at end of service life (mm) (11.9.8.1)

En = nominal thickness of steel reinforcement at construction (mm) (11.9.8.1)

Es = sacrificial thickness of metal expected to be lost by uniform corrosion during service life (mm) (11.9.8.1)

e = eccentrity of load from certerline of farndation (mm) (C11.9.4.2).

Fr = friction component of resultant on base of foundation (N/mm) (11.6.3.1)

fd = coefficient of resistance to direct sliding of reinforcement (11.9.5.3)

f* = apparent coefficient of friction at each reinforcement level (11.9.5.3)

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Hm = incremental dynamic inertia force at level i (N/mm of structure) (11.9.6.2)

H1 = equivalent wall height (mm) (11.9.5.2.2)

H2 = effective wall height (mm) (11.9.6.1)

hi = height of reinforced soil zone contributing horizontal load to reinforcement at level i (mm) (11.9.5.2.1)

i = inclination of ground slope behind face of wall (DEG) (11.9.5.2.2)

k = earth pressure coefficient (11.9.5.2.2)

ka = active earth pressure coefficient (11.9.4)

ko = at-rest earth pressure coefficient (11.9.5.2.2)

L = spacing between vertical elements or facing supports (mm) (11.8.5.2)

Lei = effective reinforcement length for layer i (mm) (11.9.6.2)

l = length of mat beyond failure plane (mm) (11.9.5.3)

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Is = point load strength index (MPa) (11.5.6)

Mmax = maximum bending moment in vertical wall element or facing (Nmm or Nmm/mm) (11.8.5.2)

N = normal component of resultant on base of foundation (N/mm) (11.6.3.1)

Ncorr = SPT blow count corrected for overburden pressure (Blows/300 mm) (11.8.4.2)

Np = passive resistance factor (11.9.5.3)

n = number of transverse bearing members behind failure plane (11.9.5.3)

Pa = resultant of active lateral earth pressure (N/mm) (11.6.3.1)

PAE = dynamic horizontal thrust (N/mm) (11.9.6.1)

Pb = pressure inside bin module (MPa) (11.10.4)

Pi = horizontal force per mm of wall transferred to soil reinforcement at level i (N/mm) (1.9.5.2.1)

PIR = horizontal inertial force (N/mm) (11.9.6.1)

Pfg = pullout capacity developed by passive resistance per grid (N) (11.9.5.3)

Pfs = pullout capacity per strip (N) (11.9.5.3)

Ph = horizontal component of lateral earth pressure (N/mm) (11.6.3.1)

PIR = horizontal inertia force (N/mm) (11.9.6.1)

Pis = internal inertia force (N/mm) (11.9.6.2)

Pv = vertical component of lateral earth pressure (N/mm) (11.6.3.1)

p = average lateral pressure, including earth, surcharge, and water pressure, acting on the section of wall element being considered (MPa) (11.8.5.2)

Qa = ultimate unit anchor resistance (N/mm) (11.8.4.2)

qmax = maximum unit soil pressure on base of foundation (MPa) (11.6.3.1)

Rn = nominal resistance (11.5.4)

RR = factored resistance (11.5.4)

SHi = horizontal reinforcement spacing for layer i (mm) (11.9.6.2)

SPT = standard penetration test (11.8.4.2)

T1 = limit state reinforcement tension (N) (11.9.5.1.3)

T5 = tensile load at which strain in polymeric soil reinforcement exceeds 5 percent (N) (11.9.5.1.3)

w = width of mat (mm) (11.9.5.3)

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x = spacing between vertical element supports (mm) (11.8.5.2)

y = distance above base of foundation to location of Ph (mm) (11.6.3.1)

Z = depth below effective top of wall or to reinforcement (mm) (11.9.5.3)

YP = load factor for earth pressure in Table 3.4.1-2 (11.9.5.2.2)

Ys = soil density (kg/m3) (11.9.5.3)

= wall - backfill interface friction argle (DEG) (C11.10.1)

= soil-reinforcement angle of friction (DEG) (11.9.5.3)

= resistance factor (11.5.4)

f = internal friction angle of foundation soil (DEG) (11.9.5.2.2)

= magnitude of lateral pressure due to surcharge (MPa) (11.9.5.2.1)

= maximum stress in soil reinforcement in abutment zones (11.9.7)

v = vertical stress in soil (MPa) (11.9.5.2.2)

V1 = vertical soil stress (MPa) (11.9.7)

V2 = vertical soil stress due to footing load (MPa) (11.9.7)

1.4. SOIL PROPERTIES AND MATERIALS

11.4.1. General

Where possible, backfill materials should be granular, free-draining materials. Where clayey soils are used as backfill, drainage shall be provided to reduce hydrostatic water pressure behind the wall.

11.4.2. Determination of Soil Properties

The provisions of Articles 2.4 and 10.4 shall apply.

11.5. LIMIT STATES AND RESISTANCE FACTORS

11.5.1. General

Design of abutments, piers, and walls shall satisfy the criteria for the service limit state specified in Article 11.5.2 and for the strength limit state specified in Article 11.5.3.

11.5.2. Service Limit States

Abutments, piers, and walls shall be investigated for excessive displacement at the service limit state.

11.5.3. Strength Limit State

Design of abutments and walls shall be investigated at the strength limit states using Equation 1.3.2.1-1 for:

Bearing resistance failure,

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Lateral sliding,

Excessive loss of base contact,

Overall instability,

Pull out failure of anchors or soil reinforcements, and

Structural failure.

11.5.4. Resistance Requirement

Abutments, piers, and retaining structures and their foundations and other supporting elements shall be proportioned by the appropriate methods specified in Articles 11.6, 11.7, 11.8, 11.9, or 11.10, so that their resistance satisfies Article 11.5.5.

The factored resistance, RR, calculated for each applicable limit state shall be the nominal resistance, Rn, multiplied by an appropriate resistance factor, , specified in Table 11.5.6-1.

11.5.5. Load Combinations and Load Factors

Abutments, piers, and retaining structures and their foundations and other supporting elements shall be proportioned for all applicable load combinations specified in Article 3.4.1.

11.5.6. Resistance Factors

Resistance factors for geotechnical design of foundations are specified in Tables 10.5.4-1 through 10.5.4-3 and Table 1, for which:

Factors for soft rock are applicable for rock characterized by a uniaxial compressive strength, C0, less than 7.0 MPa or a point load strength index, Is, less than 0.30 MPa;

Factors for permanent walls are applicable for walls that have a specified service life greater than 36 months, walls in a highly aggressive environment, or walls where the consequences of failure are serious;

Factors for temporary walls are applicable for walls that have a specified service life less than or equal to 36 months and walls in a nonaggressive environment, where the consequences of failure are not serious;

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Vertical elements, such as soldier piles, tangent piles, and slurry trench concrete walls, shall be treated as either shallow or deep foundations, as appropriate, for purposes of estimating bearing resistance, using procedures described in Sections 10.6,10.7, and 10.8.

If methods other than those given in Tables 10.5.4-1 through 10.5.4-3 and Table 1 are used to estimate the soil capacity, the performance factors chosen shall provide the same reliability as those given in these tables.

Table 11.5.6.1 - Resistance Factors for Retaining Walls

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11.5.7. Extreme Event Limit Stat

The applicable load combinations specified in Table 3.4.1-1 shall be investigated. Unless otherwise specified, all resistance factors shall be taken as 1.0 when investigating the extreme event limit state.

11.6. ABUTMENTS AND CONVENTIONAL RETAINING WALLS

11.6.1. General Considerations

11.6.1.1. Loading

Abutments and retaining walls shall be investigated for:

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Lateral earth and water pressures, including any live and dead load surcharge;

The weight of the wall;

Temperature and shrinkage deformation effects; and

Earthquake loads as specified herein, in Section 3, and elsewhere in these Specifications.

The provisions of Article 3.11.5 shall apply. For stability computations, the earth loads shall be multiplied by the maximum and/or minimum load factors given in Table 3.4.1-2, as appropriate.

11.6.1.2. Integral Abutments

Integral abutments shall be designed to resist and/or absorb creep, shrinkage, and thermal deformations of the superstructure.

11.6.1.3. Load Effects In Abutments

For computing load effects in abutments, the weight of filling material directly over an inclined or stepped rear face, or over the base of a reinforced concrete spread footing may be considered part of the effective weight of the abutment.

Where spread footings are used, the rear projection shall be designed as a cantilever supported at the abutment stem and loaded with the full weight of the superimposed material, unless a more exact method is used.

11.6.1.4. Wingwalls And Cantilever Walls

Wingwalls may be designed as monolithic with the abutments or as free standing, with an expansion joint separating them from abutment walls.

The wingwall lengths shall be computed using the required roadway slopes. Wingwalls shall be of sufficient length to retain the roadway embankment and to furnish protection against erosion.

The vertical stems of cantilever walls shall be designed as cantilevers supported at the base.

11.6.1.5. Expansion And Contraction Joints

Consideration shall be given to measures that will accommodate the contraction and expansion of concrete walls.

11.6.2. Movement at the Service Limit State

11.6.2.1. Abutments

The provisions of Articles 10.6.2.2.3, 10.7.2.3, and 10.8.2.3 shall apply as applicable.

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11.6.2.2. Conventional Retaining Wall

Criteria for tolerable movement criteria for retaining walls shall be developed based on the function and type of wall, anticipated service life, and consequences of unacceptable movements.

The provisions of Articles 10.6.2.2, 10.7.2.2, and 10.8.2.2 shall apply as applicable.

11.6.3. Bearing Resistance and Stability at the Strength Limit State

11.6.3.1. General

Abutments and retaining walls shall be proportioned to ensure stability against bearing capacity failure, overturning, and sliding. Where a wall is supported by clayey foundation, safety against deep-seated foundation failure shall also be investigated. Stability criteria for walls with respect to various modes of failure shall be as shown in Figures 1 through 3. Where the horizontal earth pressure is computed using the Coulomb theory, and where the horizontal earth pressure is not applied directly to the back of the wall, a vertical component load acting on the vertical plane extending upward from the heel shall be considered.

Figure 11.6.3.1-1 - Earth Loads and Stability Criteria for Walls with

Clayey Soils in the Backfill or Foundation (Duncan et al. 1990)

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Figure 11.6.3.1-2 - Earth Loads and Stability Criteria for Walls with Granular Backfills and Foundations on Sand and Gravel (Duncan 1990)

Figure 11.6.3.1-3 - Earth Loads and Stability Criteria for Walls with Granular Backfills and Foundations on Rock (Duncan 1990)

11.6.3.2. Bearing Resistance

Bearing resistance shall be investigated at the strength limit state, assuming the following soil pressure distributions:

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If the wall is supported by a soil foundation: a uniformly distributed pressure over the effective base area, as shown in Figures 11.6.3.1-1 and 11.6.3.1-2.

If the wall is supported by a rock foundation: a linearly varying distribution of pressure over the effective base area, as shown in Figure 11.6.3.1-3.

11.6.3.3. Overturning

For foundations on soil, the location of the resultant of the reaction forces shall be within the middle one-half of the base.

For foundations on rock, the location of the resultant of the reaction forces shall be within the middle three-fourths of the base.

11.6.3.4. Overall Stability

The overall stability of the retaining wall, retained slope and foundation soil or rock shall be evaluated for all walls using limiting equilibrium methods of analysis. Special exploration, testing, and analyses may be required for bridge abutments or retaining walls constructed over soft deposits.

11.6.3.5. Subsurface Erosion

For walls constructed along rivers and streams, scour of foundation materials shall be evaluated during design, as specified in Article 2.6.4.4.2. Where potential problem conditions are anticipated, adequate protective measures shall be incorporated in the design.

The provisions of Article 10.6.1.2 shall apply. The hydraulic gradient shall not exceed:

For silts and cohesive soils: 0.20

For other cohesionless soils: 0.30

Where water seeps beneath a wall, the effects of uplift and seepage forces on active and passive ground pressures shall be considered.

11.6.3.6. Passive Resistance

Passive resistance shall be neglected in stability computations, unless the base of the wall extends below the depth of maximum scour, or other disturbances. In the latter case only, embedment below the greater of these depths may be considered effective.

Where passive resistance is utilized to ensure adequate wall stability, the calculated passive resistance of soil in front of abutments and conventional walls shall be sufficient to prevent unacceptable forward movement of the wall.

The passive resistance should be neglected if the soil providing passive resistance is soft, loose, or disturbed or if the contact between the soil and wall is not tight.

11.6.3.7. Sliding

The provisions of Article 10.6.3.3 shall apply.

11.6.4. Safety Against Structural Failure

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The structural design of individual wall elements and wall foundations shall comply with the provisions of Sections 5 and 6.

The provisions of Article 10.6.3.1.5 shall be used to determine the distribution of contact pressure for structural design of footings.

11.6.5. Seismic Design Provisions

The effect of earthquake shall be investigated using the extreme event limit state of Table 3.4.1-1 with resistance factors = 1.0 and an accepted methodology. This provision should only be applied to multispan bridges.

For foundations on soil, the location of the resultant of the reaction forces shall be within the middle 0.4 of the base.

For foundations on rock, the location of the resultant of the reaction forces shall be within the middle 0.6 of the base.

11.6.6. Drainage

Backfills behind abutments and retaining walls shall be drained or, if drainage cannot be provided, the abutment or wall shall be designed for loads resulting from earth pressure, plus full hydrostatic pressure resulting from water in the backfill.

11.7. PIERS

Piers shall be designed to transmit the loads on the superstructure and the loads on the pier itself to the foundation. The loads and load combinations shall be as specified in Section 3.

The structural design of piers shall be in accordance with the provisions of Sections 5 and 6 as appropriate.

11.8. ANCHORED WALLS

11.8.1. General

Anchored walls, illustrated in Figure 1, may be considered for both temporary and permanent support of stable and unstable soil and rock masses.

The feasibility of using an anchored wall at a particular location should be based on the suitability of subsurface soil and rock conditions within the bonded anchor stressing zone.

Where fill is placed behind a wall, either around or above the unbonded length, special designs and construction specifications shall be provided to prevent anchor damage.

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Figure 11.8.1-1 - Anchored Wall Nomenclature and Anchor Embedment Guidelines

11.8.2. Loading

The provisions of Article 11.6.1.1 shall apply, except that shrinkage and temperature effects need not be considered.

11.8.3. Movement Under the Service Limit State

The provisions of Articles 10.6.2, 10.7.2, and 10.8.2 shall apply.

The effects of wall movements on adjacent facilities shall be considered in the development of the design earth pressure in accordance with the provisions of Article 3.11.5.6.

11.8.4. Safety Against Soil Failure


The provisions of Articles 10.6.3, 10.7.3, and 10.8.3 shall apply.

Loads at the base of vertical wall elements shall be determined assuming that all vertical components of loads are transferred to the base of the elements. Side friction of wall elements shall not be included in the resistance to vertical loads

11.8.4.2. Anchor Pullout Capacity

Prestressed anchors shall be designed to resist pullout of the bonded length in soil or rock. The resistance of straight shaft anchors installed in small-diameter holes using a low grout pressure, may either be based on the results of anchor pullout load tests or estimated using Tables 1 and 2, where SPT values are corrected for overburden pressures.

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Other anchor types and installation procedures may require in-situ testing to determine suitable design values.

Table 11.8.4.2-1 - Ultimate Unit Resistance of Anchors in Soil

Table 11.8.4.2-2 - Ultimate Unit Resistance of Anchors in Rock

The anchor load shall be developed by suitable embedment outside of the critical failure surface in the retained soil mass.

Determination of the unbonded anchor length, inclination, and overburden cover shall consider:

The location of the critical failure surface furthest from the wall;

The minimum length required to ensure minimal loss of anchor prestress due to long-term ground movements;

The depth to adequate anchoring strata, as indicated in Figure 11.8.1-1; and

The method of anchor installation and grouting.

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The minimum horizontal spacing of anchors should be the larger of three times the diameter of the bonded zone or 1500 mm. If smaller spacings are required to develop the required load, consideration may be given to differing anchor inclinations between alternating anchors.



11.8.4.4. Passive Resistance

The provisions of Articles 11.6.3.6 and 11.6.3.7 shall apply.


11.8.5.1. Anchors

The horizontal component of anchor force shall be computed using the earth pressure distributions specified in Article 3.11 and any other horizontal pressure components acting on the wall. The total anchor force shall be determined on the basis of the anchor inclination. The horizontal anchor spacing and anchor capacity shall be selected to provide the required total anchor force.

11.8.5.2. Vertical Wall Elements

Discrete vertical wall elements shall be designed to resist all horizontal earth pressure, surcharge, water pressure, anchor, and seismic loadings as well as the vertical component of the anchor loads and any other vertical loads. Horizontal supports may be assumed at each anchor location and at the bottom of the excavation if the vertical element is sufficiently embedded below the bottom of the excavation.

11.8.5.3. Facing

The maximum spacing between discrete vertical wall elements shall be determined on the basis of relative stiffness of the vertical elements and facing, and the type and condition of soil to be supported. Facing may be designed assuming simple support between elements, with or without soil arching, or assuming continuous support over several anchors.


The provisions of Article 11.6.5 shall apply.

11.8.7. Corrosion Protection

Prestressed anchors and anchor heads shall be protected against corrosion consistent with the ground and groundwater conditions at the site. The level and extent of corrosion protection shall be a function of the ground environment and the potential consequences of an anchor failure. Corrosion protection shall be applied in accordance with the provisions of the Construction Specification, Section 806, Ground Anchors.

11.8.8. Anchor Stressing and Testing

All production anchors shall be subjected to load testing and stressing in accordance with the provisions of AASHTO LRFD Bridge Construction Specifications, Article 6.5.5, Testing and Stressing. Preproduction load tests may be specified when unusual conditions are encountered to

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verify safety with respect to the design load or to establish the ultimate anchor load or the load at which excessive creep occurs.

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11.8.9. Drainage

Seepage shall be controlled by installation of a drainage system behind the facing with outlets at or near the base of the wall. Drainage panels shall be designed and detailed to maintain their drainage characteristics under the design earth pressures and surcharge loadings and shall extend from the base of the wall to a level 300 mm below the top of the wall.

11.9. MECHANICALLY STABILIZED EARTH WALLS

11.9.1. General

MSE walls may be considered where conventional gravity, cantilever, or counterforted concrete retaining walls are considered, and particularly where substantial total and differential settlements are anticipated.

MSE walls shall not be used under the following conditions:

Where utilities other than highway drainage are to be constructed within the reinforced zone, or

Where floodplain erosion or scour may undermine the reinforced fill zone or any supporting footing, or

With galvanized metallic reinforcements exposed to surface or groundwater contaminated by acid mine drainage or other industrial pollutants as indicated by low pH and high chlorides and sulfates.

The size of the reinforced earth mass shall be determined on the basis of:

The requirements for stability and geotechnical strength, as specified in Article 11.9.4 for gravity walls;

The requirements for the structural resistance within the reinforced soil mass itself, as specified in Article 11.9.5, for the panel units and for the development of reinforcement beyond assumed failure zones; and

Traditional requirements for reinforcement length not less than 70 percent of the wall height or 2400 mm as specified in Article 11.9.5.1.4.

11.9.2. Loading


11.9.3. Movement Under Service Limit State

The provisions of Article 11.6.2 shall apply as applicable.

For systems with panel areas less than 2.8 x 106 mm2 and with a maximum joint width of 19 mm, the maximum slope resulting from calculated differential settlement shall be taken as given in Table 1.

Where foundation conditions indicate large differential settlements over a short horizontal distance, a vertical full-height slip joint shall be provided.

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Table 11.9.3-1 - Relationship Between Joint Width and Limiting Distortion of the Face of MSE Walls


Safety against soil failure shall be evaluated by assuming the reinforced soil mass to be a rigid body. The coefficient of active earth pressure, Ka, used to compute the earth pressure of the random backfill on the back of the reinforced soil mass shall be determined using the friction angle of the random backfill. In the absence of specific data, a maximum friction angle of 30o may be used.

11.9.4.1. Sliding


The coefficient of sliding friction at the base of the reinforced soil mass shall be determined using the friction angle of the foundation soil. In the absence of specific data, a maximum friction angle of 30 o

may be used.


For the purpose of computing strength bearing capacity, an equivalent footing shall be assumed whose length is the length of the wall, and whose width is the length of the reinforcement strip at the foundation level. Bearing pressures shall be computed using a uniform base pressure distribution over an effective width of footing determined in accordance with the provisions of Articles 10.6.3.1 and 10.6.3.2.






11.9.5.1. Structure Dimensions

11.9.5.1.1. General

A preliminary estimate of the structural size of the stabilized soil mass may be determined on the basis of reinforcement pullout beyond the failure zone, for which resistance is specified in Article 11.9.5.3.

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11.9.5.1.2. Steel Reinforcements in Soil

Transverse and horizontal elements of reinforcing grid shall be of the same size.

The horizontal force used to design the connections to the panels may be taken as not less than 85 percent of the maximum calculated force, determined as specified in Article 11.9.5.2.2 or 11.9.5.2.3, except for the lower one-half of the structure, where it shall be 100 percent of the maximum calculated force.

11.9.5.1.3. Polymeric Reinforcements in Soil

The long-term stress-strain-time behavior of polymeric reinforcement shall be determined from results of controlled laboratory creep tests conducted for a minimum duration of 10 000 hours for a range of load levels on samples of the finished product in accordance with ASTM D 5262. Samples shall be tested in the direction in which the load will be applied. Results may be extrapolated to the required design life using procedures outlined in ASTM D 2837.

The reinforcement tensile strength shall be the lesser of:

T1 - the highest load level at which the log-time-creep strain-rate continues to decrease with time within the required lifetime and no failure either brittle or ductile can occur, or

T5 - the tension level at which total strain is not expected to exceed 5 percent within the design lifetime.

The effects of aging, chemical, and biological exposure, environmental stress cracking, stress relaxation, hydrolysis, and variations in the manufacturing process as well as the effects of construction damage shall be evaluated and extrapolated to the required design life.

11.9.5.1.4. Minimum Length of Soil Reinforcement

For both strip- and grid-type reinforcement, the minimum soil reinforcement length should be taken as the greater of 70 percent of the wall height as measured from the leveling pad or 2400 mm. Reinforcement length shall be increased for surcharges and other external loads.

The reinforcement length shall be uniform throughout the entire height of the wall, unless substantiating evidence is presented to indicate that variation in length is satisfactory.

11.9.5.1.5. Minimum Front Face Embedment

Unless constructed on rock foundations, the embedment at the front face of the wall in mm shall not be less than:

The value specified in Table 1, in which H is the height of structure above the top of the leveling pad in mm;

A depth based on the external stability requirement; and

600 mm.

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Table 11.9.5.1.5-1 - Minimum Front Face Embedment

A minimum horizontal bench width of 1200 mm shall be provided in front of walls founded on slopes.

11.9.5.1.6. Panels

Panels shall be designed to resist the horizontal force in the soil reinforcements at the reinforcement to panel connection, as specified in Articles 11.9.5.1.2 and 11.9.5.2. The tension in the reinforcement may be assumed to be resisted by a uniformly distributed earth pressure on the back of the panel.

The minimum panel thickness at and in the vicinity of embedded connections shall be 140 mm and 90 mm elsewhere. The minimum concrete cover shall be 38 mm. Reinforcement shall be provided to resist the average loading conditions for each panel. Temperature and shrinkage steel shall be provided as specified in Article 5.10.8. Epoxy-coated reinforcement shall be considered where salt spray is anticipated.

11.9.5.2. Internal Stability

11.9.5.2.1. General

MSE walls shall be evaluated for internal failure by slip or rupture of the reinforcements.

The factored horizontal force acting on the reinforcement at any reinforcement level, Pi, shall be:

Pi = (11.9.5.2.1-1)

where:

hi = height of reinforced soil zone contributing horizontal load to the reinforcement at level determined as the vertical distance from the midpoint between layer i and the next overlying layer to the midpoint between layer i and the next underlying layer (mm)

= factored horizontal stress at layer i, determined in accordance with Article 11.9.5.2.2 or Article 11.9.5.2.3 (MPa)

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11.9.5.2.2. Inextensible Reinforcements

Internal stability of structures constructed with metallic strip or grid reinforcements shall be analyzed by considering that the in-situ reinforced zone is divided into two zones: the active zone and resistant zone.

The failure surface shall be assumed to be as specified in Figure 1.

The factored horizontal stress, H, at each reinforcement level shall be:

H = YP vk (11.9.5.2.2-1)

where:

YP = the load factor for earth pressure in Table 3.4.1-2

k = horizontal pressure coefficient given below

= pressure due to resultant vertical forces at reinforcement level being evaluated, determined using a uniform pressure distribution over an effective width (L-2e) as specified in Article 10.6.3.1.5 (MPa)

The vertical effective stress, , at each level of reinforcement shall consider the local equilibrium of all forces at that level only.

Structures shall be designed using k = k0 at H1 above the top of the leveling pad and decreasing linearly to k = ka at 6000 mm as shown in Figure 1. Below a 6000 mm depth, k = ka shall be used. The earth pressure coefficients of ka and ko shall be assumed to remain the same, regardless of the external loading conditions. The values of ka and ko shall be taken from Article 3.11.5.7, with taken as the friction angle of reinforced soil zone. Alternatively, the horizontal stresses at each reinforcing level may be computed using structure stiffness concepts.

The maximum friction angle used for the determination of horizontal force within the reinforced soil zone shall be taken as 34o, unless the specific project select backfill is tested for frictional strength by triaxial or direct shear testing methods, ASTM D 2850 and AASHTO T 236 (ASTM D 3080), respectively. Live loads shall be positioned for extreme force effect within the physical zone available to live loads. The provisions of Article 3.11.6 shall apply.

846


Figure 11.9.5.2.2-1 - Determination of Failure Plane and Earth Pressure Coefficients MSE Wall with Inextensible Reinforcements

11.9.5.2.3. Extensible Reinforcements

Internal stability for structures constructed with polymeric reinforcements shall be analyzed using a tieback wedge method approach. A failure plane may be assumed to be defined by the Rankine active earth pressure zone, which is defined by a straight line passing through the wall toe and oriented at an angle of 450 + /2 from the horizontal, for both horizontal and sloping backfill conditions. The Rankine pressure distribution may be determined as specified in Article 3.11.5.7.

Reinforcement shall be designed to resist hydrostatic pressure and the active pressure on a panel resulting from all applied vertical loads.

The value of ka in the reinforced soil zone shall be assumed to be independent of all external loads, except sloping fills. The maximum friction angle provisions of Article 11.9.5.2.2 shall apply.

Where site-specific tests are performed, the soil strength shall be evaluated at residual stress levels.

11.9.5.3. Pullout Design Parameters

847


The pullout resistance shall be investigated at each level. Only the effective pullout length that extends beyond the theoretical failure surfaces shall be used in this investigation.

The minimum length in the resistant zone shall be 900 mm. The reinforcement length at all levels shall be equal. Minimum total length shall be 2400 mm.

The ultimate pullout capacity of ribbed or smooth steel reinforcing strips, Pfs, shall be taken as:

Pfs = gf*YsZAs x 10-9 (11.9.5.3-1)

where:

g = acceleration of gravity (m/s2)

f* = apparent coefficient of friction at each reinforcement level

As = total top and bottom surface area of reinforcement along the effective pullout length beyond the failure plane specified in Figure 1, less any sacrificial thickness (mm2)

Z = depth below effective top of wall or to reinforcement (mm)

Ys = unfactored soil density (kg/m3)

In the absence of pullout test data for ribbed reinforcing strips in backfill materials conforming to the Construction Specification, Section 807, a maximum value of the apparent coefficient of friction, f *, of 2.0 or less shall be taken at ground level, and may be assumed to decrease linearly to a value equal to tg , at a depth of 6000 mm, where is the friction angle of the backfill within the reinforced volume.

For smooth steel reinforcing strips, the apparent coefficient of friction shall be constant at all depths and may be taken as:

f* = tg 0.4 (11.9.5.3-2)

where:

= soil-reinforcement angle of friction (DEG)

For steel grid reinforcing systems with transverse bar spacings of 150 mm or greater, the generalized relation for ultimate pullout capacity, Pfg , shall be taken as:

Pfg = g Np Ys Zn Ab x 10-9 (11.9.5.3-3)

where:


Np = passive resistance factor taken either from backfill specific pullout tests or in lieu of such test data, as a function of depth as specified in Figure 1


848



n = number of transverse bearing members behind failure plane

Ab = surface area of transverse reinforcement in bearing, less any sacrificial thickness of cross bars (diameter times length) (mm2)

Figure 11.9.5.3-1 - Pullout Factors for Inextensible Mesh and Grid Reinforcement

For steel grid reinforcements with transverse spacing less than 150 mm, the ultimate pullout capacity, Pfg, shall be taken as:

Pfg = 2 gwl Ys Zfd tan x 10-9 (11.9.5.3-4)

where:


w = width of mat (mm)

I = length of mat beyond failure plane (mm)



fd = coefficient of resistance to direct sliding of reinforcement

= internal friction angle of the reinforced soil zone (DEG)

849


The value of fd may be assumed to vary from 0.45 for continuous sheets to 0.8 for bar mats with transverse spacing of 150 mm. The values of fd must be determined experimentally for each grid geometry.

For polymeric reinforcement, Equation 4 is applicable where fd is developed for a range of normal stresses in accordance with Geosynthetic Research Institute Test Method GG-5. The coefficient f d, obtained experimentally, may be limited by the Limit State Tensile Load, T1, for the product as specified in Article 11.9.5.1.3.


11.9.6.1. External Stability

Stability determinations shall be made by considering static forces; the horizontal inertial force, P IR, and 50 percent of the dynamic horizontal thrust, PAE. The dynamic horizontal thrust, PAE, shall be evaluated using the pseudo-static Mononobe-Okabe method and shall be applied to the back surface of the reinforced fill at the height of 0.6H from the base and the horizontal inertial force at the midheight of the structure. Values of PAE and PIR for structures with horizontal backfill may be determined using the following:

Am = (1.45 - A) A (11.9.6.1-1)

PAE = 0.375Amg Ys H2 x 10-9 (11.9.6.1-2)

PIR = 0.5 Amg Ys H2 x 10-9 (11.9.6.1-3)

where:

A = maximum earthquake acceleration

Am = maximum wall acceleration coefficient at the centroid


Ys = soil density (kg/m3)

H = height of wall (mm)

For structures with sloping backfills, the inertial force, PIR, shall be based on an effective mass having a height H2 and a base width equal to 0.5 H2 determined as follows:

H2 = H + (11.9.6.1-4)

where:

i = slope of backfill (DEG)

The inertia force shall be taken to act simultaneously with one-half the dynamic horizontal thrust, P AE, computed using the pseudo-static Mononobe-Okabe method and applied at 0.6 H2 above the base on the back surface of the effective mass.

11.9.6.2. Internal Stability

850


Reinforcements shall be designed to withstand horizontal forces generated by the internal inertia force, Pis and the static forces. The total inertia force, P is, per unit length of structure shall be considered equal to the mass of the active zone times the maximum wall acceleration coefficient A m. This inertial force shall be distributed to the reinforcements proportionally to their resistant areas as follows:

851


Hm = Pis (11.9.6.2-1)

for which:

AReffi = (11.9.6.2-2)

where:

Hm = incremental dynamic inertia force at Level i (N/mm of structure)

Pis = internal inertia force (N/mm)

bi/ = reinforcement width for layer i (mm)

Lei = effective reinforcement length for layer i (mm)

SHi = horizontal reinforcement spacing for layer i (mm)

For seismic loading conditions, values of resistance factors applicable to f*, NP, and fd, specified in Article 11.9.5.3, should be reduced to 80 percent of the values specified in Article 11.5.6.

11.9.7. MSE Abutments

Abutment footings shall be proportioned to meet the sliding and overturning criteria specified in Articles 11.9.4.1 and 11.9.4.3, respectively. They shall also be proportioned for maximum uniform bearing pressures using an effective width of foundation (L - 2e) as specified in Article 10.6.3.1.5.

The MSE wall below the abutment footing shall be designed for the additional loads imposed by the footing pressure and supplemental earth pressures resulting from horizontal loads applied at the bridge seat and from the backwall. The footing load may be assumed to be uniformly distributed over the effective width of foundation (L - 2e) at the base of the footing and to be dispersed with depth, using a slope of 2.0 vertical to 1.0 horizontal. The supplemental horizontal loads may be applied as shears along the bottom of the footing, uniformly diminishing with depth to a point on the face of the wall equal to twice the effective width of the abutment footing.

The factored horizontal force acting on the reinforcement at any reinforcement level, P i, shall be taken as:

Pi = Hmax hi (11.9.7-1)

where:

Hmax = factored horizontal stress at layer i, as defined by Equation 2 (MPa)

hi = height of reinforced soil zone contributing horizontal load to the reinforcement at level i computed as the vertical distance from the midpoint between layer i and the next overlying layer to the midpoint between layer i and the next underlying layer (mm)

852


Horizontal stresses in abutment reinforced zones shall be determined by superposition as follows and as specified in Figure 1:

Hmax = Yp ( v1k + v2ka + H) (11.9.7-2)

where:

Yp = load factor for earth pressure in Table 3.4.1-2

H = magnitude of lateral pressure due to surcharge (MPa)

v1 = vertical soil stress (MPa)

v2 = vertical soil stress due to footing load (MPa)

k = earth pressure coefficient varying between ko and ka as specified in Figure 11.9.5.2.2-1

ko = at-rest earth pressure coefficient specified Article 3.11.5.7

ka = active earth pressure coefficient specified Article 3.11.5.7

The effective length used for calculations of internal stability under the abutment footing shall be the lesser of the length beyond the end of the footing or the length beyond a distance from the facing equal to 30 percent of (H + d), where H and d shall be taken as shown in Figure 1.

The minimum distance from the centerline of the bearing on the abutment to the outer edge of the facing shall be 1000 mm. The minimum distance between the back face of the panel and the footing shall be 150 mm.

The provisions of Article 10.6.2.2 shall apply as applicable.

For structures supporting bridge abutments, the maximum horizontal force shall be used for design of the connection between the panel and reinforcement throughout the height of the structure.

The density, length, and cross-section of the soil reinforcements designed for support of the abutment wall shall be carried on the wingwalls for a minimum horizontal distance equal to 50 percent of the height of the abutment wall.

In pile-supported abutments, the horizontal forces transmitted to the piles shall be resisted by the lateral capacity of the piles, by additional reinforcements to tie the pile cap into the soil mass, or by batter piles. The facing shall be isolated from horizontal loads associated with lateral pile deflections. A minimum clear distance of 450 mm shall be provided between the facing and piles. Piles shall be specified to be driven prior to wall construction and cased through the fill if necessary.

The equilibrium of the system should be checked at each level of reinforcement below the bridge seat. Due to the relatively high bearing pressures near the panel connections, the adequacy and ultimate capacity of panel connections should be determined by conducting pullout and flexural tests on full-sized panels.

853


Figure 11.9.7-1 - Horizontal Stresses in Abutments

11.9.8. Design Life Considerations

11.9.8.1. Steel Reinforcement

The structural design of galvanized steel soil reinforcements and connections shall be made on the basis of a thickness, Ec, as follows:

Ec = En - Es (11.9.8.1-1)

where:

Ec = thickness of metal reinforcement at end of service life (mm)

En = nominal thickness of steel reinforcement at construction (mm)

Es = sacrificial thickness of metal expected to be lost by uniform corrosion during service life of structure (mm)

854


For structural design, sacrificial thicknesses shall be computed for each exposed surface as follows:

Loss of galvanizing = 0.015 mm/year for first 2 years

= 0.004 mm/year for subsequent years

Loss of carbon steel = 0.012 mm/year after zinc depletion

Other corrosion-resistant coatings, if specified, shall be the electrostatically applied, resin-bonded, epoxy type, with minimum application thicknesses of 0.40 mm in conformance with the requirements of AASHTO M284M.

11.9.8.2. Polymeric Reinforcement

The provisions of Article 11.9.5.1.3 shall apply.

11.9.9. Drainage

Internal drainage measures shall be considered for all structures to prevent saturation of the reinforced backfill and to intercept any surface flows containing aggressive elements.

MSE walls in cut areas and side-hill fills with estabIished groundwater levels shall be constructed with drainage blankets in back of and beneath the reinforced zone.

11.9.10. Subsurface Erosion


11.9.11. Special Loading Conditions

For internal design, concentrated vertical line loads may be assumed to disperse uniformly with depth in the reinforced soil mass using a slope of 2.0 vertical to 1.0 horizontal.

Traffic loads shall be considered in accordance with the provisions of Article 3.11.6.2.

For structures along rivers and streams, a minimum differential hydrostatic pressure equal to 900 mm of water shall be considered for design. This load shall be applied at the high-water level. Effective unit weights shall be used in the calculations for internal and external stability beginning at levels just below the application of the differential hydrostatic pressure.

Parapets and traffic barriers shall satisfy crash testing requirements as specified in Section 13.

11.10. PREFABRICATED MODULAR WALLS

Prefabricated modular systems may be considered where conventional gravity, cantilever, or counterfort concrete retaining walls are considered.

Prefabricated modular wall systems shall not be used under the following conditions:

On curves with a radius of less than 240 000 mm, unless the curve can be substituted by a series of chords.

855


Steel modular systems shall not be used where the groundwater or surface runoff is contaminated with acid.

11.10.1. Loading


Where the back of the prefabricated modules forms an irregular, stepped surface, the earth pressure shall be computed on a plane surface drawn from the upper back corner of the top module to the lower back heel of the bottom module.

The value of ka, used to compute lateral thrust resulting from random backfill and other loads behind the wall, shall be computed on the basis of the friction angle of the backfill behind the modules. If sufficient amounts of structural backfill are used behind the prefabricated modules, a value of 34 0 may be used for . In the absence of specific data, a maximum friction angle of 30o shall be used.

11.10.2. Movement Under the Service Limit State

The provisions of Article 11.6.2 shall apply as applicable.

Calculated longitudinal differential settlements along the face of the wall shall result in a slope less than 1/200.


11.10.3.1. General

For sliding and overturning stability, the system shall be assumed to act as a rigid body. Determination of stability shall be made at every module level.

Passive pressures shall be neglected in stability computations, unless the base of the wall extends below the depth of maximum scour, or other disturbance. For these cases only, the embedment below the greater of these depths may be considered effective in providing passive resistance.

11.10.3.2. Sliding


Computations for sliding stability may consider that the friction between the soil-fill and the foundation soil, and the friction between the bottom modules or footing and the foundation soil are effective in resisting sliding. The coefficient of sliding friction between the soil-fill and foundation soil at the wall base shall be the lesser of of the soil fill and of the foundation soil. The coefficient of sliding friction between the bottom modules or footing and the foundation soil at the wall base shall be reduced, as necessary, to account for any smooth contact areas.

In the absence of specific data, a maximum friction angle of 30o shall be used for .

856


Figure 11.10.3.2-1 - Prefabricated Modular Walls - Continuous Pressure Surfaces

857


Figure 11.10.3.2-2 - Prefabricated Modular Walls - Irregular Pressure Surfaces



858


Bearing resistance shall be computed by assuming that dead loads and earth pressure loads are resisted by point supports per unit length at the rear and front of the modules or at the location of the bottom legs. A minimum of 80 percent of the soil weight inside the modules shall be considered to be transferred to the front and rear support points. If foundation conditions require a footing under the total area of the module, all of the soil weight inside the modules shall be considered.



A maximum of 80 percent of the soil-fill inside the modules is effective in resisting overturning moments.

11.10.3.5. Subsurface Erosion

Bin walls may be used in scour-sensitive areas only where their suitability has been documented to the satisfaction of the Owner.



11.10.3.7. Passive Resistance And Sliding

The provisions of Articles 10.6.3.3 and 11.6.3.6 shall apply, as applicable.


Prefabricated modular units shall be designed for the factored earth pressures behind the wall and for factored pressures developed inside the modules. Rear face surfaces shall be designed for the factored earth pressures developed inside the modules during construction and for the difference between the factored earth pressures behind and inside the modules after construction. Strength and reinforcement requirements for concrete modules shall be in accordance with Section 5.

Strength requirements for steel modules shall be in accordance with Section 6. The net section used for design shall be reduced in accordance with Article 11.9.8.1.

Factored bin pressures shall be the same for each module and shall not be less than:

Pb = gYYsb x 10-9 (11.10.4-1)

where:

Pb = factored pressure inside bin module (MPa)


Ys = soil density (kg/m3)

Y = load factor specified in Table 3.4.1-2

b = width of bin module (mm)

859


Steel reinforcing shall be symmetrical on both faces unless positive identification of each face can be ensured to preclude reversal of units. Corners shall be adequately reinforced.

11.10.5. Abutments

Abutment seats constructed on modular units shall be designed by considering earth pressures and supplemental horizontal pressures from the abutment seat beam and earth pressures on the backwall. The top module shall be proportioned to be stable under the combined actions of normal and supplementary earth pressures. The minimum width of the top module shall be 1800 mm. The centerline of bearing shall be located a minimum of 600 mm from the outside face of the top precast module.

The abutment beam seat shall be supported by and cast integrally with the top module. The front face thickness of the top module shall be designed for bending forces developed by supplemental earth pressures. Abutment beam-seat loadings shall be carried to the foundation level and shall be considered in the design of footings.

Differential settlement provisions, specified in Article 11.9.3, shall apply.

11.10.6. Drainage

In cut and side-hill fill areas, prefabricated modular units shall be designed with a continuous subsurface drain placed at or near the footing grade and outletted as required. In cut and side-hill fill areas with established or potential groundwater levels above the footing grade, a continuous drainage blanket shall be provided and connected to the longitudinal drain system.

For systems with open front faces, a surface drainage system shall be provided above the top of the wall.

860


Section 12 - Buried Structures and Tunnel Liners

12.1. SCOPE

This section provides requirements for the selection of structural properties and dimensions of buried structures, e.g., culverts, and steel plate used to support tunnel excavations in soil.

Buried structure systems considered herein are metal pipe, structural plate pipe, long-span structural plate, structural plate box, reinforced concrete pipe, reinforced concrete cast-in-place and precast arch, box and elliptical structures, and thermoplastic pipe.

The type of liner plate considered is cold-formed steel panels.

12.2. DEFINITIONS

Abrasion - Loss of section or coating of a culvert by the mechanical action of water conveying suspended bed load of sand, gravel, and cobble-size particles at high velocities with appreciable turbulence.

Buried Structure - A generic term for a structure built by embankment or trench methods.

Corrosion - Loss of section or coating of a buried structure by chemical and/or electrochemical processes.

Culvert - A curved or rectangular buried conduit for conveyance of water, vehicles, utilities, or pedestrians.

FEM - Finite Element Method

Narrow Trench Width - The outside span of rigid pipe, plus 300 mm.

Projection Ratio - Ratio of the vertical distance between the outside top of the pipe and the ground or bedding surface to the outside vertical height of the pipe, applicable to reinforced concrete pipe only.

Soil Envelope - Zone of controlled soil backfill around culvert structure required to ensure anticipated performance based on soil-structure interaction considerations.

Soil-Structure Interaction System - A buried structure whose structural behavior is influenced by interaction with the soil envelope.

861


Tunnel - A horizontal or near horizontal opening in soil excavated to a predesigned geometry by tunneling methods exclusive of cut-and-cover methods.

12.3. NOTATION

A = wall area (mm2/mm); constant corresponding to the shape of the pipe (12.7.2.3)

AL = sum of all axle loads in an axle group (KIP); total axle load on single axle or tandem axles (N) (12.9.4.2) (12.9.4.3)

862


Asmax = maximum flexural reinforcement area without stirrups (mm2/mm) (12.1 0.4.2.4c)

AT = area of the top portion of the structure above the springline (mm2) (12.8.4.2)

Avr = stirrup reinforcement area to resist radial tension forces on cross-section width in each line of stirrups at circumferential spacing s (mm2/mm) (12.10.4.2.6)

Avs = required area of stirrups for shear reinforcement (mm2/mm) (12.10.4.2.6)

Bc = outside diameter or width of the structure (mm) (12.6.6.3)

B/c = out-to-out vertical rise of pipe (mm) (12.6.6.3)

Bd = horizontal width of trench at top of pipe (mm) (12.10.2.1.2)

BFE = earth load bedding factor (12.10.4.3.1)

BFLL = live load bedding factor (12.10.4.3.1)

CA = constant corresponding to the shape of the pipe (12.l0.4.3.2a)

Cc = load coefficient for positive pipe projection (12.l0.4.3.2a)

Cd = load coefficient for trench installation (12.10.2.1.2)

Cdt = load coefficient for tunnel installation (12.13.2.1)

CH = adjustment factor for shallow cover heights over metal box culverts (12.9.4.4)

Cll = live load adjustment coefficient for axle loads, tandem axles, and axles with other than four wheels; C1 C2 AL (12.9.4.2)

CN = parameter that is a function of the vertical load and vertical reaction (12.10.4.3.2a)

CS = construction stiffness for tunnel liner plate (N/mm) (12.5.6.4)

C1 = 1.0 for single axles, 0.5 + 8/15 000-1.0 for tandem axles; adjustment coefficient for number of axles; (12.9.4.2) (12.9.4.3)

863


C2 = adjustment factor for number of wheels on a design axle as specified in Table 1; adjustment coefficient for number of wheels per axle (12.9.4.2) (12.9.4.3)

c = distance from inside face to neutral axis of thermoplastic pipe (mm); distance from inside surface to neutral axis (mm) (12.12.3.7) (12.12.3.6)

D = straight leg length of haunch (mm); pipe diameter (mm); required D-load capacity of

Reinforced concrete pipe (N/mm) (12.9.4.1) (12.6.6.2) (12.10.4.3.1)

D-load = resistance of pipe from three-edge bearing test load to produce a 0.25 mm crack (N/mm) (12.10.4.3)

De = effective diameter of thermoplastic pipe (mm) (12.12.3.7)

Di = inside diameter of pipe, mm (12.10.4.3.1)

d = distance from compression face to centroid of tension reinforcement (mm) (12.10.4.2.4a)

E = long-term, i.e., 50-year, modulus of elasticity of the plastic (MPa) (12.12.3.3)

Em = modulus of elasticity of metal (MPa) (12.7.2.4)

Fc = factor for the effect of curvature on diagonal tension, shear, strength in curved components (12.10.4.2.5)

Fcr = factor for adjusting crack control relative to average maximum crack width of 0.25 mm corresponding to F cr = 1.0 (12.10.4.2.4d)

Fd = factor for crack depth effect resulting in increase in diagonal tension, shear, and strength with decreasing d (12.10.4.2.5)

Fe = soil-structure interaction factor for embankment installations (12.10.2.1)

FF = flexibility factor (mm/N) (12.5.6.3) (12.7.2.6)

Fn = coefficient for effect of thrust on shear strength (12.10.4.2.5)

864


Frp = factor for process and local materials affecting radial tension strength of pipe (12.10.4.2.3)

865


Frt = factor for pipe size effect on radial tension strength (12.1 0.4.2.4c)

Ft = soil-structure interaction factor for trench installations (12.10.2.1)

Fu = specified minimum tensile strength (MPa) (12.7.2.4)

Fvp = factor for process and local materials that affect the shear strength of the pipe (12.10.4.2.3)

Fy = yield strength of metal (MPa) (12.7.2.3)

f/c = compressive strength of concrete (MPa) (12.4.2.2)

fcr = critical buckling stress (MPa) (12.7.2.4)

fy = specified minimum yield point for reinforcing steel (MPa) (12.10.4.2.4a)

H = height of cover from the box culvert rise to top of pavement (mm); height of cover over crown (mm); height of fill above top of pipe or box (mm) (12.9.4.2) (12.9.4.4) (12.10.2.1)

HAF= horizontal arching factor (12.10.2.1)

H1 = height of cover above the footing to traffic surface (mm) (12.8.4.2)

H2 = height of cover from the structures springline to traffic surface (mm) (12.8.4.2)

h = wall thickness of pipe (mm); height of ground surface above top of pipe (mm) (12.10.4.2.4a)

hw = height of water surface above top of pipe (mm) (12.12.3.6)

I = moment of inertia (mm4/mm) (12.7.2.6)

ID = inside diameter (mm) (12.6.6.3)

K = ratio of the unit lateral effective soil pressure to unit vertical effective soil pressure, i.e., Rankine coefficient of active earth pressure (12.10.4.2)

k = soil stiffness factor (12.7.2.4) (12.13.3.3)

L = length of stiffening rib on leg (mm) (12.9.4.1)

Lw = lane width (mm) (12.8.4.2)

866


Mdl = dead load moment (N.mm/mm); sum of the nominal crown and haunch dead load moments (N.mm/mm) (12.9.4.2)

MdIu = factored dead load moment as specified in Article 12.9.4.2 (N.mm) (12.9.4.3)

Mll = live load moment (N.mm/mm); sum of the nominal crown and haunch live load moments (Nmm/mm) (12.9.4.2)

Mllu = live load moment as specified in Article 12.9.4.2 (N.mm) (12.9.4.3)

Mnu = factored moment acting on cross-section width “b” as modified for effects of compressive or tensile thrust (N.mm/mm) (12.10.4.2.5)

Mpc = crown plastic moment capacity (N.mm/mm) (12.9.4.3)

Mph = haunch plastic moment capacity (N.mm/mm) (12.9.4.3)

Ms = soil modulus (MPa); bending moment at service limit state (N.mm/mm) (12.12.3.6) (12.l0.4.2.4d)

Mu = ultimate moment acting on cross-section width (N.mm/mm) (l2.l0.4.2.4a)

Ns = axial thrust acting on cross-section of width at service limit state (N/mm) (12.10.4.2.4d)

Nu = axial thrust acting on cross-section width at strength limit state (N/mm) (12.10.4.2.4a)

n = number of adjoining traffic lanes (12.8.4.2)

Pc = proportion of total moment carried by crown of metal box culvert (12.9.4.3)

PL = factored design crown pressure (MPa) (12.7.2.2)

867


P1 = horizontal pressure from the structure at a distance d1 (MPa) (12.8.5.3)

p = positive projection ratio (12.1 0.4.3.2a)

p/ = negative projection ratio (12.1 0.4.3.2a)

q = ratio of the total lateral pressure to the total vertical pressure (12.1 0.4.3.2a)

R = rise of structure (mm); rise of box culvert or long-span structural plate structures (mm); radius of pipe (mm) (12.8.4.1) (12.9.4.1) (12.12.3.6)

RAL = axle load correction factor (12.9.4.6)

Rc = concrete strength correction factor (12.9.4.6)

Rd = ratio of resistance factors specified in Article 5.5.4.2 for shear and moment (12.10.4.2.4c)

Rf = factor related to required relieving slab thickness, applicable for box structures where the span is less than 8000 mm (12.9.4.6)

RH = horizontal reaction component (N/mm) (12.8.4.2)

Rh = haunch moment reduction factor (12.9.4.3)

Rn = nominal resistance (N/mm) (12.5.1)

Rr = factored resistance (N/mm) (12.5.1)

RT = top arc radius of long-span structural plate structures (mm) (12.8.3.2)

Rv = vertical footing reaction component (N/mm) (12.8.4.2)

r = radius of gyration (mm); radius to centerline of concrete pipe wall (mm) (12.7.2.4) (12.10.4.2.5)

rc = radiusofcrown(mm)(l2.9.4.l)

rh = radius of haunch (mm) (12.9.4.1)

rs = radius of the inside reinforcement (mm) (l2.l0.4.2.4c)

rsd = settlement ratio parameter (12.1 0.4.3.2a)

868


S = pipe, tunnel, or box diameter or span (mm); span of structure between springlines of long-span structural plate structures (mm); box culvert span (12.6.6.3) (12.8.4.1) (12.9.4.2)

Si = internal diameter or horizontal span of the pipe (mm) (12.1 0.4.2.4b)

Sl = spacing of circumferential reinforcement (mm) (l2.l0.4.2.4d)

sv = spacing of stirrups (mm) (12.10.4.2.6)

T = total dead load and live load thrust in the structure (N/mm) (12.8.5.3)

TL = factored thrust (N/mm) (12.7.2.2)

t = required thickness of cement concrete relieving slab (mm) (12.9.4.6)

tb = basic thickness of cement concrete relieving slab (mm); clear cover over reinforcement (mm) (12.9.4.6) (12.1 0.4.2.4d)

V = footing reaction in the direction of the box culvert straight side (N/mm) (12.9.4.5)

VAF= vertical arching factor (12.10.2.1)

Vc = factored shear force acting on cross-section width which produces diagonal tension failure without stirrup reinforcement (N/mm) (12.10.4.2.6)

VDL = g [H2(S) AT] Vs(2 x l09) (12.8.4.2)

VLL = nAL (2400+2H1) (l2.8.4.2)

Vn = nominal shear resistance of pipe section without radial stirrups per unit length of pipe (N/mm) (12.10.4.2.5)

Vr = factored shear resistance per unit length (N/mm) (12.10.4.2.5)

Vu = ultimate shear force acting on cross-section width (N/mm) (12.10.4.2.5)

WE = total earth load on pipe or liner (N/mm) (12.10.2.1)

WF = fluid load in the pipe (N/mm) (12.10.4.3.1)

WL = total live load on pipe or liner (N/mm) (12.10.4.3.1)

WT = total dead and live load on pipe or liner (N/mm) (12.10.4.3.1)

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x = parameter which is a function of the area of the vertical projection of the pipe over which active lateral pressure is effective (l2.l0.4.3.2a)

= density of backfill (kg/m3); density of soil (kg/m3) (12.9.2.2) (12.9.4.2)

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= return angle of the structure (DEG); haunch radius included angle (DEG) (12.8.4.2) (12.9.4.1)

= coefficient of friction between the pipe and soil (12.10.2.1.2)


f = resistance factor for flexure (12.1 0.4.2.4c)

fs = coefficient of friction between the fill material and the sides of the trench (l2.l0.4.3.2a)

r = resistance factor for radial tension (12.1 0.4.2.4c)

= central angle of pipe subtended by assumed distribution of external reactive force (DEG) (12.10.4.2.1)

12.4. SOIL AND MATERIAL PROPERTIES

12.4.1.1. Determination of Soil Properties

12.4.1.1. General

Subsurface exploration shall be carried out to determine the presence and influence of geologic and environmental conditions that may affect the performance of buried structures. For buried structures supported on footings and for pipe arches and large diameter pipes, a foundation investigation should be conducted to evaluate the capacity of foundation materials to resist the applied loads and to satisfy the movement requirements of the structure.

12.4.1.2 . Foundation soils

The type and anticipated behavior of the foundation soil shall be considered for stability of bedding and settlement under load.

12.4.1.3. Envelope backfill soils

The type, compacted density and strength properties of the soil envelope adjacent to the buried structure shall be established. The backfill soils comprising ii envelope shall conform to the requirements of AASHTO M 145 as follows:

For standard flexible pipes and concrete structures: A-1, A-2, or A-3 (GW, GP, SW, SP, GM, SM, SC, GC),

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For metal box culverts and long-span structures with cover less than 3600 mm: A-1, A-2-4, A-2-5, or A-3 (GW, GP, SW, SP, GM, SM, SC, GC), and

For long-span metal structures with cover not less than 3600 mm: A-1 or A-3 (GW, GP, SW, SP, GM, SM).

12.4.2. Materials

12.4.2.1. Aluminum pipe and structural plate structures

Aluminum for corrugated metal pipe and with the requirements of AASHTO 196M (ASTM B 745M). Aluminum for plate pipe, pipe - arch, arch and box structures shall meet the requirements of AASHTO M 219M (ASTM B 746M) .

12.4.2.2. Concrete

Concrete shall conform to Article 5.4, except that f/c may be based on cores.

12.4.2.3. Precast concrete pipe

Precast concrete pipe shall comply with the requirements of AASHTO M 170M (ASTM C 76M) and M 242M (ASTM C 655M). Design wall thickness, other than the standard wall dimensions, may be used, provided that the design complies with all applicable requirements of Section 12.

12.4.2.4. Precast concrete structures

Precast concrete arch, elliptical, and box structures shall comply with the requirements of AASHTO M 206M (ASTM C 506M), M 207M (ASTM C 507M), M 259M. (ASTM C 789M), and M 273M (ASTM C 850M).

12.4.2.5. Steel pipe and structural plate structures

Steel for corrugated metal pipe and pipe-arches shall comply with the requirements of AASHTO M 36M (ASTM A 760M). Steel for structural plate pipe, pipe-arch, arch, and box structures shall meet the requirements of AASHTO M 167M (ASTM A 761M).

12.4.2.6. Steel reinforcement

Reinforcement shall comply with the requirements of Article 5.4.3, and shall conform to one of the following AASHTO M 3lM (ASTM A 6l5M), M 32 (ASTM A 82), M 55M (ASTM A 185). M 221M (ASTM A 497), or M 225M (ASTM A 496).

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For smooth wire and smooth welded wire fabric, the yield strength may be taken as 450 MPa. For deformed welded wire fabric, the yield strength may be taken as 480 MPa.

12.4.2.7. Thermoplastic pipe

Plastic pipe may be solid wall, corrugated or profile wall and may be manufactured of polyethylene (PE) or polyvinyl chloride (PVC).

PE pipe shall comply with the requirements of ASTM F 714 for solid wall pipe, AASHTO M 294 for corrugated pipe, and ASTM F 894 for profile wall pipe.

PVC pipe shall comply with the requirements of AASHTO M 278 for solid wall pipe, ASTM F 679 for solid wall pipe, and AASHTO M 304 for profile wall pipe.


12.5.1. General

Buried structures and their foundations shall be designed by the appropriate methods specified in Articles 12.7 through 12.12 so that they resist the factored loads given by the load combinations specified in Articles 12.5.2 and 12.5.3.

The factored resistance, Rr, shall be calculated for each applicable limit state as:

Rr = Rn (12.5.11)

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where:

Rn = the nominal resistance

= the resistance factor specified in Table 12.5.5-1

12.5.2. Service Limit State

Buried structures shall be investigated at Service Load Combination as specified in Table 3.4.1-1.

Deflection of metal structures, tunnel liner plate, and thermoplastic pipe, and

Crack width in reinforced concrete structures.


Buried structures and tunnel liners shall be investigated for construction loads and at Strength Load Combination as specified in Table 3.4.1-1, as follows:

For metal structures:

wall area

buckling

seam failure

flexibility limit for construction

flexure of box structures only

For concrete structures:

flexure

shear

thrust

radial tension

For thermoplastic pipe:

wall area

buckling

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flexibility limit

For tunnel liner plate

wall area

buckling

seam strength

construction stiffness

12.5.4. Load Modifiers and Load Factors

Load modifiers shall be applied to buried structures and tunnel liners as specified in Article 1.3, except that the load modifiers for construction loads should be taken as 1.0. For strength limit states, buried structures shall be considered nonredundant under earth fill and redundant under live load and dynamic load allowance loads. Operational importance shall be determined on the basis of continued function and/or safety of the roadway.

12.5.5. Resistance Factors

Resistance factors for buried structures shall be taken as specified in Table 12.5.5-1. Values of resistance factors for the geotechnical design of foundations for buried structures shall be taken as specified in Section 10.

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Table 12.5.5-1. Resistance Factors for Buried Structures

12.5.6. Flexibility Limits and Construction Stiffness

12.5.6.1. corrugated metal pipe and structural plate structures

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Flexibility factors for corrugated metal pipe and structural plate structures shall not exceed the values specified in Table 1.

Table 12.5.6.1-1- Flexibility Factor Limit

12.5.6.2. Spiral rib metal pipe and pipe arches

Flexibility factors for spiral rib metal pipe and pipe arches shall not exceed the values, specified in Table 1, for embankment installations conforming to the provisions of Articles 12.6.6.2 and 12.6.6.3 and for trench installations conforming to the provisions of Articles 12.6.6.1 and 12.6.6.3.

Table 12.5.6.2-1- Flexibility Factor Limits

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Values of inertia, I, for steel and aluminum pipes and pipe arches shall be taken as tabulated in Tables A12-2 and A12-5.

12.5.6.3. Thermoplastic pipe

Flexibility factor, FF, of thermoplastic pipe shall not exceed 0.54 mm/N.

12.5.6.4. Steel tunnel liner plate

Construction stiffness, Cs, in N/mm, shall not be less than the following:

Two-flange liner plate: Cs 8.75 (N/mm)

Four-flange liner plate: Cs 19.5 (N/mm)

12.6. GENERAL DESIGN FEATURES

12.6.1. Loading

Buried structures shall be designed for force effects resulting from horizontal and vertical earth pressure, pavement load, live load, and vehicular dynamic load allowance. Earth surcharge, live load surcharge, and downdrag loads shall also be evaluated where construction or site conditions warrant. Water buoyancy loads shall be evaluated for buried structures with inverts below the water table to control flotation, as indicated in Article 3.7.2. Earthquake loads should be considered only where buried structures cross active faults.

For vertical earth pressure, the maximum load factor from Table 3.4.1-2 shall apply.

Wheel loads shall be distributed through earth fills according to the provisions of Article 3.6.1.2.6.


12.6.2.1. Tolerable movement

Tolerable movement criteria for buried structures shall be developed based on the function and type of structure, anticipated service life, and consequences of unacceptable movements.

12.6.2.2. Settlement

12.6.2.2.1. General

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Settlement shall be determined as specified in Article 10.6.2. Consideration shall be given to potential movements resulting from:

Longitudinal differential settlement along the length of the pipe,

Differential settlement between the pipe and backfill, and

Settlement of footings and unbalanced loading of skewed structures extending through embankment slopes.

12.6.2.2.2. Longitudinal Differential Settlement

Differential settlement along the length of buried structures shall be determined in accordance with Article 10.6.2.2.3. Pipes and culverts subjected to longitudinal differential settlements shall be fitted with positive joints to resist disjointing forces.

Camber may be specified for an installation to ensure hydraulic flow during the service life of the structure.

12.6.2.2.3. Differential Settlement Between Structure and Backfill

Where differential settlement of arch structures is expected between the structure and the side fill, the foundation should be designed to settle with respect to the backfill.

Pipes with inverts shall not be placed on foundations that will settle much less than the adjacent side fill, and a uniform bedding of loosely compacted granular material should be provided.

12.6.2.2.4. Footing Settlement

Footings shall be designed to provide uniform longitudinal and transverse settlement. The settlement of footings shall be large enough to provide protection against possible downdrag forces caused by settlement of adjacent fill. If poor foundation materials are encountered, consideration shall be given to excavation of all or some of the unacceptable material and its replacement with compacted acceptable material.

Footing design shall comply with the provisions of Article 10.6.

Footing reactions for metal box culvert structures shall be determined as specified in Article 12.9.4.5.

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The effects of footing depth shall be considered in the design of arch footings. Footing reactions shall be taken as acting tangential to the arch at the point of connection to the footing and to be equal to the thrust in the arch at the footing.

12.6.2.2.5. Unbalanced Loading

Buried structures skewed to the roadway alignment and extending through an embankment fill shall be designed in consideration of the influence of unsymmetrical loading on the structure section.

12.6.2.3. Uplift

Uplift shall be considered where structures are installed below the highest anticipated groundwater level.


12.6.3.1. Bearing resistance and stability

Pipe structures and footings for buried structures shall be investigated for bearing capacity failure and erosion of soil backfill by hydraulic gradients.

12.6.3.2. Corner backfill for metal pipe arches

The corner backfill for metal pipe arches shall be designed to account for corner pressure taken as the arch thrust divided by the radius of the pipe-arch corner. The soil envelope around the corners of pipe arches shall resist this pressure. Placement of select structural backfill compacted to densities higher than normal may be specified.

12.6.4. Hydraulic Design

Design criteria, as specified in Article 2.6 and in Chapter 10 of Specification for Road Design, shall apply for hydraulic design.

12.6.5. Scour

Buried structures shall be designed so that no movement of any part of the structure will occur as a result of scour.

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In areas where scour is a concern, the wingwalls shall be extended far enough from the structure to protect the structural portion of the soil envelope surrounding the structure. For structures placed over erodible deposits, a cutoff wall or scour curtain, extending below the maximum anticipated depth of scour or a paved invert, shall be used. The footings of structures shall be placed not less than 600 mm below the maximum anticipated depth of scour.

12.6.6. Soil Envelope

12.6.6.1. Trench installations

The minimum trench width shall provide sufficient space between the pipe and the trench wall to ensure sufficient working room to properly and safely place and compact backfill material.

The contract documents shall require that stability of the trench be ensured by either sloping the trench walls or providing support of steeper trench walls in conformance with Ministry of Labor or other regulatory requirements.

12.6.6.2. Embankment installations

The minimum width of the soil envelope shall be sufficient to ensure lateral restraint for the buried structure. The combined width of the soil envelope and embankment beyond shall be adequate to support all the loads on the culvert and to comply with the movement requirements specified in Article 12.6.2.

12.6.6.3. Minimum soil cover

The cover of a well-compacted granular subbase, taken from the top of rigid pavement or the bottom of flexible pavement, shall not be less than that specified in Table 1, where:

S = diameter of pipe (mm)

Bc = outside diameter or width of the structure (mm)

B’c = out-to-out vertical rise of pipe (mm)

ID = inside diameter (mm)

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Table 12.6.6.3-1 - Minium Soil Cover

If soil cover is not provided, the top of precast or cast-in-place reinforced concrete box structures shall be designed for direct application of vehicular loads.

12.6.7. Minimum Spacing Between Multiple Lines of Pipe

The spacing between multiple lines of pipe shall be sufficient to permit the proper placement and compaction of backfill below the haunch and between the structures.

Contract documents should require that backfihling be coordinated to minimize unbalanced loading between multiple, closely spaced structures. Backfill should be kept level over the series of structures when possible. The effects of significant roadway grades across a series of structures shall be investigated for the stability of flexible structures subjected to unbalanced loading.

12.6.8. End Treatment

12.6.8.1. General

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Protection of end slopes shall be given special consideration where backwater conditions occur or where erosion or uplift could be expected. Traffic safety treatments, such as a structurally adequate grating that conforms to the embankment slope, extension of the culvert length beyond the point of hazard, or provision of guide rail, should be considered.

12.6.8.2. Flexible culverts constructed on skew

The end treatment of flexible culverts skewed to the roadway alignment and extending through embankment fill shall be warped to ensure symmetrical loading along either side of toe pipe or toe headwall shall be designed to support toe full thrust force of the cut end.

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12.6.9. Corrosive and Abrasive Conditions

The degradation of structural resistance due to corrosion and abrasion shall be considered.

If the design of metal or thermoplastic culvert is controlled by flexibility factors during installation, the requirements for corrosion and/or abrasion protection may be reduced or eliminated, provided that it is demonstrated that the degraded culvert will provide adequate resistance to loads throughout the service life of the structure.

12.7. METAL PIPE, PIPE ARCH, AND ARCH STRUCTURES

12.7.1. General

The provisions herein shall apply to the design of buried corrugated and spiral rib metal pipe and structural plate pipe structures.

Corrugated metal pipe and pipe-arches may be of riveted, welded, or lockseam fabrication with annular or helical corrugations. Structural plate pipe, pipe-arches, and arches shall be bolted with annular corrugations only.

The rise-to-span ratio of structural plate arches shall not be less than 0.3.

The provisions of Article 12.8 shall apply to structures with a radius exceeding 4000 mm.


Corrugated and spiral rib metal pipe and pipe arches and structural plate pipe shall be investigated at the strength limit state for:

Wall are a of pipe,

Buckling strength, and

Seam resistance for structures with longitudinal seams.

12.7.2.1. Section properties

Dimensions and properties of pipe cross-sections, minimum seam strength; mechanical and chemical requirements for aluminum corrugated and steel corrugated pipe and pipe-arch sections; and aluminum and steel corrugated structural plate pipe, pipe-arch, and arch sections, may be taken as given in Appendix A12.

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12.7.2.2. Thrust

The factored thrust, TL, per unit length of wall shall be taken as:

TL = PL (12.7.2.2-1)

where:

TL = factored thrust per unit length (N/mm)

S = pipe span(mm)

PL = factored crown pressure (MPa)

12.7.2.3. Wall resistance

The factored axial resistance, Rn, per unit length of wall, without consideration of buckling, shall be taken as:

Rn = Fy A (12.7.2.3-1)

where:

A = wall area (mm2/mm)

Fy = yield strength of metal (MPa)

= resistance factor as specified in Article 12.5.5

12.7.2.4. Resistance to buckling

The wall area, calculated using Equation 12.7.2.3-1, shall be investigated for buckling. If fcr < Fy, A shall be recalculated using fcr in lieu of Fy.

If S < (12.7.2.4-1)

then:

If S > (12.7.2.4-2)

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then:

where

Em = modulus of elasticity of metal (MPa)

Fu = tensile strength of metal (MPa)

r = radius of gyration of corrugation (mm)

k = soil stiffness factor taken as 0.22

S = diameter of pipe or span of plate structure (mm)

12.7.2.5. Seam resistance

For pipe fabricated with longitudinal seams, the nominal resistance of the seam shall be sufficient to develop the factored thrust in the pipe wall, TL.

12.7.2.6. Handling and installation requirements

Handling flexibility shall be indicated by a flexibility factor determined as:

FF = (12.7.2.6-1)

where:

S = diameter of pipe or span of plate structure (mm)

I = moment of inertia of wall (mm4/mm)

Values of the flexibility factors for handling and installation shall not exceed the values for steel and aluminum pipe and plate pipe structures as specified in Article 12.5.6.

12.7.3. Smooth Lined Pipe

Corrugated metal pipe composed of a smooth liner and corrugated shell attached integrally at helical seams, spaced not more than 760 mm apart, may be designed on the same basis as a standard corrugated metal pipe having the same corrugations as the shell and a weight per mm not less than the sum of the weights per mm of liner and helically corrugated shell.

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The pitch of corrugations shall not exceed 75 mm, and the thickness of the shell shall not be less than 60 percent of the total thickness of the equivalent standard pipe.

12.7.4. Stiffening Elements for Structural Plate Structures

The stiffness and flexural resistance of structural plate structures may be increased by adding circumferential stiffening elements to the crown. Stiffening elements shall be symmetrical and shall span from a point below the quarter-point on one side of the structure, across the crown, and to the corresponding point on the opposite side of the structure.

12.7.5. Construction and Installation

The contract documents shall require that construction and installation conform to Section 603 of the Construction Specification.

12.8. LONG-SPAN STRUCTURAL PLATE STRUCTURES

12.8.1. General

The provisions herein and in Article 12.7 shall apply to the structural design of buried long-span structural plate corrugated metal structures.

The following shapes, illustrated in Figure 1, shall be considered long-span structural plate structures:

Structural plate pipe and arch shape structures that require the use of special features specified in Article 12.8.3.5, and

Special shapes of any size having a radius of curvature greater than 4000 mm in the crown or side plates. Metal box culverts are not considered long-span structures and are covered in Article 12.9.

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Figure 12.8.1-1 - Long-Span Shapes


No service limit state criteria need be required.


With the exception of the requirements for buckling and flexibility, the provisions of Article 12.7 shall apply, except as described herein.

Dimensions and properties of structure cross-sections, minimum seam strength, mechanical and chemical requirements, and bolt properties for long-span structural plate sections shall be taken as specified in Appendix A12 or as described herein.


12.8.3.1.1. Cross-Section

The provisions of Article 12.7 shall apply, except as specified.

Structures not described herein shall be regarded as special designs.

Table A12-3 shall apply. Minimum requirements for section properties shall be taken as specified in Table 1. Covers that are less than that shown in Table 1 and

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that correspond to the minimum plate thickness for a given radius may be used if ribs are used to stiffen the plate. If ribs are used, the plate thickness may not be reduced below the minimum shown for that radius, and the moment of inertia of the rib and plate section shall not be less than that of the thicker unstiffened plate corresponding to the fill height. Use of soil cover less than the minimum values shown for a given radius shall require a special design.

Design not covered in Table 1 should not be permitted unless substantiated by documentation acceptable to the Owner.

Table 12.8.3.1.1-1 - Minimum Requirements for Long-Span Acceptable Special Features

12.8.3.1.2. Shape Control

The requirements of Articles 12.7.2.4 and 12.7.2.6 shall not apply for the design of long-span structural plate structures.

12.8.3.3. Mechanical and Chemical Requirements

Tables A12-3, A12-8, and A12-10 shall apply.

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12.8.3.2. Thrust

The factored thrust in the wall shall be determined by Equation 12.7.2.2-1, except the value of S in the equation shall be replaced by twice the value of the top arc radius, RT.

12.8.3.3. Wall area


12.8.3.4. Seam strength

The provisions of Article 12.7.2.5 shall apply

12.8.3.5. Acceptable special features

12.8.3.5.1. Continuous Longitudinal Stiffeners

Continuous longitudinal stiffeners shall be connected to the corrugated plates at each side of the top arc. Stiffeners may be metal or reinforced concrete either singly or in combination.

12.8.3.5.2. Reinforcing Ribs

Reinforcing ribs formed from structural shapes may be used to stiffen plate structures. Where used, they should be:

Curved to conform to the curvature of the plates,

Fastened to the structure as required to ensure integral action with the corrugated plates, and

Spaced at such intervals as necessary to increase the moment of inertia of the section to that required for design.

12.8.4. Safety Against Structural Failure – Foundation Design

12.8.4.1. Settlement limits

A geotechnical survey of the site shall be made to determine that site conditions will satisfy the requirement that both the structure and the critical backfill zone on each side of the structure be properly supported. Design shall satisfy the requirements of Article 12.6.2.2, with the following factors to be considered when establishing settlement criteria:

Once the structure has been backfilled over the crown, settlements of the supporting backfill relative to the structure must be limited to control

890


dragdown forces. If the sidefill will settle more than the structure, a detailed analysis may be required.

Settlements along the longitudinal centerline of arch structures must be limited to maintain slope and preclude footing cracks in arches.

Calculated differential settlements across the structure taken from springline-to-springline, , satisfy:

(12.8.4.1-1)

where:

S = span of structure between springlines of long-span structural plate structures (mm)

R = rise of structure (mm)

More restrictive settlement limits may be required where needed to protect pavements or to limit longitudinal differential deflections.

12.8.4.2. Footing reactions in arch structures

Footing reactions may be taken as:

RV = (VDL + VLL) Cos (12.8.4.2-1)

RH = (VDL + V] LL) Sin (12.8.4.2-2)

891


in which:

n = integer [ 2 H1 / Lw + 2] number of adjoining traffic lanes

where:

Rv = vertical footing reaction component (N/mm)

RH = horizontal reaction component (N/mm)

= return angle of the structure (DEG)

AL = axle load (N) taken as 50 percent of all axle loads that can be placed on the structure at one time, i.e.:

145 000 N for the design truck axle

220 000 N for the design tandem axle pair

AT = area of the top portion of the structure above the springline (mm2)

H1 = height of cover above the footing to traffic surface (mm)

H2 = height of cover from the springline of the structure to traffic surface (mm)

Lw = lane width (mm)

= density of soil (kg/m3)

g = acceleration due to gravity (m/sec2)

S = span (mm)

The distribution of live load through the fill shall be based on any accepted methods of analysis.

12.8.4.3. Footing design

Reinforced concrete footings shall be designed in accordance with Article 10.6 and shall be proportioned to satisfy settlement requirements of Article 12.8.4.1.

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12.8.5. Safety Against Structural Failure - Soil Envelope Design

12.8.5.1. General

Structural backfill material in the envelope around the structure shall satisfy the requirements of Article 12.4.1.3 for long-span structures. The width of the envelope on each side of the structure shall be proportioned to limit shape change during construction activities outside the envelope and to control deflections at the service limit state.

12.8.5.2. Construction requirements

The structural backfill envelope shall either extend to the trench wall and be compacted against it or extend a distance adequate to protect the shape of the structure from construction loads. The remaining trench width may be filled with suitable backfill material compacted to satisfy the requirements of Article 12.8.5.3. In embankment conditions, the minimum structural backfill width shall be taken as 1800 mm. Where dissimilar materials not meeting geotechnical filter criteria are used adjacent to each other, a suitable geotextile shall be provided to avoid migration.

12.8.5.3. Service requirements

The width of the envelope on each side of the structure shall be adequate to limit horizontal compression strain to 1 percent of the structure’s span on each side of the structure.

Determination of the horizontal compressive strain shall be based on an evaluation of the width and quality of the structural backfill material selected as well as the in-situ embankment or other fill materials within the zone on each side of the structure taken to extend to a distance equal to the rise of the structure, plus its cover height as indicated in Figure 1.

Forces acting radially off the small radius corner arc of the structure at a distance d1 from the structure may be taken as:

P1 = (12.8.5.3-1)

where:

P1 = horizontal pressure from the structure at a distance d1 (MPa)

d1 = distance from the structure (mm)

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T = total dead load and live load thrust in the structure (Article 12.8.3.2) (N/mm)

Rc = corner radius of the structure (mm)

The required envelope width adjacent to the pipe, d, may be taken as:

d = (12.8.5.3-2)

where:

d = required envelope width adjacent to the structure (mm)

PBrg = allowable bearing pressure to limit compressive strain in the trench wall or embankment MPa)

The structural backfill envelope shall be taken to continue above the crown to the lesser of:

The minimum cover level specified for that structure,

The bottom of the pavement or granular base course where a base course is present below the pavement, or

The bottom of any relief slab or similar construction where one is present.

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Figure 12.8.5.3-1 - Typical Structural Backfill Envelope and Zone of Structure Influence

12.8.6. Safety Against Structural Failure End Treatment Design

12.8.6.1. General

End treatment selection and design shall be considered as an integral part of the structural design.

12.8.6.2. Standard shell end types

The standard end types for the corrugated plate shell shall be taken to be those shown in Figure 1.

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(C) SKEW CUT END (REQUIRES FULL HEADWALL)

Figure 12.8.6.2-1 - Standard Structure End Types

The following considerations shall apply to step bevels:

The rise of the top step shall be equal to or greater than the rise of the top arc, i.e., plates in the top arc are left uncut.

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For structures with inverts, the bottom step shall satisfy the requirements for a top step.

For arches, the bottom step shall be a minimum of 150 mm high.

The slope of the cut plates generally should be no flatter than 3:1.

The upper edge of the cut plates shall be bolted to and supported by a structural concrete slope collar, slope pavement, or similar device.

Full bevel ends shall be used in special design only. Structures with full inverts shall have a bottom step conforming to the requirements for step bevel ends.

The bevel cut edge of all plates shall be supported by a suitable, rigid concrete slope collar.

Skew cut ends shall be fully connected to and supported by a headwall of reinforced concrete or other rigid construction. The headwall shall extend an adequate distance above the crown of the structure to be capable of reacting the ring compression thrust forces from the cut plates. In addition to normal active earth and live load pressures, the headwall shall be designed to react a component of the radial pressure exerted by the structure as specified in Article 12.8.5.

12.8.6.3. Balanced support

Design and details shall provide soil support that is relatively balanced from side-to-side, perpendicularly across the structure. In lieu of a special design, slopes running perpendicularly across the structure shall not exceed 10 percent for cover heights of 3000 mm or less and 15 percent for higher covers.

When a structure is skewed to an embankment, the fill shall be detailed to be warped to maintain balanced support and to provide an adequate width of backfill and embankment soil to support the ends.

12.8.6.4. Hydraulic protection

12.8.6.4.1. General

In hydraulic applications, provisions shall be made to protect the structure, taken to include the shell, footings, structural backfill envelope, and other fill materials within the zone influenced by the structure.

12.8.6.4.2. Backfill Protection

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Design or selection of backfill gradation shall include consideration of loss of backfill integrity due to piping. If materials prone to piping are used, the structure and ends of the backfill envelope shall be adequately sealed to control soil migration and/or infiltration.

12.8.6.4.3. Cutoff (Toe) Walls

All hydraulic structures with full inverts shall be designed and detailed with upstream and downstream cutoff walls. Invert plates shall be bolted to cutoff walls at a maximum 500 mm center-to-center spacing using 20 mm bolts.

The cutoff wall shall extend to an adequate depth to limit hydraulic percolation to control uplift forces as specified in Article 12.8.6.4.4 and scour as specified in Article 12.8.6.4.5.

898


12.8.6.4.4. Hydraulic Uplift

Hydraulic uplift shall be considered for hydraulic structures with full inverts where the design flow level in the pipe can drop quickly. The design shall provide means to limit the resulting hydraulic gradients, with the water level higher in the backfill than in the pipe, so that the invert will not buckle and the structure will not float. Buckling may be evaluated, as specified in Article 12.7.2.4, with the span of the structure taken as twice the invert radius.

12.8.6.4.5. Scour

Scour design shall satisfy the requirements of 12.6.5. Where erodible soils are encountered, conventional means of scour protection may be employed to satisfy these requirements.

Deep foundations such as piles or caissons should not be used unless a special design is provided to consider differential settlement and the inability of intermittent supports to retain the structural backfill if scour proceeds below the pile cap.

12.8.7. Concrete Relieving Slabs

Concrete relieving slabs may be used to reduce moments in long-span structures.

The length of the concrete relieving slab shall be at least 600 mm greater than the span of the structure. The relieving slab shall extend across the width subject to vehicular loading, and its depth shall be determined as specified in Article 12.9.4.6.


The construction documents shall require that construction and installation conform to Section 603 of the Construction Specification.

12.9. STRUCTURAL PLATE BOX STRUCTURES

12.9.1. General

The design method specified herein shall be limited to depth of cover from 430 to 1500 mm.

The provisions of this article shall apply to the design of structural plate box structures, hereinafter called “metal box culverts.” The provisions of Articles 12.7 and 12.8 shall not apply to metal box culvert designs, except as noted.

899


If rib stiffeners are used to increase the flexural resistance and moment capacity of the plate, the transverse stiffeners shall consist of structural steel or aluminum sections curved to fit the structural plates. Ribs shall be bolted to the plates to develop the plastic flexural resistance of the composite section. Spacing between ribs shall not exceed 600 mm on the crown and 1370 mm on the haunch. Rib splices shall develop the plastic flexural resistance required at the location of the splice.

12.9.2. Loading

For live loads, the provisions of Article 3.6.1 shall apply.

Densities for soil backfill, other than 1900 kg/m3, may be considered as specified in Article 12.9.4.3.

900



No service limit state criteria need be applied in the design of box culvert structures.


12.9.4.1. General

The resistance corrugated box culverts shall be determined at the strength limit state in accordance with Articles 12.5.3, 12.5.4, and 12.5.5 and the requirements specified herein.

Box culvert sections for which these articles apply are defined in Figure 1 and Table 1. Table A12-10 shall apply.

Figure 12.9.4.1-1 - Geometry of Box Culverts

Table 12.9.4.1-1. Geometric requirements for Box culverts

The flexural resistance of corrugated plate box structures shall be determined using the specified yield strength of the corrugated plate.

901


The flexural resistance of plate box structures with ribbed sections shall be determined using specified yield strength values for both rib and corrugated shell. Computed values may be used for design only after confirmation by representative flexural testing. Rib splices shall develop the plastic moment capacity required at the location of the splice.

12.9.4.2 . Moments due to factored loads

Unfactored crown and haunch dead and live load moments, Mdl and Mll, may be taken as:

902


Mdl = { S3 [ 0.0053 - 7.87 x 10-7 (S-3660)] + 0.053

(H-427) S2} (12.9.4.2-1)

Mll = Cll K1 (12.9.4.2-2)

where:

Mdl = sum of the nominal crown and haunch dead load moments (Nmm/mm)

Mll = sum of the nominal crown and haunch live load moments (Nmm/mm)

S = box culvert span(mm)


H = height of cover from the box culvert rise to top of pavement (mm)

Cll = live load adjustment coefficient for axle loads, tandem axles, and axles with other than four wheels

= C1C2AL

AL = sum of all axle loads in an axle group (N)

C1 = 1.0 for single axles, 0.5 + S/15 000 1.0 for tandem axles

C2 = adjustment factor for number of wheels on a design axle as specified in Table 1

in which:

K1 = (12.9.4.2-3)

K1 = (12.9.4.2-

4)

K2 = 5.8 x 10-6 H2 - 0.0013H + 5.05, for 400 H < 900

K2 = 0.0062 H + 3, for 900 H 1500

903


Table 12.9.4.2-1 - Adjustment Coefficient Values (C2) for Number of Wheels per Axle

Unless otherwise specified, the design truck specified in Article 3.6.1.2.2 should be assumed to have four wheels on an axle. The design tandem specified in Article 3.6.1.2.3 should be assumed to be an axle group consisting of two axles with four wheels on each axle.

The factored moments, MdIu and Mllu as referred to in Article 12.9.4.3, shall be determined as specified in Table 3.4.1-1, except that the live load factor used to compute Mllu shall be 2.0. The factored reactions shall be determined by factoring the reactions specified in Article 12.9.4.5.

12.9.4.3. Plastic moment resistance

The plastic moment resistance of the crown, Mpc, and the plastic moment resistance of the haunch Mph, shall not be less than the proportioned sum of adjusted dead and live load moments. The values of Mpc, and Mph shall be determined as follows:

Mpc CH Pc [Mdlu + Mllu] (12.9.4.3-1)

Mph CH [1- Pc] [Mldu + Rh Mllu] (12.9.4.3-2)

where:

CH = crown soil cover factor specified in Article 12.9.4.4

Pc = allowable range of the ratio of total moment carried by the crown as specified in Table 1

RH = acceptable values of the haunch moment reduction factor as specified in Table 2

Mdlu = factored dead load moment as specified in Article 12.9.4.2 (Nmm)

904


Mllu = live load moment as specified in Article 12.9.4.2 (Nmm)

Table 12.9.4.3-1 - Crown Moment Proportioning Values, Pc

Span (mm) Allowable

< 3000 0.55 - 0.70

3000- 4500 0.50 - 0.70

4500-6000 0.45 - 0.70

6000-8000 0.45-0.60

Table 12.9.4.3-2 - Haunch Moment Reduction Values, RH

12.9.4.4. Crown soil cover factor cH

For depths of soil cover less than 1000 mm, the crown soil cover factor, CH, shall be taken as 1.0

For crown cover depth between 420 and 1000 mm, the crown soil cover factor shall be taken as:

CH = 1.15 - (12.9.4.4-1)

where:

H = depth of cover over crown (mm)

12.9.4.5. Footing reactions

Reactions at the box culvert footing shall be determined as:

V = (12.9.4.5-1)

where:

905



V = unfactored footing reaction (N/mm)

s = density of backfill (kg/m3)

H = depth of cover over crown (mm)

R = rise of culvert (mm)

S = span (mm)

AL = total axle load (N)

12.9.4.6. Concrete relieving slabs

Relieving slabs may be used to reduce flexural moments in box culverts. Relieving slabs shall not be in contact with the crown as shown in Figure 1.

The length of the concrete relieving slab shall be at least 600 mm greater than the culvert span and sufficient to project 300 mm beyond the haunch on each side of the culvert. The relieving slab shall extend across the width subject to vehicular loading.

The depth of reinforced concrete relieving slabs shall be determined as:

t = tb RAL + Rc Rf (12.9.4.6-1)

where:

t = minimum depth of slab (mm)

tb = basic slab depth as specified in Table 1 (mm)

RAL = axle load correction factor specified in Table 2

Rc = concrete strength correction factor specified in Table 3

Rf = factor taken as 1.2 for box structures having spans less than 8000 mm

906


Figure 12.9.4.6-1- Metal Box Culverts with Concrete Relieving Slab

Table 12.9.4.6-2. Basic slab depth, tb (Duncan et al. 1985)

Table 12.9.4.6-2. Axle Load Correction Factor, RAL

(Duncan et al. 1985)

Table 12.9.4.6-3. Concrete Strength Correction Factor, Rc

(Duncan et al. 1985)

907


Concrete compesive

Strength, f’c

(MPa)

Rc

21 1.19

24 1.15

28 1.10

31 1.05

34 1.01

38 0.97

41 0.94



12.10. REINFORCED CONCRETE PIPE

12.10.1. General

The provisions herein shall apply to the structural design of buried precast reinforced concrete pipes of circular, elliptical, and arch shapes.

The structural design of the types of pipes indicated above may proceed by either of two methods:

908


The direct design method at the strength limit state as specified in Article 12.10.4.2, or

The indirect design method at the service limit state as specified in Article 12.10.4.3.

12.10.2. Loading

12.10.2.1. Standard installations

The contract documents shall specify that the foundation bedding and backfill comply with the provisions of Article 27.5.2 of the AASHTO LRFD Construction Specification.

Minimum compaction requirements and bedding thickness for standard embankment installations and standard trench installations shall be as specified in Tables 1 and 2, respectively.

Table 12.10.2.1-1. Standard Embankment Installation Soils and Minimum Compaction

Requirements

The following interpretations apply to Table 1:

909


Compaction and soil symbols, i.e., “95 percent SW,” shall be taken to refer to SW soil material with a minimum standard proctor compaction of 95 percent. Equivalent modified proctor values shall be as given in Table 3.

Soil in the outer bedding, haunch, and lower side zones, except within Bc/3 from the pipe springline, shall be compacted to at least the same compaction as the majority of soil in the overfill zone.

The minimum width of a subtrench shall be 1.33 Be, or wider i f required for adequate space to attain the specified compaction in the haunch and bedding zones.

910


For subtrenches with walls of natural soil, any portion of the lower side zone in the subtrench wall shall be at least as firm as an equivalent soil placed to the compaction requirements specified for the lower side zone and as firm as the majority of soil in the overfill zone. Otherwise it shall be removed and replaced with soil compacted to the specified level.

Table 12.10.2.1-2. Standard Trench Installation Soils and Minimum Compaction Requirements

The following interpretations apply to Table 2:

Compaction and soil symbols, i.e., “95% SW,” shall be taken to refer to SW soil material with minimum standard proctor compaction of 95 percent. Equivalent modified proctor values shall be as given in Table 3.

The trench top elevation shall be no lower than 0.1 H below finish grade; for roadways, its top shall be no lower than an elevation of 300 mm below the bottom of the pavement base material.

Soil in bedding and haunch zones shall be compacted to at least the same compaction as specified for the majority of soil in the backfill zone.

911


If required for adequate space to attain the specified compaction in the haunch and bedding zones the trench width shall be wider than that shown in Figures 1 and 2.

For trench walls that are within 10 degrees of vertical, the compaction or firmness of the soil in the trench walls and lower side zone need not be considered.

For trench walls with greater than 10 degree slopes that consist of embankment, the lower side shall be compacted to at least the same compaction as specified for the soil in the backfill zone.

912


The unfactored earth load, WE, shall be determined as:

WE = g Fe Bc H x 10-9 (12.10.2.1-1)where:

WE = earth load (N/mm)

Fe = soil-structure interaction factor for the specified installation as defined herein

Bc = out-to-out horizontal dimension of pipe (mm)

g = acceleration due to gravity (m/s2)

H = height of fill over pile (mm)


The unit weight of soil used to calculate earth load shall be the estimated unit weight for the soils specified for the pipe soil installation but shall not be taken to be less than 1760 kg/m3.

Standard installations for both embankments and trenches shall be designed for positive projection, embankment loading conditions where Fe shall be taken as the vertical arching factor, VAF, specified in Table 1 for each type of standard installation.

For standard installations, the earth pressure distribution shall be the Heger pressure distribution shown in Figure 1 and Table 3 for each type of standard installation.

913


Figure 12.10.2.1-1- Heger Pressure Distribution and Arching Factors

914


Table 12.10.2.1-3- Coefficients for use with Figure 1

Installation Type

1 2 3 4

VAF 1.35 1.40 1.40 1.45

HAF 0.45 0.40 0.37 0.30

A1 0.62 0.85 1.05 1.45

A2 0.73 0.55 0.35 0.00

A3 1.35 1.40 1.40 1.45

A4 0.19 0.15 0.10 0.00

A5 0.08 0.08 0.10 0.11

A6 0.18 0.17 0.17 0.19

a 1.40 1.45 1.45 1.45

b 0.40 0.40 0.36 0.30

c 0.18 0.19 0.20 0.25

e 0.08 0.10 0.12 0.00

f 0.05 0.05 0.05 -

u 0.80 0.82 0.85 0.90

v 0.80 0.70 0.60 -

The following shall apply to Table 3:

VAF and HAF are vertical and horizontal arching factors. These coefficients represent nondimensional total vertical and horizontal earth loads on the pipe, respectively. The actual total vertical and horizontal loads are (VAF) x (PL) and (HAF) x (PL), respectively, where PL is the prism load.

Coefficients Al through A6 represent the integration of nondimensional vertical and horizontal components of soil pressure under the indicated

915


portions of the component pressure diagrams, i.e., the area under the component pressure diagrams.

The pressures are assumed to vary either parabolically or linearly, as shown in Figure 1, with the nondimensional magnitudes at governing points represented by h1, h2, uh1, vh2, a, and b.

Nondimensional horizontal and vertical dimensions of component pressure regions are defined by c, d, e, uc, vd, and f coefficients, where:

d = (0.5-c-e) (12.10.2.1-2)

(12.10.2.1-3)

(12.10.2.1-4)

12.10.2.2. Pipe fluid weight

The unfactored weight of fluid, WF, in the pipe shall be considered in design based on a fluid density of 1000 kg/m3, unless otherwise specified. For standard installations, the fluid weight shall be supported by vertical earth pressure that is assumed to have the same distribution over the lower part of the pipe as given in Figure 12.10.2.1-1 for earth load.

12.10.2.3. Live loads

Live loads shall be as specified in Article 3.6 and shall be distributed through the earth cover as specified in Article 3.6.1.2.6. For standard installations, the live load on the pipe shall be assumed to have a uniform vertical distribution across the top of the pipe and the same distribution across the bottom of the pipe as given in Figure 12.10.2.1-1.


The width of cracks in the wall shall be investigated at the service limit state for moment and thrust. Generally, the crack width should not exceed 0.25 mm.


12.10.4.1. General

916


The resistance of buried reinforced concrete pipe structures against structural failure shall be determined at the strength limit state for:

Flexure,

Thrust,

Shear, and

Radial tension.

The dimensions of pipe sections shall be determined using either the analytically-based direct design method or the empirically based indirect design method.

When quadrant mats, stirrups and/or elliptical cages are specified in the contract documents, the orientation of the pipe installation shall be specified, and the design shall account for the possibility of an angular misorientation of 100

during the pipe installation.

12.10.4.2. Direct design method

12.10.4.2.1. Loads and Pressure Distribution

The total vertical load acting on the pipe shall be determined as specified in Article 12.10.2.1.

The pressure distribution on the pipe from applied loads and bedding reaction shall be determined from either a soil-structure analysis or from a rational approximation, either of which shall permit the development of a pressure diagram, shown schematically in Figure 1, and the analysis of the pipe.

917


Figure 12.10.4.2.1-1- Suggested Design Presure Distribution Around a Buried Concrete Pipe

for Analysis by Direct Design

12.10.4.2.2. Analysis for Force Effects with the Pipe Ring

918


Force effects in the pipe shall be determined by an elastic analysis of the pipe ring under the assumed pressure distribution or a soil-structure analysis.

12.10.4.2.3. Process and Material Factors

Process and material factors, Frp for radial tension and Fvp for shear strength, for design of plant-made reinforced concrete pipe should be taken as 1.0. Higher values of these factors may be used if substantiated by sufficient testing in accordance with AASHTO M 242M (ASTM C 655M).

12.10.4.2.4. Flexural Resistance at the Strength Limit State

12.10.4.2.4a. Circumferential Reinforcement

Reinforcement for flexural resistance per mm of length shall satisfy:

As (12.1 0.4.2.4a-

1)

for which:

g = 0.85 f’c (12.10.4.2.4a-2)

where:

As = area of reinforcement per mm of pipe (mm2/mm)

fy = specified yield strength of reinforcing (MPa)

d = distance from compression face to centroid of tension reinforcement (mm)

h = wall thickness of pipe (mm)

Mu = moment due to factored loads (Nmm/mm)

Nu = thrust due to factored load, taken to be positive for compression (N/mm)

= resistance factor for flexure specified in Article 12.5.5

12.10.4.2.4b. Minimum Reinforcement

The reinforcement, As, per mm of pipe shall not be less than:

For inside face of pipe with two layrs of reinforcement:

919


As (12.1 0.4.2.4b-1)

For outside face of pipe with two layers of reinforcement:

Aa (12.1 0.4.2.4b-2)

For elliptical reinforcement in circular pipe and for 840 mm diameter and smaller pipe with a single cage of reinforcement in the middle third of the pipe wall:

Ss (12.10.4.2.4b-3)

920


Si = internal diameter or horizontal span of the pipe (mm)

h = wall thickness of pipe (mm)

fy = yield strength of reinforcement (MPa)

12.10.4.2.4c. Maximum Flexural Reinforcement Without Stirrups

The flexural reinforcement per mm of pipe without stirrups shall satisfy:

For inside steel in radial tension:

Asmax (12.1 0.4.2.4c-1)

where:

rs = radius of the inside reinforcement (mm)

f’c = compressive strength of concrete (MPa)

fy = specified yield strength of reinforcement (MPa)

R = ( r/ f); ratio of resistance factors for radial tension and moment specified in Article 12.5.5

Frp = 1.0 unless a higher value substantiated by test data and approved by the Engineer

in which:

For 300 mm S1 1830 mm

Frt = 1 + 0.000328 (1830-Si)

For 1830 mm <Si 3660 mm

Frt =

For Si > 3660 mm

Frt = 0.80

For reinforcing steel in compression:

921


Asmax (12.1 0.4.2.4c-2)

for which:

g’ = f’c [0.85 - 0.0073 (f’

c-28)] (12.1 0.4.2.4c-3)

0.85 f’c g’ 0.65 f/

c (12.1 0.4.2.4c-4)

where:

= resistance factor for flexure Article 5.5.4.2

922


10.4.2.4d. Reinforcement for Crack Width Control

The crack width factor, Fcr, may be determined as:

If Ns is compressive, it is taken as positive and:

Fcr = (12.1 0.4.2.4d-1)

If Ns is tensile, it is taken as negative and:

Fcr = (12.1 0.4.2.4d-

2)

for which:

j = 0.74 + 0.1 (12.10.4.2.4d-3)

i = (12.1 0.4.2.4d-4)

e = (12.10.4.2.4d-5)

B1 = (12.1 0.4.2.4d-6)

where:

Ms = flexural moment at service limit state (N.mm/mm)

Ns = axial thrust at service limit state (N/mm)


h = wall thickness (mm)

f’c = specified compressive strength of concrete (MPa)

C1 = crack control coefficient for various types of reinforcement as specified in Table 1

923


As = area of steel in mm2/mm

tb = clear cover over reinforcement (mm)

Sl = spacing of circumferential reinforcement (mm)

n = 1.0 when tension reinforcement is a single layer

n = 2.0 when tension reinforcement is made of multiple layers

= resistance factor for flexure as specified in Article 12.5.5

Table 12.1 0.4.2.4d-1 - Crack Control Coefficients

For Type 2 reinforcement in Table I having t2b S/n > 50 000, the crack width factor, Fcr, shall also be investigated using coefficients B1 and C1 specified for Type 3 reinforcement, and the larger value for Fcr, shall be used.

Higher values for C1 may be used if substantiated by test data and approved by the Engineer.

12.10.4.2.4e. Minimum Concrete Cover

The provisions of Article 5.12.3 shall apply to minimum concrete cover, except as follows:

If the wall thickness is less than 63 mm, the cover shall not be less than 20 mm, and

If the wall thickness is not less than 63 mm, the cover shall not be less than 26 mm.

12.10.4.2.5. Shear Resistance Without Stirrups

924


The section shall be investigated for shear at a critical section taken where Mu/(Vu d) = 3.0. The factored shear resistance without radial stirrups, V r, shall be taken as:

Vr = Vn (12.10.4.2.5-1)

for which:

Vn = 5.23d Fvp

(12.10.4.2.5-2)

(12.10.4.2.5-3)

For pipes with two cages or a single elliptical cage:

Fd = 0.8 + (12.10.4.2.5-4)

For pipes not exceeding 915 mm diameter with a single circular cage:

Fd = 0.8 + (12.10.4.2.5-5)

925


If Nu is compressive, it is taken as positive and:

Fn = 1 + (12.10.4.2.5-6)

If Nu is tensile, it is taken as negative and:

Fn = 1 + (12.10.4.2.5-7)

Fc = 1 (12.10.4.2.5-8)

Mnu = Mu - Nu (12.10.4.2.5-9)

The algebraic sign in Equation 8 shall be taken as positive where tension is on the inside of the pipe and negative where tension is on the outside of the pipe.

where:

f/cmax = 48MPa


= resistance factor for shear as specified in Article 5.5.4.2

r = radius to centerline of concrete pipe wall (mm)

Nu = thrust due to factored loads (N/mm)

Vu = shear due to factored loads (N/mm)

Fvp = process and material factor specified in Article 12.10.4.2.3

If the factored shear resistance, as determined herein, is not adequate, radial stirrups shall be provided in accordance with Article 12.10.4.2.6.

12.10.4.2.6. Shear Resistance with Radial Stirrups

Radial tension and shear stirrup reinforcement shall not be less than:

For radial tension:

Avr = (12.10.4.2.6-1)

926


Sv (12.10.4.2.6-2)

For shear:

Asv = (12.10.4.2.6-3)

Sv (12.10.4.2.6-4)

for which:

Vc = (12.10.4.2.6-5)

where:

Mu = flexural moment due to factored loads (N.mm/mm)

Mnu = factored moment acting on cross-section width “b” as modified for effects of compressive or tensile thrust (Nmm/mm)

Nu = thrust due to factored loads (N/mm)

Vu = shear due to factored loads (N/mm)

Vc = shear resistance of concrete section (N/mm)


fy = specified yield strength for reinforcement; the value of fy shall be taken as the lesser of the yield strength of the stirrup or its developed anchorage capacity (MPa)

rs = radius of inside reinforcement (mm)

sv = spacing of stirrups (mm)

Vr = factored shear resistance of pipe section without radial stirrups per unit length of pipe (N/mm)

Avr = stirrup reinforcement area to resist radial tension forces on cross-section of unit width in each line of stirrups at circumferential spacing “sv” (mm2/mm)

Avs = required area of stirrups reinforcement (mm2/mm)

927


F’c = compressive strength of concrete (MPa)

= resistance factor for shear as specified in Article 12.5.5

= resistance factor for radial tension as specified in Article 12.5.5

Fc = curvature factor as determined by Equation 12.10.4.2.5-6

12.10.4.2.7. Stirrup Reinforcement Anchorage

12.10.4.2.7a. Radial Tension Stirrup Anchorage

When stirrups are used to resist radial tension, they shall be anchored around each circumferential of the inside cage to develop the resistance of the stirrup, and they shall also be anchored around the outside cage or embedded sufficiently in the compression side to develop the required resistance of the stirrup.

12.10.4.2.7b. Shear Stirrup Anchorage

Except as specified herein, when stirrups are not required for radial tension but required for shear, their longitudinal spacing shall be such that they are anchored around each tension circumferential or every other tension circumferential. The spacing of such stirrups shall not exceed 150 mm.

12.10.4.2. 7c Stirrup Embedment

Stirrups intended to resist forces in the invert and crown regions shall be anchored sufficiently in the opposite side of the pipe wall to develop the required resistance of the stirrup.

12.10.4.3. Indirect design method

12.10.4.3.1. Bearing Resistance

Earth and live loads on the pipe shall be determined in accordance with Article 12.10.2 and compared to three-edge bearing strength D-load for the pipe. The service limit state shall apply using the criterion of acceptable crack width specified herein.

The D-load for a particular class and size of pipe shall be determined in accordance with AASHTO M 242M (ASTM C 655M).

The three-edge bearing resistance of the reinforced concrete pipe, corresponding to an experimentally observed 0.3 mm width crack, shall not be less than the design load determined for the pipe as installed, taken as:

928


D = (12.10.4.3.1-1)

where:

BFE = earth load bedding factor specified in Article 12.1 0.4.3.2a or Article 12.1 0.4.3.2b

BFLL = live load bedding factor specified in Article 12.1 0.4.3.2c

Si = internal diameter of pipe (mm)

WE = total unfactored earth load specified in Article 12.10.2.1 (N/mm)

WF = total unfactored fluid load in the pipe as specified in Article 12.10.2.3 (N/mm)

WL = total unfactored live load on unit length pipe specified in Article 12.10.2.4 (N/mm)

For Type 1 installations, D loads, as calculated above, shall be modified by multiplying by an installation factor of 1.10.

12.10.4.3.2. Bedding Factor

The minimum compaction specified in Tables 12.10.2.1-1 and 12.10.2.1-2 shall be required by the contract document.

12. 10.4.3.2a. Earth Load Bedding Factor for Circular Pipe

Earth load bedding factors, BFE, for circular pipe are presented in Table 1.

For pipe diameters, other than those listed in Table 1, embankment condition bedding factors, BFE, may be determined by interpolation.

929

Specification for Bridge Design930


Table 12.10.4.3.2a-1. Bedding Factors for Circular Pipe

12. 10.4.3.2b. Earth Load Bedding Factor for Arch and Elliptical Pipe

The bedding factor for installation of arch and elliptical pipe shall be taken as:

BFE = (12.10.4.3.2b-1)

where:

CA = constant corresponding to the shape of the pipe, as specified in Table 1

CN = parameter that is a function of the distribution of the vertical load and vertical reaction, as specified in Table 1

x = parameter that is a function of the area of the vertical projection of the pipe over which lateral pressure is effective, as specified in Table I

q = ratio of the total lateral pressure to the total vertical fill load specified herein Design values for CA and x are listed in Table 1.

Table 12.10.4.3.2b-1- Design Values of Parameters in Bedding Factor Equation

931


The value of the parameter q is taken as:

For arch and horizontal elliptical pipe:

q = 0.23 (12.1 0.4.3.2b-2)

For vertical elliptical pipe:

q = 0.48 (12.1 0.4.3.2b-3)

where:

p = projection ratio, ratio of the vertical distance between the outside top of the pipe, and the ground of bedding surface to the outside vertical height of the pipe

12. 10.4.3.2c. Live Load Bedding Factors

The bedding factors for live load, WL, for both circular pipe and arch and for elliptical pipe are given in Table 1. If BFE is less than BFLL, use BFE instead of BFLL, for the live load bedding factor. For pipe diameters not listed in Table 1, the bedding factor may be determined by interpolation.

Table 12.10.4.3.2c-1. Bedding Factors, BFLL, for the Design Truck

932


12.10.4.4. Development of quadrant mat reinforcement

12.10.4.4.1. Minimum Cage Reinforcement

In lieu of a detailed analysis, when quadrant mat reinforcement is used, the area of the main cage shall be no less than 25 percent of the area required at the point of maximum moment.

12.10.4.4.2. Development Length of Welded Wire Fabric

Unless modified herein, the provisions of Article 5.11.2.5 shall apply.

12.10.4.4.3. Development of Quadrant Mat Reinforcement Consisting of Welded Plain Wire Fabric

The embedment of the outermost longitudinals on each end of the circumferentials shall not be less than:

The greater of 12 circumferential bar diameters or three-quarters of the wall thickness of the pipe beyond the point where the quadrant reinforcement is no longer required by the orientation angle, and

A distance beyond the point of maximum flexural stress by the orientation angle plus the development length, Ld , where, Ld , is specified in Article 5.11.2.5.2.

933


The mat shall contain no less than two longitudinals at a distance 25 mm greater than that determined by the orientation angle from either side of the point requiring the maximum flexural reinforcement.

The point of embedment of the outermost longitudinals of the mat shall be at least a distance determined by the orientation angle past the point where the continuing reinforcement is no less than double the area required for flexure.

12.10.4.4.4. Development of Quadrant Mat Reinforcement Consisting of Deformed Bars, Deformed Wire, or Deformed Wire Fabric

When deformed bars, deformed wire, or deformed wire fabric is used, the circumferential bars in quadrant mat reinforcement shall satisfy the following requirements:

Circumferentials shall extend past the point where they are no longer required by the orientation angle plus the greater of 12 wire or bar diameters or three-quarters of the wall thickness of the pipe,

Circumferentials shall extend on either side of the point of maximum flexural stress not less than the orientation angle plus the development length, Ihd ,as required by Article 5.11.2.5.1 and modified by the applicable modification factor or factors, and

Circumferentials shall extend at least a distance determined by the orientation angle past the point where the continuing reinforcement is no less than double the area required for flexure.


The contract documents shall require that the construction and installation conform to Section 603 of the Construction Specification.

12.11. REINFORCED CONCRETE CAST-IN-PLACE AND PRECAST BOX CULVERTS AND REINFORCED CAST-IN-PLACE ARCHES

12.11.1. General

The provisions herein shall apply to the structural design of cast-in-place and precast reinforced concrete box culverts and cast-in-place reinforced concrete arches with the arch barrel monolithic with each footing.

Designs shall conform to applicable articles of these Specifications, except as provided otherwise herein.

934


12.11.2. Loads and Live Load Distribution

12.11.2.1. General

Loads and load combinations specified in Table 3.4.1-1 shall apply. Live load shall be considered as specified in Article 3.6.1.3. Distribution of wheel loads and concentrated loads for culverts with less than 600 mm of cover shall be taken as specified for slab-type superstructures in Article 5.14.4. Requirements for bottom distribution reinforcement in top slabs of such culverts shall be as specified in Article 9.7.3.2.

Distribution of wheel loads to culverts with 600 mm or more of cover shall be as specified in Article 3.6.1.2.6.

The dynamic load allowance for buried structures shall conform to Article 3.6.2.2.

12.11.2.2. Modification of earth loads for soil-structure interaction

12.11.2.2.1. Embankment and Trench Conditions

In lieu of a more refined analysis, the total unfactored earth load, WE, acting on the culvert may be taken as:

For embankment installations:

WE = g Fe Bc H x 10-9 (12.11.2.2.1-1)

in which:

Fe = 1+0.20 (12.11.2.2.1-2)

For trench installations:

WE = g Ft Bc H x 10-9 (12.11.2.2.1-3)

in which:

Ft = (12.11.2.2.1-4)

where:

935



WE = total unfactored earth load (N/mm)

Bc = outside width of culvert as specified in Figures 1 or 2, as appropriate (mm)

H = depth of backfill as specified in Figures 1 and 2 (mm)

Fe = soil-structure interaction factor for embankment installation specified herein

Ft = soil-structure interaction factor for trench installations specified herein

= density of backfill (kg/m3)

Bd = horizontal width of trench as specified in Figure 2 (mm)

Cd = a coefficient specified in Figure 3

Fe shall not exceed 1.15 for installations with compacted fill along the sides of the box section, or 1.40 for installations with uncompacted fill along the sides of the box section.

For wide trench installations where the trench width exceeds the horizontal dimension of the culvert across the trench by more than 300 mm, Ft shall not exceed the value specified for an embankment installation.

Figure 12.11.2.2.1-1- Embankment Condition – Precast Concrete Box Sections

936


Figure 12.11.2.2.1-2- Trench Condition - Precast Concrete Concrete Box Sections

Figure 12.11.2.2.1-3- Coefficient Cd for Trench Installations

937


12.11.2.2. Other Installations

Methods of installation other than embankment or trench may be used to reduce the loads on the culvert, including partial positive projection, 0.0 projection, negative projection, induced trench, and jacked installations. The loads for such installations may be determined by accepted methods based on tests, soil-structure interaction analyses, or previous experience.

12.11.2.3. Distribution of concentrated loads to bottom slab of box culvert

The width of the top slab strip used for distribution of concentrated wheel loads, specified in Article 12.11.2, shall also be used for the determination of moments, shears, and thrusts in the side walls and the bottom slab.

12.11.2.4. Distribution of concentrated loads in skewed box culverts

Wheel distribution specified in Article 12.11.2.3 need not be corrected for skew effects.


The provisions of Article 5.7.3.4 shall apply to crack width control in reinforced concrete cast-in-place and precast box culverts and reinforced cast-in-place arches.

938



12.11.4.1. General

All sections shall be designed for the applicable factored loads specified in Table 3.4.1-1 at the strength limit state, except as modified herein. Shear in culverts shall be investigated in conformance with Article 5.14.5.3.

12.11.4.2. Design moment for box culverts

Where monolithic haunches inclined at 450 are specified, negative reinforcement in walls and slabs may be proportioned based on the flexural moment at the intersection of the haunch and uniform depth member. Otherwise, the provisions of Section 5 shall apply.

12.11.4.3. Minimum reinforcement

12.11.4.3.1. Cast-in-place Structures

Reinforcement shall not be less than that specified in Article 5.7.3.3.2 at all cross-sections subject to fiexural tension, including the inside face of walls. Shrinkage and temperature reinforcement shall be provided near the inside surfaces of walls and slabs in accordance with Article 5.10.8.

12.11.4.3.2. Precast Box Structures

At all cross-sections subjected to flexural tension, the ratio of primary flexural reinforcement in the direction of the span to gross concrete area shall be not less than 0.002. Such minimum reinforcement shall be provided at the inside faces of walls and in each direction at the top of slabs of box sections having less than 600 mm of cover.

The provisions of Article 5.10.8 shall not apply to precast concrete box sections fabricated in lengths not exceeding 5000 mm. Where the fabricated length exceeds 5000 mm, the minimum longitudinal reinforcement for shrinkage and temperature should be in conformance with Article 5.10.8.

12.11.4.4. Minimum cover for precast box structures

The provisions of Article 5.12.3 shall apply unless modified herein for precast box structures.

If the height of the fill is 600 mm, the minimum cover in the top slab shall be 50 mm for all types of reinforcement.

939


Where welded wire fabric is used, the minimum cover shall be the greater of three times the diameter of the wire or 25 mm.



12.12. THERMOPLASTIC PIPES

12.12.1. General

The provisions herein shall apply to the structural design of buried thermoplastic pipe with solid, corrugated, or profile wall, manufactured of PE or PVC.

940


12.12.2. Service Limit States

The allowable maximum localized distortion of installed plastic pipe shall be limited based on the service requirements and overall stability of the installation. The extreme fiber tensile strain shall not exceed the allowable long-term strain in Table 12.12.3.3-1. The net tension strain shall be the numerical difference between the bending tensile strain and ring compression strain.


12.12.3.1. General

Buried plastic pipe structures shall be investigated at the strength limit state for thrust and buckling.


Section properties for PE Corrugated Pipes, PE Ribbed Pipes and PVC Ribbed Pipes may be taken as listed in Appendix A12, Tables A12-1 I through Al 2-1 3, as appropriate.

12.12.3.3. Chemical and mechanical requirements

Mechanical properties for design shall be as specified in Table 1.

Except for buckling, the choice of either initial or 50 year mechanical property requirements, as appropriate for a specific application, shall be determined by the Engineer. Investigation of buckling shall be based on the 50-year value for modulus of elasticity.

Table 12.12.3.3-1- Mechanical Properties of Thermoplastic Pipes

941


12.12.3.4. Thrust

The factored thrust per unit length of wall of buried plastic pipe structures shall be taken as:

TL = PL (12.12.3.4-1)

where:

TL = factored thrust per unit length (N/mm)


PL = factored vertical crown pressure (MPa)

12.12.3.5. Wall resistance

The factored resistance of the wall to thrust, Rr, shall be taken as:

Rr = A Fu (12.12.3.5-1)

where:

942


Fu = tensile strength as specified in Table 12.12.3.3-1 (MPa)

= resistance factor specified in Article 12.5.5

A = wall area (mm2/mm)

12.12.3.6. Buckling

The pipe wall shall be investigated for buckling. If fcr <Fu, the value of A shall be recalculated using fcr in lieu of Fu.

fcr = 0.77 (12.12.3.6-1)

for which:

B = 1-0.33 (12.12.3.6-2)

R = c + (12.12.3.6-3)

where:

fcr = buckling strength of pipe wall (MPa)

c = distance from inside surface to neutral axis (mm)

Ms = soil modulus (MPa)

E = long-term modulus of elasticity as specified in Table 12.12.3.3-1 (MPa)

I = moment of inertia (mm4/mm)

ID = inside diameter (mm)

hw = height of water surface above pipe (mm)

h = height of ground surface above pipe (mm)

For side fills conforming to Article 12.6.6.3, a value of 11.7 MPa may be used for M5 in Equation 1.

12.12.3.7. Handling and installation requirements

The flexibility factor, FF, in mm/N shall be taken as:

943


FF = (12.12.3.7-1)

where:


E = initial modulus of elasticity (MPa)


The flexibility factor, FF, shall be limited as specified in Article 12.5.6.3.

12.12.3.8. Resistance to local buckling of pipe wall

The buckling resistance of corrugated and profile wall pipes shall be verified by testing.

12.13. STEEL TUNNEL LINER PLATE

12.13.1. General

The provisions of this article shall apply to the structural design of steel tunnel liner plates. Construction shall conform to Section 825 of the Construction Specification.

The tunnel liner plate be two-flange, fully corrugated with lapped longitudinal seams or four-flange, partially corrugated with flanged longitudinal seams. Both types shall be bolted together to form annular rings.

12.13.2. Loading

The provisions for earth loads given in Article 3.11.5 shall not apply to tunnels.

12.13.2.1. Earth loads

The provisions of Article 12.4.1 shall apply. When more refined methods of soil analysis are not employed, the earth pressure may be taken as:

WE = g Cdt S x 10-9 (12.13.2.1-1)

where:


Cdt = load coefficient for tunnel installation specified in Figure 1

= total density of soil (kg/rn3)

944


WE = earth pressure at the crown (MPa)

S = tunnel diameter or span (mm)

Figure 12.13.2.1-1. Diagram for Coefficient Cdt for Tunnel in Soil

for which:

H = height of soil over top of tunnel (mm)

12.13.2.2. Live loads


12.13.2.3. Grouting pressure

If the grouting pressure is greater than the computed design load, the design load, WT, on the tunnel liner shall be the grouting pressure.



945


Steel tunnel liner plate shall meet the minimum requirements of Table 1 for cross-sectional properties, Table 2 for seam strength, and Table 3 for mechanical properties.

12.13.3.2. Wall area

The requirements of Articles 12.7.2.2 and 12.7.2.3 shall apply using effective area from Table 12.13.4.1-1.

12.13.3.3. Buckling

The requirements of Articles 12.3.2.2 and 12.7.2.4 shall apply, except that the soil stiffness factor, k, may vary from 0.22 to 0.44 depending upon the quality and extent of the backpacking material used.

12.13.3.4. Seam strength

The requirements of Article 12.7.2.5 shall apply.

12.13.3.5. Construction stiffness

Construction stiffness shall be indicated by a construction stiffness factor as:

Cs = (12.13.3.5-1)

where:

S = diameter or span (mm)

E = modulus of elasticity (MPa)


The value of Cs from Equation 1 shall not be less than the values for steel tunnel liner plate as given in Article 12.5.6.4.

946


Table 12.13.3.1-1 - Cross-Sectional Properties - Steel Tunnel Liner Plate

Table 12.13.3.1-2 - Minimum Longitudinal Seam Strength with Bolt and Nut Requirements for Steel Tunnel Plate

Liner

Plate thickness

2-Flange plate 4-Flange plate

Longitudunal sean bolts

Ultimate

sean strength

(N/mm)

Longitudunal sean bolts

Ultimate sean strengt

h (N/mm)

(mm) Dlameter

Material

ASTM

Dlameter

Material

ASTM

1.91 16 A 307 292 - - -

2.67 16 A 307 438 13 A 307 380

947


3.43 16 A 307 686 13 A 307 628

4.17 16 A 307 803 13 A 307 730

4.55 16 A 307 905 16 A 307 788

5.31 16 A 449 1270 16 A 307 978

6.07 16 A 449 1343 16 A 307 1183

7.95 16 - - 16 A 307 1679

9.53 16 - - 16 A 307 1737

All nuts shall conform to A 307, Grade A or better.

Circumferential seam bolts shall conform to ASTM A 307 or better for all plate thicknesses.

948


Table 12.13.3.1-3 - Mechanical Properties - Steel Tunnel Liner Plate (Plate before Cold

Forming)

12.14. PRECAST REINFORCED CONCRETE THREE-SIDED STRUCTURES

12.14.1. General

The provisions herein shall apply to the design of precast reinforced concrete three-sided structures supported on a concrete footing foundation.

12.14.2. Materials

12.14.2.1. Concrete

Concrete shall conform to Article 5.4.2, except that evaluation of f/c may also be

based on cores.

12.14.2.2. Reinforcement

Reinforcement shall meet the requirements of Article 5.4.3, except that for welded wire fabric a yield strength of 450 MPa may be used. For wire fabric, the spacing of longitudinal wires shall be a maximum of 200 mm. Circumferential welded wire fabric spacing shall not be greater than 100 mm or less than 50 mm. Prestressing, if used, shall be in accordance with Section 5.9.

12.14.3. Concrete Cover for Reinforcement

The minimum concrete cover for reinforcement in precast three-sided structures reinforced with welded wire fabric shall be taken as three times the wire diameter, but not less that 25 mm, except for the reinforcement in the top of the top slab of structures covered by less than 600 mm of fill, in which case the minimum cover shall be taken as 50 mm.

12.14.4. Geometric Properties

949


Except as noted herein, the shape of the precast three-sided structures may vary in span, rise, wall thickness, haunch dimensions, and curvature. Specific geometric properties shall be specified by the manufacturer. Wall thicknesses shall be a minimum of 200 mm for spans under 7300 mm and 250 mm for 7300 mm and larger spans.

12.14.5. Design

12.14.5.1. General

Designs shall conform to applicable sections of these specifications, except as provided otherwise herein. Analysis shall be based on a pinned connection at the footing and shall take into account anticipated footing movement.

950


12.14.5.2. Distribution of concentrated load effects in sides

The width of the top slab strip used for distribution of concentrated wheel loads shall also be used for determination of bending moments, shears, and thrusts in the sides. The strip width shall not exceed the length of a precast unit.

12.14.5.3. Distribution of concentrated loads in skewed culverts

Wheel loads on skewed culverts shall be distributed using the same provisions as given for culverts with main reinforcement parallel to traffic. For culvert elements with skews greater than 150, the effect of the skew shall be considered in analysis.

12.14.5.4. Shear transfer in transverse joints between culvert sections

Shear keys shall be provided in the top surface of the structures between precast units having flat tops under shallow cover.

12.14.5.5. Span length

When monolithic haunches inclined at 450 are taken into account, negative reinforcement in walls and slabs may be proportioned on the basis of bending moment at the intersection of the haunch and uniform depth member.

12.14.5.6. Resistance factors

The provisions of Articles 5.5.4.2 and 1.2.5.5 shall apply as appropriate.

12.14.5.7. Crack control

The provisions of Article 5.7.3.4 for buried structures shall apply.

12.14.5.8. Minimum reinforcement

The provisions of Article 5.10.8.2 shall not be taken to apply to precast three-sided structures.

The primary flexural reinforcement in the direction of the span shall provide a ratio of reinforcement area to gross concrete area at least equal to 0.002. Such minimum reinforcement shall be provided at all cross-sections subject to flexural tension, at the inside face of walls, and in each direction at the top of slabs of threesided sections with less than 600 mm of fill.

951


12.14.5.9. Deflection control at the service limit state

The deflection limits for concrete structures specified in Article 2.5.2.6.2 shall be taken as mandatory and pedestrian usage as limited to urban areas.

12.14.5.10. Footing design

Design shall include consideration of differential horizontal and vertical movements and footing rotations. Footing design shall conform to the applicable articles in Sections 5 and 10.

952


12.14.5.11. Structural backfill

Specification of backfill requirements shall be consistent with the design assumptions used. The contract documents should require that a minimum backfill compaction of 90 percent Standard Proctor Density be achieved to prevent roadway settlement adjacent to the structure. A higher backfill compaction density may be required on structures utilizing a soilstructure interaction system.

12.14.5.12. Scour protection and waterway considerations

The provisions of Article 2.6 shall apply as appropriate.

Table A 12-1. Corrugated Steel Pipe - Cross-Section Properties

Table A 12-1 (Continued)

953


Table A 12-2- Spiral Rib Steel Pipe - Cross-Section Properties

Table A 12-2- Spiral rib steel pipe - Cross-section properties

20 x 26 x 292 corrugation

Thickness

(mm)

A (mm2/mm

r (mm)

1 (mm4/mm)

1.63 0.79 9.73 75.1

954


2.01 1.11 9.47 99.6

2.77 1.87 9.02 152

Note: Effective section properties are taken at full yield stress.

955


Table A 12-3- Steel Structural Plate Cross-Section Properties

Table A12-4- Corrugated Aluminum Pipe- Cross-Section Properties

956



Table A12-4 (continued)

Table A12-5- Aluminum Spiral Rib Pipe-Cross-Section Properties

958



Table A 12-5 (Continues)

Note: Effective section properties are taken at full yield stress.

Table A12-6. Corrugated Aluminum Structure Plate or Pipe Arch – Cross-Section properties

Table A12-7. Minimum Longitudinal Seam Strength Corrugated Aluminum and Steel Pipe

Riveted or Spot Welded

960


Table A 12-7 ( Continued)

961



Table A12-7 (Continued)

Table A12-8- Minimum Longitudinal Seam Strength Steel and Aluminum Structural

Plate - Bolted

963


A12-8 (Continued)

Table A12-9. Mechanical Properties and Spiral Rib for Corrugated Metal Pipe and for Pipe-Arch

and Structural Plate Pipe

Shall meet the requirements of AASHTO M 197 (ASTM B 744M)

Shall meet the requirements of AASHTO M 167 (ASTM B 761M), and M 246M ( ASTM A742M)

Table A12-10. Mechanical Properties - Corrugated Aluminum and Steel Plate

964


Shall meet the requirements of AASHTO M 219 (ASTM B 746M) Alloy 5052

Shall meet the requirements of AASHTO M 167 (ASTM B 761M)

Table A12-11-PE- Corrugated Pipes (AASHTO M 294)

* These sizes are covered in AASHTO Provisional Standard Specification for Corrugated Polyethylene Pipe, AASHTO Designation MP6-95.

Table A12-12- PE Ribbed Pipes (ASTM Figure 894)

965



Table A12-13. PVC Profile Wall Pipes (AASHTO M 304)

967


Section 13 - Railings

13.1. SCOPE

This section applies to railings for new bridges and for rehabilitated bridges to the extent that railing replacement is determined to be appropriate.

This section provides five bridge railing containment levels and their associated design requirements. Guidance for determining the level appropriate to the more common types of bridge sites is provided.

13.2. DEFINITIONS

Barrier Curb - A platform or block used to separate a raised pedestrian and/or bicycle sidewalk above the roadway level; see Figure 13.7.1-1.

Bicycle Railing - A railing or fencing system, as illustrated in Figure 13.9.3-1, that provides a physical guide for bicyclists crossing bridges to minimize the likelihood of a bicyclist falling over the system.

Bridge Approach Railing - A roadside guardrail system preceding the structure and attached to the bridge rail system that is intended to prevent a vehicle from impacting the end of the bridge railing or parapet.

Combination Railing - A bicycle or pedestrian railing system, as illustrated in Figures 13.8.2-1 and 13.9.3-1, added to a bridge vehicular railing or barrier system.

Concrete Barrier - A railing system of reinforced concrete having a traffic face that usually but not always adopts some form of a safety shape.

Concrete Parapet - A railing system of reinforced concrete, usually considered an adequately reinforced concrete wall.

Crash Testing of Bridge Railings - Conducting a series of full-scale impact tests of a bridge railing in order to evaluate the railing’s strength and safety performance.

Design Force - An equivalent static force that represents the dynamic force imparted to a railing system by a specified vehicle impacting a railing at a designated speed and angle.

Encroachment - An intrusion into prescribed, restrictive, or limited areas of a highway system, such as crossing a traffic lane or impacting a barrier system.

968


Also, the occupancy of highway right-of-way by nonhighway structures or objects of any kind or character.

969


End Zone - The area adjacent to any open joint in a concrete railing system that requires added reinforcement.

Expressway - A controlled access arterial highway that may or may not be divided or have grade separations at intersections.

Face of the Curb - The vertical or sloping surface on the roadway side of the curb.

Freeway - A controlled access divided arterial highway with grade separations at intersections.

Longitudinal Loads - Horizontal design forces that are applied parallel to the railing or barrier system and that result from friction on the transverse loads.

Multiple Use Railing - Railing that may be used either with or without a raised sidewalk.

Owner - The authority or governmental department that is responsible for all the safety design features and functions of a bridge.

Pedestrian Railing - A railing or fencing system, as illustrated in Figure 13.8.2-1, providing a physical guidance for pedestrians across a bridge so as to minimize the likelihood of a pedestrian falling from the structure.

Post - A vertical or sloping support member of a rail system that anchors a railing element to the deck.

Rail Element - Any component that makes up a railing system. It usually pertains to a longitudinal member of the railing.

Speeds - Low/High - Vehicle velocities in km/h. Low speeds are usually associated with city or rural travel where speeds are well posted and are under 70 km/h. High speeds are usually associated with expressways or freeways where posted speeds are 80 km/h or more.

Traffic Railing - Synonymous with vehicular railing; used as a bridge or structure-mounted railing, rather than a guardrail or median barrier as in other publications.

Transverse Loads - Horizontal design forces that are applied perpendicular to a railing or barrier system.

13.3. NOTATION

970


B = out-to-out wheel spacing on an axle (mm) (13.7.3.3)

971


FL = longitudinal friction force along rail = 0.33 Ft (N) (13.7.3.3)

Ft = transverse vehicle impact force distributed over a length Lt at a height He above bridge deck (N) (13.7.3.3)

Fv = vertical force of vehicle laying on top of rail (N) (13.7.3.3)

G = height of vehicle center of gravity above bridge deck (mm) (13.7.3.3)

H = height of wall (mm) (13.7.3.4.1)

HR = height of rail (mm) (13.4)

Hw = height of wall (mm) (13.4)

L = post spacing of single span (mm) (13.7.3.4.2)

Lc = critical length of wall failure (mm) (13.7.3.4.1)

LL = longitudinal length of distribution of friction force FL, LL = Lt (mm) (13.7.3.3)

Lt = longitudinal length of distribution of impact force Ft along the railing located a height of the He above the deck (mm) (13.7.3.3)

Lv = longitudinal distribution of vertical force Fv on top of railing (mm) (13.7.3.3)

= length of vehicle impact load on railing or barrier taken as L t, Lv, or LL, as appropriate (mm) (13.7.3.4.1)

Mb = ultimate moment capacity of beam at top of wall (Nmm) (13.7.3.4.1)

Mc = ultimate flexural resistance of wall about horizontal axis (Nmm/mm) (13.7.3.4.1)

Md = deck overhang moment (Nmm/mm) (13.7.3.5.3a)

Mp = plastic or yield line resistance of rail (Nmm) (13.7.3.4.2)

Mw = ultimate flexural resistance of wall about vertical axis (Nmm/mm) (13.7.3.4.1)

Pp = ultimate load resistance of a single post (N) (13.7.3.4.2)

= sum of horizontal components of rail strengths (N) (13.7.3.3)

W = weight of vehicle corresponding to the required test level, from Table 13.7.2-1 (N) (13.7.2)

972


Wb = width of base plate or distribution block (mm) (13.7.3.5.3a)

X = length of overhang from face of support to exterior girder or web (mm) (13.7.3.5.3a)

= height of R above bridge deck (mm) (13.7.3.3)

= resistance factor for the strength limit state specified in Sections 5 and 6 or for the extreme event limit state specified in Section 1 (13.7.3.5.3b)

13.4. GENERAL

The Owner shall determine the containment level of the railing appropriate to the bridge site.

Railings shall be provided along the edges of structures for protection of traffic and pedestrians. Railings may be required on bridge-length culverts.

A pedestrian walkway may be separated from an adjacent roadway by a barrier curb, traffic railing, or combination railing, as indicated in Figure 1. On high-speed roads where a pedestrian walkway is provided, the walkway area should be separated from the adjacent roadway by a traffic railing or combination railing.

973


Figure 13.4-1 - Pedestrian Walkway

Where required by the Owner, new bridge railings and the attachment to the deck overhang shall be crash tested to confirm that they meet the structural and geometric requirements of a specified railing containment level using the test criteria specified in Article 13.7.2.

13.5. MATERIALS

The requirements of Sections 5 and 6 shall apply to the materials employed in a railing system, unless otherwise modified herein.



The strength limit states shall apply using the applicable load combinations in Table 3.4.1-1 and the loads specified herein. The resistance factors for post and railing components shall be as specified in Articles 5.5.4 and 6.5.4.

Design loads for pedestrian railings shall be as specified in Article 13.8.2. Design loads for bicycle railings shall be as specified in Article 13.9.3. Pedestrian or bicycle loadings shall be applied to combination railings as specified in Article 13.10.3. Deck overhangs shall be designed for applicable strength load combinations specified in Table 3.4.1-1.

974


13.6.2. Extreme Event Limit State

The forces to be transmitted from the bridge railing to the bridge deck may be determined from an ultimate strength analysis of the railing system using the loads given in Article 13.7.3.3. Those forces shall be considered to be the factored loads at the extreme event limit state.

13.7. TRAFFIC RAILING

13.7.1. Railing System

13.7.1.1. General

The primary purpose of traffic railings shall be to contain and redirect vehicles using the structure. Consideration should be given to:

Protection of the occupants of a vehicle in collision with the railing,

Protection of other vehicles near the collision,

Protection of persons and property on roadways and other areas underneath the structure,

Railing cost-effectiveness, and

Appearance and freedom of view from passing vehicles.

A combination railing, conforming to the dimensions given in Figures 13.8.2-1 and 13.9.3-1, may be considered acceptable for use with sidewalks having widths 1000 mm or greater and curb heights up to 200 mm.

Use of the combination vehicle-pedestrian railing shown in Figure 1 shall be restricted to roads designated for 70 km/h or less.

975


Figure 13.7.1.1-1 - Typical Raised Sidewalk

13.7.1.2. Approach railings

An approach guardrail system should be provided at the beginning of all bridge railings in high-speed rural areas.

A bridge approach railing system should include a transition from the guardrail system to the rigid bridge railing system that is capable of providing lateral resistance to an errant vehicle. The approach guardrail system shall have a suitable end terminal at its nosing.

13.7.1.3. End treatment

In high-speed rural areas, the approach end of a parapet or railing shall have a suitable configuration or be shielded by a traffic barrier.

13.7.2. Containment Level Selection Criteria

One of the following containment levels should be specified:

L1 - taken to be generally acceptable for work zones with low posted speeds and very low volume, low-speed local streets;

L2 - taken to be generally acceptable for work zones and most local and collector roads with favorable site conditions as well as work zones and where a small number of heavy vehicles is expected and posted speeds are reduced;

L3 - taken to be generally acceptable for the majority of applications on high-speed highways with a mixture of trucks and heavy vehicles;

976


L4 - taken to be generally acceptable for applications on freeways with high-speed, high-traffic volume and a higher ratio of heavy vehicles and a highway with unfavorable site conditions; or

L5 - taken to be generally acceptable for the same applications as L4 when site conditions justify a higher level of containment.

977


It shall be the responsibility of the Owner to determine which of the containment levels is most appropriate for the bridge site.

In the event that crash testing is required by the Owner, the testing criteria for the chosen containment level should correspond to vehicle weights and speeds and angles of impact outlined in Table 1.

Table 13.7.2-1 - Bridge Railing Containment Levels and Crash Test Criteria

Vehicle Characteri

stics

Small Automobile

s

Pickup

Truck

Single-Unit Van

Truck

Van-Type Tractor-Trailers

W (kN) 7 8 20 80 220 355

B (mm) 1700 1700 2000 2300 2450 2450

G (mm) 550 550 700 1250 1630 1850

Impact angle

20 20 25 15 15 15

Level Test Speeds (km/h)

L1 50 50 50 N/A N/A N/A

L2 70 70 70 N/A N/A N/A

L3 100 100 100 80 N/A N/A

L4 100 100 100 N/A 80 N/A

L5 100 100 100 N/A N/A 80

13.7.3. Railing Design

13.7.3.1. General

978


A traffic railing should normally provide a smooth continuous face of rail on the traffic side. Steel posts with rail elements should be set back from the face of rail. Structural continuity in the rail members and anchorages of ends should be considered.

13.7.3.1.1. Application of Previously Tested Systems

A railing system that has been shown to be satisfactory by previous full-scale crash tests may be used without further analysis and/or testing, provided that the proposed installation does not have features that are absent in the tested configuration and that might detract from the performance of the tested railing system.

979


13.7.3.1.2. New Systems

New railing systems shall be designed in accordance with Article 13.7.3, supplemented by crash testing where required by the Owner.

13.7.3.2. Geometry and anchorages

13.7.3.2.1. Height of Traffic Parapet or Railing

Concrete railings designed with sloping traffic faces shall be at least 810 mm in height. The bottom 75 mm lip of the safety shape shall not be increased for future overlay considerations. The minimum height of the concrete wall in a concrete parapet with a vertical face shall be 685 mm.

The minimum height of the pedestrian or bicycle railing should be measured above the surface of the sidewalk or bikeway.

The minimum geometric requirements for combination railings shall be taken as specified in Article 13.8, Article 13.9, and Article 13.10.

l 3.7.3.2.2. Separation of Rail Elements

For traffic railings, the criteria for maximum opening between rails, C, and the total width of the rail(s), A, for various values of post setback distance, S, shall be as given in Table 1. The definition of these parameters for typical railings is illustrated in Figure 1.

980


Table 13.7.3.2.2-1 - Rail Separation and Width Criteria

S (mm)

C (mm) A/H

Absolute maximu

m

Desirable

maximum

Absolute minimum

Desirable

minimum

0

25

50

75

100

125

150

250

300

325

325

325

350

380

250

265

285

300

300

300

300

0.75

0.65

0.52

0.40

0.30

0.30

0.30

0.80

0.80

0.80

0.70

0.60

0.50

0.45

Figure 13.7.3.2.2-1 - Typical Traffic Railings

981


For combination and pedestrian railings, the maximum clear vertical opening between adjacent rails or post shall be as specified in Sections 13.8, 13.9, and 13.10.

l 3.7.3.2.3. Anchorages

The yield strength of anchor bolts for steel railings shall be fully developed by bond, hooks, attachment to embedded plates, or any combination thereof. Reinforcing steel for concrete barriers shall have embedment length sufficient to develop the yield strength.

13.7.3.3. Traffic railing design forces

Unless modified herein, the extreme event limit state and the corresponding load combinations in Table 3.4.1-1 shall apply.

982


Railing design forces and geometric criteria shall be as specified in Table 1 and illustrated in Figure 1. The transverse and longitudinal loads given in Table 1 need not be applied in conjunction with vertical loads.

Railings shall be proportioned such that:

(l 3.7.3.3-1)

(l 3.7.3.3-2)

for which:

= Ri (l 3.7.3.3-3)

(13.7.3.3-4)

where:

Ri = resistance of the rail (N)

Yi = distance from bridge deck to the ith rail (mm)

Table 13.7.3.3-1 - Design Forces for Traffic Railings

Design Forces and Designatio

ns

Railing Containment Levels

L1 L2 L3 L4 L5

Ft Transverse (kN)

60 120 240 516 550

FL Longitudinal (kN)

20 40 80 173 183

Fv Vertical (kN)

20 20 80 222 355

Lt and LL (mm)

1220 1220 1070 2440 2440

Lv (mm) 5500 5500 5500 12200 12200

983


He (mm) 460 510 810 1020 1070

Minimum H – Height of Railing (mm)

810 810 810 1020 1370

Figure 13.7.3.3-1 - Bridge Railing Design Forces, Vertical Location and Distribution Length

All forces shall be applied to the longitudinal rail elements. The distribution of longitudinal loads to posts shall be consistent with the continuity of rail elements. Distribution of transverse loads shall be consistent with the assumed failure mechanism of the railing system.

13.7.3.4. Design procedure for railings

13.7.3.4.1. Concrete Railings

Yield line analysis and strength design for reinforced concrete and prestressed concrete barriers or parapets may be used.

The nominal railing resistance to transverse load, Rw, may be determined using a yield line approach as:

For impacts within a wall segment:

Rw = (13.7.3.4.1-1)

The critical wall length over which the yield line mechanism occurs, Lc, shall be taken as:

984


Lc = (13.7.3.4.1-2)

For impacts at end of wall or at joint:

Rw = (13.7.3.4.1-3)

Lc = (13.7.3.4.1-4)

where:

Ft = transverse force specified in Table l3.7.3.3-1 assumed to be acting at top of concrete wall (N)


Lc = critical length of yield line failure pattern (mm)

Lt = longitudinal length of distribution of impact force Ft (mm)

Rw = total transverse resistance of the railing (N)

985


Mb = additional flexural resistance of beam in addition to Mw, if any, at top of wall (Nmm)

Mw = flexural resistance of a wall (Nmm/mm)

Mc = flexural resistance of cantilevered wall specified in Article l 3.7.3.5.2 (Nmm/mm)

For use in the above equations, Mc and Mw should not vary significantly over the height of the wall. For other cases, a rigorous yield line analysis should be used.

13.7.3.4.2. Post-and-Beam Railings

Inelastic analysis shall be used for design of post-and-beam railings under failure conditions. The critical wall nominal resistance, R, shall be taken as the least value determined from Equations 1 and 2 for various numbers of railing spans, N.

For failure modes involving an odd number of railing spans, N:

R = (13.7.3.4.2-1)

For failure modes involving an even number of railing spans, N:

R = (13.7.3.4.2-1)

L = post spacing or single-span (mm)

Mp = inelastic or yield line resistance of all of the rails contributing to a plastic hinge (Nmm)

Pp = ultimate transverse load resistance of a single post located above the deck (N)

R = total ultimate resistance, i.e., nominal resistance, of the railing (N)

Lt,LL= transverse length of distributed vehicle impact loads, Ft and FL (mm)

l 3.7.3.4.3. Combination Concrete Parapet and Metal Rail

986


The resistance of each component of a combination bridge rail shall be determined as specified in Articles 13.7.3.4.l and 13.7.3.4.2. The flexural strength of the rail shall be determined over one span, RR, and over two spans, R/

R . The resistance of the post on top of the wall, PP, including the resistance of the anchor bolts or post, shall be determined.

The resistance of the combination parapet and rail shall be taken as the lesser of the resistances determined for the two failure modes shown in Figures 1 and 2.

987


Figure 13.7.3.4.3-1 - Combination Concrete Wall and Metal Rail - Impact at Midspan of Rail

988


Figure 13.7.3.4.3-2 - Combination Concrete Wall and Metal Rail – Impact at Post

989


Where the vehicle impact is at midspan of the metal rail, as illustrated in Figure 1, the flexural resistance of the rail, RR , and the maximum strength of the concrete wall, Rw , shall be added together to determine the combined resultant strength, , and the effective height, , taken as:

= RR + Rw (13.7.3.4.3-1)

= (13.7.3.4.3-2)

RR = ultimate capacity of rail over one span (N)

Rw = ultimate capacity of wall as specified in Article 13.7.3.4.1 (N)

Hw = height of wall (mm)

HR = height of rail (mm)

Where the vehicle impact is at a post, as illustrated in Figure 2, the maximum resultant strength, , shall be taken as the sum of the post capacity, PP , the rail strength, R’

R , and a reduced wall strength, Rw , located at a height .

(13.7.3.4.3-3)

(13.7.3.4.3-4)

for which:

(13.7.3.4.3-5)

where:

Pp = ultimate transverse resistance of post (N)

= ultimate transverse resistance of rail over two spans (N)

Rw = ultimate transverse resistance of wall as specified in Article 13.7.3.4.1 (N)

990


= capacity of wall, reduced to resist post load (N)

13.7.3.5. Deck overhang design

13.7.3.5.1. Design Cases

Bridge deck overhangs shall be designed for the following design cases considered separately:

991


Design Case 1: the transverse and longitudinal forces specified in Article 13.7.3.3 - extreme event limit state

Design Case 2: the vertical forces specified in Article 13.7.3.3 - extreme event limit state

Design Case 3: the loads, specified in Article 3.6.1, that occupy the overhang - strength limit state

Unless a lesser thickness can be proven satisfactory by crash testing, the minimum edge thickness for concrete deck overhangs shall be taken as:

For concrete deck overhangs supporting a deck-mounted post system: 200 mm

For a side-mounted post system: 300 mm

For concrete deck overhangs supporting concrete parapets or barriers: 200 mm

13.7.3.5.2. Decks Supporting Concrete Parapet Railings

For Design Case 1, the deck overhang may be designed to provide a flexural resistance, Ms , in Nmm/mm which, acting coincident with the tensile force T in N/mm, specified herein, exceeds Mc of the parapet. The axial tensile force, T, may be taken as:

(13.7.3.5.2-1)

where:

Rw = parapet resistance specified in Article 13.7.3.4.1 (N)

Lc = critical length of yield line failure pattern (mm)


T = tensile force per unit of deck length (N/mm)

Design of the deck overhang for the vertical forces specified in Design Case 2 shall be based on the overhanging portion of the deck.

992


13.7.3.5.3. Decks Supporting Post-and-Beam Railings

13.7.3.5.3a. Overhang Design

For Design Case l, the moment per mm, Md , and thrust per mm of deck, T, may be taken as:

Md = (13.7.3.5.3a-1)

T = (13.7.3.5.3a-2)

For Design Case 2, the punching shear force and overhang moment may be taken as:

Pv = (13.7.3.5.3a-3)

Md = (13.7.3.5.3a-4)

for which:

b = 2X + Wb L (13.7.3.5.3a-5)

where:

Mpost = flexural resistance of railing post (N)

Pp = shear corresponding to Mpost (N)

X = distance from the outside edge of the post base plate to the section under investigation, as

specified in Figure 1 (mm)

Wb = width of base plate (mm)

993


T = tensile force in deck (N/mm)

D = distance from the outer edge of the base plate to the innermost row of bolts, as shown in Figure 1 (mm)

L = post spacing (mm)

Lv = longitudinal distribution of vertical force Fv on top of railing (mm)

Fv = vertical force of vehicle laying on top of rail after impact forces F t and FL are over (N)

994


Figure 13.7.3.5.3a-1 - Effective Length of Cantilever for Carrying Concentrated Post Loads,

Transverse or Vertical

13.7.3.5.3b. Resistance to Punching Shear

For Design Case 1, the factored shear may be taken as:

Vu = Af Fy (13.7.3.5.3b-1)

The factored resistance of deck punching shear may be taken as:

Vr = Vn (13.7.3.5.3b-2)

Vn = Vc (13.7.3.5.3b-3)

Vc = 0.332 (13.7.3.5.3b-

4)

(13.7.3.5.3b-5)

995


for which:

where:

h = depth of slab (mm)

Wb = width of base plate (mm)

Af = area of post compression flange (mm2)

Fy = yield strength of post compression flange (MPa)

b = length of deck resisting post strength or shear load = h + Wb

996


B = distance between centroids of tensile and compressive stress resultants in post (mm)

D = depth of base plate (mm)

E = distance from edge of slab to centroid of compressive stress resultant in post (mm)

f/c = 28-day compressive strength of concrete (MPa)

= resistance factor = 1.0

The assumed distribution of forces for punching shear shall be as shown in Figure 1.

Figure 13.7.3.5.3b-1 - Punching Shear Failure Mode

13.8. PEDESTRIAN RAILING

13.8.1. Geometry

997


The minimum height of a pedestrian railing shall be 1060 mm measured from the top of the walkway.

998


A pedestrian rail may be composed of horizontal and/or vertical elements. The clear opening between rail elements shall not exceed 150 mm.

When both horizontal and vertical elements are used, the 150 mm clear opening shall apply to the lower 685 mm of the railing, and the spacing in the upper portion shall not be greater than 380 mm or as shown in Table 13.7.3.2.2-1. A safety toe rail or curb should be provided.

The rail spacing requirements given above should not apply to chain link or metal fabric fence support rails and posts. Mesh size of chain link or metal fabric fence should have openings no larger than 50 mm.

13.8.2. Design Live Loads

The design live loading for pedestrian railing shall be w = 0.73 N/mm, both transversely and vertically, acting simultaneously on each longitudinal element. A railing member shall also be designed for a concentrated load of 890 N, which may act simultaneously with the above loads at any point and in any direction at the top of the rail.

The design load for chain link or metal fabric fence shall be 7.2 x l0-4 MPa acting normal to the entire surface.

The application of loads shall be as indicated in Figure 1, in which the shapes of rail members are illustrative only. Any material or combination of materials specified in Article 13.5 may be used.

999


Figure 13.8.2-1 - Pedestrian Railing Loads - To be used on the outer edge of a sidewalk when

highway traffic is separated from pedestrian traffic by a traffic railing- Railing shape illustrative only.

1000


13.9. BICYCLE RAILINGS

13.9.1. General

Bicycle railings shall be used on bridges specifically designed to carry bicycle traffic and on bridges where specific protection of bicyclists is deemed necessary.

13.9.2. Geometry

The height of a bicycle railing shall not be less than 1370 mm, measured from the top of the riding surface. The height of the upper and lower zones of a bicycle railing shall be at least 685 mm. The upper and lower zones shall have rail spacing satisfying the respective provisions of Article 13.8.1. If screening, fencing, or a solid face is utilized, the number of rails may be reduced.


If the rail height exceeds 1370 mm above the riding surface, design loads shall be determined by the Designer. The design loads for the lower 1370 mm of the bicycle railing shall not be less than those specified in Article 13.8.2.

The application of loads shall be as indicated in Figure 1. Any material or combination of materials specified in Article 13.5 may be used.

Figure 13.9.3-1 - Bicycle Railing Loads - To be used on the outer edge of a bikeway when

1001


highway traffic is separated from bicycle traffic by a traffic railing- Railing shape illustrative only.

1002


13.10. COMBINATION RAILINGS

13.10.1. General

The combination railing shall conform to the requirements of either the pedestrian or bicycle railings, as specified in Section 13.8 and 13.9, whichever is applicable. The traffic railing portion of the combination railing shall conform to Section 13.7.

13.10.2. Geometry

The geometric provisions of Articles 13.7, 13.8, and 13.9 shall apply to their respective portions of a combination railing.


Design loads, specified in Sections 13.8 and 13.9, shall not be applied simultaneously with the vehicular impact loads.

13.11. CURBS AND SIDEWALKS

13.11.1. General

Horizontal measurements of roadway width shall be taken from the bottom of the face of the curb. A sidewalk curb located on the highway traffic side of a bridge railing shall be considered an integral part of the railing and shall be included in any crash testing.

13.11.2 Sidewalks

When curb and gutter sections with sidewalks are used on roadway approaches, the curb height for raised sidewalks on the bridge should be no more than 200 mm. If a barrier curb is required, the curb height should not be less than 150 mm. If the height of the curb on the bridge differs from that off the bridge, it should be uniformly transitioned over a distance greater than or equal to 20 times the change in height.

13.11.3 . End Treatment of Separation Railing

The end treatment of any traffic railing or barrier shall meet the requirements specified in Sections 13.7.1.2 and 13.7.1.3.

1003


Section 14 - Joints and Bearings

14.1. SCOPE

This section contains requirements for the design and selection of structural bearings and deck joints.

Units used in this section shall be taken as N, mm, RAD, 0C, and Shore Hardness, unless otherwise noted.

14.2. DEFINITIONS

Bearing - A structural device that transmits loads while facilitating translation and/or rotation.

Bearing Joint - A deck joint provided at bearings and other deck supports to facilitate horizontal translation and rotation of abutting structural elements. It may or may not provide for differential vertical translation of these elements.

Bronze Bearing - A bearing in which displacements or rotations take place by the sliding of a bronze surface against a mating surface.

CDP - Cotton-Duck-Reinforced Pad - A pad made from closely spaced layers of elastomer and cotton-duck, bonded together during vulcanization.

1004


Closed Joint - A deck joint designed to prevent the passage of debris through the joint and to safeguard pedestrian and cycle traffic.

Construction Joint - A temporary joint used to permit sequential construction.

Cycle-Control Joint - A transverse approach slab joint designed to permit longitudinal cycling of integral bridges and attached approach slabs.

Deck Joint - A structural discontinuity between two elements, at least one of which is a deck element. It is designed to permit relative translation and/or rotation of abutting structural elements.

Disc Bearing - A bearing that accommodates rotation by deformation of a single elastomenc disc molded from a urethane compound. It may be movable, guided, unguided, or fixed. Movement is accommodated by sliding of polished stainless steel on PFTE.

Double Cylindrical Bearing - A bearing made from two cylindrical bearings placed on top of each other with their axes at right angles to facilitate rotation about any horizontal axis.

Fiberglass-Reinforced Pad (FGP) - A pad made from discrete layers of elastomer and woven fiberglass bonded together during vulcanization.

Fixed Bearing - A bearing that prevents differential longitudinal translation of abutting structural elements. It may

1005


or may not provide for differential lateral translation or rotation.

1006


Integral Bridge - A bridge without deck joints.

Joint - A structural discontinuity between two elements. The structural members used to frame or form the discontinuity.

Joint Seal - A poured or preformed elastomeric device designed to prevent moisture and debris from penetrating joints.

Knuckle Bearing - A bearing in which a concave metal surface rocks on a convex metal surface to provide rotation capability about any horizontal axis.

Longitudinal - Parallel with the main span direction of a structure.

Longitudinal Joint - A joint parallel to the span direction of a structure provided to separate a deck or superstructure into two independent structural systems.

Metal Rocker or Roller Bearing - A bearing that carries vertical load by direct contact between two metal surfaces and that accommodates movement by rocking or rolling of one surface with respect to the other.

Movable Bearing - A bearing that facilitates differential horizontal translation of abutting structural elements in a longitudinal and/or lateral direction. it may or may not provide for rotation.

1007


Multirotational Bearing - A bearing consisting of a rotational element of the pot type, disc type, or spherical type when used as a fixed bearing and that may, in addition, have sliding surfaces to accommodate translation when used as an expansion bearing. Translation may be constrained to a specified direction by guide bars.

Neutral Point - The point about which all of the cyclic volumetric changes of a structure take place.

Open Joint - A joint designed to permit the passage of water and debris through the joint.

Plain Elastomeric Pad (PEP) - A pad made exclusively of elastomer, which provides limited translation and rotation.

Polytetrafluorethylene (PTFE) - Also known as Teflon.

Pot Bearing - A bearing that carries vertical load by compression of an elastomeric disc confined in a steel cylinder and that accommodates rotation by deformation of the disc.

PTFE Sliding Bearing - A bearing that carries vertical load through contact stresses between a PTFE sheet or woven fabric and its mating surface, and that permits movements by sliding of the PTFE over the mating surface.

Relief Joint - A deck joint, usually transverse, that is designed to minimize either unintended composite action or the effect of differential horizontal movement between a deck and its supporting structural system.

1008


Rotation about the Longitudinal Axis - Rotation about an axis parallel to the main span direction of the bridge.

1009


Rotation about the Transverse Axis - Rotation about an axis parallel to the transverse axis of the bridge.

Sealed Joint - A joint provided with a joint seal.

Sliding Bearing - A bearing that accommodates movement by translation of one surface relative to another.

Steel-reinforced Elastomeric Bearing - A bearing made from alternate laminates of steel and elastomer bonded together during vulcanization. Vertical loads are carried by compression of the elastomer. Movements parallel to the reinforcing layers and rotations are accommodated by deformation of the elastomer.

Translation - Horizontal movement of the bridge in the longitudinal or transverse direction.

Transverse - The horizontal direction normal to the longitudinal axis of the bridge.

Waterproofed Joints - Open or closed joints that have been provided with some form of trough below the joint to contain and conduct deck discharge away from the structure.

14.3 NOTATION

A = plan area of elastomeric element or bearing (mm2) (14.6.3.1)B = length of pad if rotation is about its transverse axis or

1010


width of pad if rotation is about its

longitudinal axis (mm) (14.7.5.3.5)c = design clearance between piston and pot (mm) (14.7.4.7)D = diameter of the projection of the loaded surface of the bearing in the horizontal plane (mm);

diameter of pad (mm) (14.7.3.2) (14.7.5.3.5)Dd = diameter of disc element (mm) (14.7.8.1) (14.7.8.5)Dp = internal pot diameter in pot bearing (mm) (14.7.4.3)D1 = diameter of curved surface of rocker or roller unit (mm) (14.7.1.4)D2 = diameter of curved surface of mating unit (D2 = for a flat plate) (mm) (14.7.1.4)Ec = effective modulus of elastomeric bearing in compression (MPa) (14.6.3.2)Es = Young’s modulus for steel (MPa) (14.7.1.4)Fy = specified minimum yield strength of the weakest steel at the contact surface (MPa)

(14.7.1.4)G = shear modulus of the elastomer (MPa) (14.6.3.1)Hs = horizontal service load on the bearing (N) (14.7.4.7)Hu = factored horizontal force on the bearing or restraint (N) (14.6.3.1)hmax = thickness of thickest elastomeric layer in elastomeric bearing (mm) (14.7.5.3.7)hp = depth of the pot (mm) (14.7.4.6)hr = depth of elastomeric disc for a pot bearing (mm) (14.7.4.3)hri = thickness of ith elastomeric layer in elastomeric bearing (mm) (14.7.5.1)hrt = total elastomer depth in an elastomeric bearing (mm) (14.6.3.1)hs = thickness of steel laminate in steel-laminated elastomeric bearing (mm) (14.7.5.3.7)I = moment of inertia (mm4) (14.6.3.2)L = length of a rectangular elastomeric bearing (parallel to longitudinal bridge axis) (mm);

projected length of the sliding surface perpendicular to the rotation axis (mm) (14.7.5.1)

1011


(14.7.3.3)

1012


Mu = factored moment (N.mm) (14.6.3.2)n = number of layers of elastomer (14.7.5.3.5)PD = service compressive load due to permanent loads (N) (14.7.3.3)Pr = factored resistance of pot wall (N) (14.7.4.6)Ps = service compressive load due to total load (N) (14.7.1.4)Pu = factored compressive force (N) (14.6.3.1)R = radius of curved sliding surface (mm) (14.6.3.2)r = length of pad if rotation is about its transverse axis or width of pad if rotation is about its

longitudinal axis (mm) (14.7.5.3.5)S = shape factor of thickest layer of an elastomeric bearing (14.7.5.1)tw = pot wall thickness (mm) (14.7.4.6)W = width of roadway gap (mm); width of the bearing in the transverse direction (mm);

length of cylinder (mm) (14.5.3.2) (14.7.1.4) (14.7.3.2)w = height of piston rim in pot bearing (mm) (14.7.4.7) = effective friction angle in PTFE bearings (RAD) (14.7.3.3) FTH = constant amplitude fatigue threshold for Category A (MPa) (14.7.5.3.7) o = maximum horizontal displacement of the bridge deck at the service limit state (mm)

(14.7.5.3.4) s = maximum shear deformation of the elastomer at the service limit state (mm) (14.7.5.3.4) u = maximum factored shear deformation of the elastomer (mm) (14.6.3.1) = instantaneous compressive deflection of bearing (mm) (14.7.5.3.3)

i = instantaneous compressive strain in ith elastomer layer of a laminated bearing

(14.7.5.3.3)s = maximum service rotation due to total load (RAD)

(14.7.5.3. 5)

1013


s ,x = service rotation due to total load about transverse axis (RAD) (14.7.6.3.5)

s , z = service rotation due to total load about longitudinal axis (RAD) (14.7.6.3.5)

u = factored or design rotation (RAD) (14.4.2)

= skew angle of bridge or deck joint (DEG) (14.5.3.2)

= coefficient of friction (14.6.3.1)

L = service average compressive stress due to live load (MPa) (14.7.5.3.2)

s = service average compressive stress due to total load (MPa) (14.7.5.3.2)

SS = maximum average contact stress at the strength limit state permitted on PTFE by Table

14.7.2.4-1

or on bronze by Table 14.7.7.3-1 (MPa) (14.7.3.2)

u = factored average compressive stress (MPa) (14.7.3.2)


14.4. MOVEMENTS AND LOADS

14.4.1. General

The selection and layout of the joints and bearings shall allow for deformations due to temperature and other time-dependent causes and shall be consistent with the proper functioning of the bridge.

1014


Deck joints and bearings shall be designed to resist loads and accommodate movements at the service and strength limit states and to satisfy the requirements of the fatigue and fracture limit state. The loads induced on the joints, bearings, and structural members depend on the stiffness of the individual elements and the tolerances achieved during fabrication and erection. These influences shall be taken into account when calculating design loads for the elements. No damage due to joint or bearing movement shall be permitted at the service limit state, and no irreparable damage shall occur at the strength limit or extreme event states.

Translational and rotational movements of the bridge shall be considered in the design of bearings. The sequence of construction shall be considered, and all critical combinations of load and movement shall be considered in the design. Rotations about two horizontal axes and the vertical axis shall be considered. The movements shall include those caused by the loads, deformations, and displacements caused by creep, shrinkage and thermal effects, and inaccuracies in installation. In all cases, both instantaneous and long-term effects shall be considered, but the influence of impact need not be included. The most adverse combination shall be tabulated in a rational form such as shown in Figure l.

For determining force effects in joints, bearings, and adjacent structural elements, the influence of their stiffnesses and the expected tolerances achieved during fabrication and erection shall be considered.

The three-dimensional effects of translational and rotational movements of the bridge shall be considered in the design of bearings.

Both instantaneous and long-term effects shall be considered in the design of joints and bearings.

1015


Figure 14.4.1-1 – Typical Bridge Bearing Schedule

Brigde name or ref

Bearing indentification mark

Number of bearings required

Seating material Upper surface

Lower surface

Allowable average contact pressure (MPa)

Upper face Serviceability

Strength

Lower face Serviceability

Srengh

Design load effects (N)

Service limit state Vertical

max.

perm.

min.

Strength limit state Transverse

Longitudinal

Vertical

Translation Service limit state

Irreversible Transcverse

Longitudinal

Reversible Transcverse

Longitudinal

Strenght limit state


Longitudinal


1016


Longitudinal

Rotation (RAD)

Service limit state


Longitudinal


Longitudinal

Maximum bearing dimensions (mm)

Upper surface Transcverse

Longitudinal

Lower surface Transcverse

Longitudinal

Overall heigh

Tolerable movement of bearing under transient loads (mm)

Vertical

Transcverse

Longitudinal

Allowable resistance to translation under service limit state (N)

Transcverse

Longitudinal

Allowable resistance to rotation under service limit state (N/mm)

Transcverse

Longitudinal

Type of attachment to structure and substructure

Transcverse

Longitudinal

1017


14.4.2. Design Requirements

The minimum thermal movements shall be computed from the extreme temperature specified in Article 3.12.2 and the estimated setting temperatures. Design loads shall be based on the load combinations and load factors specified in Section 3.

The maximum unfactored service rotation due to total load, s ,

for bearings such as elastomeric pads or steel-reinforced elastomeric bearings that do not achieve hard contact between metal components shall be taken as the sum of:

The dead and live load rotations, and

An allowance for uncertainties, which shall be taken as 0.005 RAD unless an approved quality control plan justifies a smaller value.

The strength limit state rotation, , for bearings such as pot bearings, disc bearings, and curved sliding surfaces that may develop hard contact between metal components shall be taken as the sum of:

The rotations due to all applicable factored loads;

The maximum rotation caused by fabrication and installation tolerances, which shall be taken as 0.01 RAD unless an approved quality control plan justifies a smaller value; and

An allowance for uncertainties, which shall be taken as 0.01 RAD unless an approved quality control plan justifies a smaller value.

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14.5. BRIDGE JOINTS

14.5.1. Requirements

14.5.1.1. GENERAL

Deck joints shall consist of components arranged to accommodate the translation and rotation of the structure at the joint.

The type of joints and surface gaps shall accommodate the movement of motorcycles, bicycles, and pedestrians, as required, and shall neither significantly impair the riding characteristics of the roadway nor cause damage to vehicles.

The joints shall be detailed to prevent damage to the structure from water and roadway debris.

Longitudinal deck joints shall be provided only where necessary to modify the effects of differential lateral and/or vertical movement between the superstructure and substructure.

Joints and joint anchors for orthotropic deck superstructures require special details.

14.5.1.2. STRUCTURAL DESIGN

Joints and their supports shall be designed to withstand factored force effects over the factored range of movements, as

1019


specified in Section 3. Resistance factors and modifiers shall be taken as specified in Sections 1, 5 and 6, as appropriate.

1020


The following factors shall be considered in determining force effects and movements:

Properties of materials in the structure, including coefficient of thermal expansion, modulus of

elasticity, and Poisson’s ratio;

Effects of temperature, creep, and shrinkage;

Sizes of structural components;

Construction tolerances;

Method and sequence of construction;

Skew and curvature;

Resistance of the joints to movements;

Approach pavement growth;

Substructure movements due to embankment construction;

Foundation movements associated with the consolidation and stabilization of subsoils;

Structural restraints; and

Static and dynamic structural responses and their interaction.

The length of superstructure affecting the movement at one of its joints shall be the length from the joint being considered to the structure’s neutral point.

For a curved superstructure that is laterally unrestrained by guided bearings, the direction of longitudinal movement at a bearing joint may be assumed to be parallel to the chord of the deck centerline taken from the joint to the neutral point of the structure.

1021


The potential for unaligned longitudinal and rotational movement of the superstructure at a joint should be considered in designing the vertical joints in curbs and raised barriers and in determining the appropriate position and orientation of closure or bridging plates.

14.5.1.3. GEOMETRY

The moving surfaces of the joint shall be designed to work in concert with the bearings to avoid binding the joints and adversely affecting force effects imposed on bearings.

14.5.1.4 . MATERIALS

The materials shall be selected so as to ensure that they are elastically, thermally, and chemically compatible. Where substantial differences exist, material interfaces shall be formulated to provide fully functional systems.

Materials, other than elastomers, should have a service life of not less than 100 years. Elastomers for joint seals and troughs should provide a service life not less than 25 years.

Joints exposed to traffic should have a skid-resistant surface treatment, and all parts shall be resistant to attrition and vehicular impact.

14.5.1.5. MAINTENANCE

Deck joints shall be designed to operate with a minimum of

1022


maintenance for the design life of the bridge.

1023


Detailing should permit access to the joints from below the deck and provide sufficient area for maintenance.

Mechanical and elastomeric components of the joint shall be replaceable.

Joints shall be designed to facilitate vertical extension to accommodate roadway overlays.

14.5.2. Selection

14.5.2.1. NUMBER OF JOINTS

The number of movable deck joints in a structure should be minimized. Preference shall be given to continuous deck systems and superstructures and, where appropriate, integral bridges.

The need for a fully functional cycle-control joint shall be investigated on approaches of integral bridges.

Movable joints may be provided at abutments of single-span structures exposed to appreciable differential settlement. Intermediate deck joints should be considered for multiple-span bridges where differential settlement would result in significant overstresses.

14.5.2.2. LOCATION OF JOINTS

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Deck joints should be avoided over roadways, railways, sidewalks, other public areas, and at the low point of sag vertical curves.

Deck joints should be positioned with respect to abutment backwalls and wingwalls to prevent the discharge of deck drainage that accumulates in the joint recesses onto bridge seats.

Open deck joints should be located only where drainage can be directed to bypass the bearings and discharged directly below the joint

Closed or waterproof deck joints should be provided where joints are located directly above structural members and bearings that would be adversely affected by debris accumulation.

For straight bridges, the longitudinal elements of deck joints, such as plate fingers, curb and barrier plates, and modular joint seal support beams, should be placed parallel to the longitudinal axis of the deck. For curved and skewed structures, allowance shall be made for deck end movements consistent with that provided by the bearings.

14.5.3. Design Requirements

14.5.3.1 . MOVEMENTS DURING CONSTRUCTION

Where practicable, the construction of abutments and piers located in or adjacent to embankments should be delayed until the embankments have been placed and consolidated. Otherwise, deck joints should be sized to accommodate the

1025


probable abutment and pier movements resulting from embankment consolidation after their construction.

1026


Closure pours in concrete structures may be used to minimize the effect of prestress-induced shortening on the width of seals and the size of bearings.

14.5.3.2 . MOVEMENTS IN SERVICE

A roadway surface gap, W, in mm, in a transverse deck joint, measured normal to the joint at the factored extreme movement and determined using the strength load combination specified in Table 3.4.1-1 shall satisfy:

For single gap: W 64 + 38(1 - 2sin2 )(14.5.3.2-1)

For multiple modular gaps: W 50 + 25 (1 - 2sin2 )(14.5.3.2-2)

where:

= skew of deck at the joint (DEG)

For steel superstructures, the open width of a transverse deck joint and roadway surface gap therein shall not be less than 25 mm at factored extreme movement. For concrete superstructures, consideration shall be given to the opening of joints due to creep and shrinkage that may require initial minimum openings of less than 25 mm.

Unless more appropriate criteria are available, the maximum surface gap of longitudinal roadway joints shall not exceed 25 mm.

1027


At the factored extreme movement, the opening between adjacent fingers on a finger plate shall not exceed:

50 mm for longitudinal openings greater than 200 mm, or

75 mm for longitudinal openings 200 mm or less.

The finger overlap at the factored extreme movement shall be not less than 38 mm.

Where bicycles are anticipated in the roadway, the use of special covering floor plates in shoulder areas shall be considered.

14.5.3.3. PROTECTION

Deck joints shall be designed to accommodate the effects of vehicular traffic, pavement maintenance equipment, and other long-term environmentally induced damage.

Joints in concrete decks should be armored with steel shapes, weldments, or castings. Such armor shall be recessed below roadway surfaces.

Jointed approach pavements shall be provided with pressure relief joints and/or pavement anchors. Approaches to integral bridges shall be provided with cycle control pavement joints.

1028


14.5.3.4. BRIDGING PLATES

Joint bridging plates and finger plates should be designed as cantilever members capable of supporting wheel loads.

The differential settlement between the two sides of a joint bridging plate shall be investigated. If the differential settlement cannot be either reduced to acceptable levels or accommodated in the design and detailing of the bridging plates and their supports, a more suitable joint should be used.

Rigid bridging plates shall not be used at elastomenc bearings or hangers unless they are designed as cantilever members, and the contract documents require them to be installed to prevent binding of the joints due to horizontal and vertical movement at bearings.

14.5.3.5. ARMOR

Joint-edge armor embedded in concrete substrates should be pierced by 20 mm-minimum-diameter vertical vent holes spaced on not more than 460 mm centers.

Metal surfaces wider than 300 mm that are exposed to vehicular traffic shall be provided with an antiskid treatment.

14.5.3.6. ANCHORS

Armor anchors or shear connectors should be provided to ensure composite behavior between the concrete substrate and the joint hardware and to prevent subsurface corrosion by

1029


sealing the boundaries between the armor and concrete substrate.

Anchors for roadway joint armor shall be directly connected to structural supports or extended to effectively engage the reinforced concrete substrate.

The free edges of roadway armor, more than 75 mm from other anchors or attachments, shall be provided with 12.0 mm-diameter end-welded studs not less than 100 mm long spaced at not more than 300 mm from other anchors or attachments. The edges of sidewalk and barrier armor shall be similarly anchored.

14.5.3.7. BOLTS

Anchor bolts for bridging plates, joint seals, and joint anchors shall be fully torqued high-strength bolts. The interbedding of nonmetallic substrates in connections with high-strength bolts shall be avoided. Cast-in-place anchors shall be used in new concrete. Expansion anchors, countersunk anchor bolts, and grouted anchors shall not be used in new construction.

14.5.4. Fabrication

Shapes or plates shall be of sufficient thickness to stiffen the assembly and minimize distortion due to welding.

To ensure appropriate fit and function, the contract documents should require that:

1030


Joint components be fully assembled in the shop for inspection and approval,

Joints and seals be shipped to the job-site fully assembled, and

Assembled joints in lengths up to 18 000 mm be furnished without intermediate field splices.

14.5.5. Installation

14.5.5.1. ADJUSTMENT

In the absence of more accurate information, the installation temperature shall be taken as the mean shade air temperature under the structure for the 48 hours prior to joint installation in concrete structures and for the 24 hours prior to joint installation for structures where the main members are made of steel.

For long structures, an allowance shall be included in the specified joint widths to account for the inaccuracies inherent in establishing installation temperatures and for superstructure movements that may take place during the time between the setting of the joint width and completion of joint installation. In the design of joints for long structures, preference should be given to those devices, details, and procedures that will allow joint adjustment and completion in the shortest possible time.

Connections of joint supports to primary members should allow horizontal, vertical, and rotational adjustments.

Construction joints and block outs should be used where

1031


practicable to permit the placement of backfill and the major structure components prior to joint placement and adjustment.

14.5.5.2.TEMPORARY SUPPORTS

Deck joints shall be furnished with temporary devices to support joint components in proper position until permanent connections are made or until encasing concrete has achieved an initial set. Such supports shall provide for adjustment of joint widths for variations in installation temperatures.

14.5.5.3 . FIELD SPLICES

Joint designs shall include details for transverse field splices for staged construction and for joints longer than 18 000 mm. Where practicable, splices should be located outside of wheel paths and gutter areas.

Details in splices should be selected to maximize fatigue life.

Field splices provided for staged construction shall be located with respect to other construction joints to provide sufficient room to make splice connections.

The contract documents should require that permanent seals not be placed until after joint installation has been completed. Where practicable, only those seals that can be installed in one continuous piece should be used. Where field splicing is unavoidable, splices should be vulcanized.

1032


14.5.6. Considerations for Specific Joint Types

14.5.6.1. OPEN JOINTS

Open deck joints shall permit the free flow of water through the joint. Piers and abutments at open joints shall satisfy the requirements of Article 2.5.2 in order to prevent the accumulation of water and debris.

14.5.6.2.CLOSED JOINTS

Sealed deck joints shall seal the surface of the deck, including curbs, sidewalks, medians, and, where necessary, parapet and barrier walls. The sealed deck joint shall prevent the accumulation of water and debris, which may restrict its operation. Closed or waterproof joints exposed to roadway drainage shall have structure surfaces below the joint shaped and protected as required for open joints.

Joint seals should be watertight and extrude debris when closing.

Drainage accumulated in joint recesses and seal depressions shall not be discharged on bridge seats or other horizontal portions of the structure.

Where joint movement is accommodated by a change in the geometry of elastomeric glands or membranes, the glands or membranes shall not come into direct contact with the wheels of vehicles.

1033


14.5.6.3. WATERPROOFED JOINTS

Waterproofing systems for joints, including joint troughs, collectors, and downspouts, shall be designed to collect, conduct, and discharge deck drainage away from the structure.

In the design of drainage troughs, consideration should be given to:

Trough slopes of not less than 1 mm/12 mm;

Open-ended troughs or troughs with large discharge openings;

Prefabricated troughs;

Troughs composed of reinforced elastomers, stainless steel, or other metal with durable coatings;

Stainless steel fasteners;

Troughs that are replaceable from below the joint;

Troughs that can be flushed from the roadway surface; and

Welded metal joints and vulcanized elastomenc splices.

14.5.6.4. JOINT SEALS

Seals shall accommodate all anticipated movements.

1034


In the choice of a seal type, consideration should be given to seals that:

Are preformed or prefabricated,

Can be replaced without major joint modification,

Do not support vehicular wheel loads,

Can be placed in one continuous piece,

Are recessed below joint armor surface,

Are mechanically anchored, and

Respond to joint width changes without substantial resistance.

Elastomeric material for seals should be:

Durable, of virgin neoprene or natural rubber and reinforced with steel or fabric laminates;

Vulcanized;

Verified by long-term cyclic testing; and

Connected by adhesives that are chemically cured.

14.5.6.5. POURED SEALS

Unless data supports a smaller joint width, the joint width for poured seals should be at least 6.0 times the anticipated factored joint movement.

1035


Sealant bond to metal and masonry materials should be documented by approved test methods.

14.5.6.6. COMPRESSION AND CELLULAR SEALS

Where seals with heavy webbing are exposed to the full movement range, joints shall not be skewed more than 20 o.

Compression seals for bearing joints shall not be less than 64 mm nor more than 150 mm wide when uncompressed and shall be specified in width increments in multiples of 12.0 mm.

Primary roadway seals shall be furnished without splices or cuts, unless specifically approved by the Engineer.

In gutter and curb areas, roadway seals shall be bent up in gradual curves to retain roadway drainage. Ends of roadway seals shall be protected by securely attached vented caps or covers. Secondary seals in curbs and barrier areas may be cut and bent as necessary to aid in bending and insertion into the joint.

Closed cell seals shall not be used in joints where they would be subjected to sustained compression, unless seal and adhesive adequacy have been documented by long-term demonstration tests for similar applications.

14.5.6.7. SHEET AND STRIP SEALS

1036


In the selection and application of either sheet or strip seals, consideration should be given to:

Joint designs for which glands with anchorages not exposed to vehicular loadings,

Joint designs that allow complete closure without detrimental effects to the glands,

Joint designs where the elastomeric glands extend straight to deck edges rather than being bent up

at curbs or barriers,

Decks with sufficient crown or superelevation to ensure lateral drainage of accumulated water and debris,

Glands that are shaped to expel debris, and

Glands without abrupt changes in either horizontal or vertical alignment.

Sheet and strip seals should be spliced only when specifically approved by the engineer.

14.5.6.8. PLANK SEALS

Application of plank seals should be limited to structures on secondary roads with light truck traffic, and that have unskewed or slightly skewed joints.

Consideration should be given to:

Seals that are provided in one continuous piece for the length

1037


of the joint,

Seals with splices that are vulcanized, and

Anchorages that can withstand the forces necessary to stretch or compress the seal.

14.5.6.9 . MODULAR SEALS

Consideration should be given to:

Seals that have been verified by long-term testing,

Seals with elastomeric glands recessed below the metal portions of the assembly,

Seals designed to facilitate repair and replacement of components,

Seals in urban areas that have components designed to minimize noise, and

Seals that are fully assembled by the manufacturer.

Joint geometry should be kept as simple as possible. Blockouts should be considered to permit installation of seals after the major portions of the structure have been placed.

14.6. REQUIREMENTS FOR BEARINGS

14.6.1. General

Bearings may be fixed or movable as required for the bridge

1038


design. Movable bearings may include guides to control the direction of translation. Fixed and guided bearings shall be designed to resist all loads and restrain unwanted translation.

Unless otherwise noted, the resistance factor for bearings, , shall be taken as 1.0.

Bearings subject to net uplift at any limit state shall be secured by tie-downs or anchorages.

The magnitude and direction of movements and the loads to be used in the design of the bearing shall be clearly defined in the contract documents.

Combinations of different types of fixed or movable bearings should not be used at the same expansion joint, bent, or pier, unless the effects of differing deflection and rotation characteristics on the bearings and the structure are accounted for in the design.

Multirotational bearings conforming to the provisions of this section should not be used where vertical loads are less than 20 percent of the vertical bearing capacity.

Rigid-type bearings and their components shall be designed to remain elastic during the design earthquake.

All bearings shall be evaluated for component and connection strength and bearing stability.

1039


14.6.2 Characteristics

The bearing chosen for a particular application shall have appropriate load and movement capabilities. Table 1 and Figure 1 may be used as a guide when comparing the different bearing systems.

The following terminology shall apply to Table 1:

S = Suitable

U = Unsuitable

L = Suitable for limited applications

R = May be suitable, but requires special considerations or additional elements such as

sliders or guideways

Long. = Longitudinal axis

Trans. = Transverse axis

Vert. = Vertical axis

Table 14.6.2-1 – Bearing Suitability

1040


Figure 14.6.2-1 – Common Bearing Types

1041


14.6.3. Force Effects Resulting from Restraint of Movement at the Bearing

14.6.3.1. HORIZONTAL FORCE AND MOVEMENT

Horizontal forces and moments induced in the bridge by restraint of movement at the bearings shall be determined using the movements and bearing characteristics specified in Article 14.7.

Expansion bearings and their supports shall be designed in a manner such that the structure can undergo movements to accommodate the seismic displacement determined using the provisions in Section 3 without collapse. Adequate seat width shall be provided for the expansion bearings.

The Engineer shall determine the number of bearings required to resist the loads specified in Section 3 with consideration of the potential for unequal participation due to tolerances, unintended misalignments, the capacity of the individual bearings, and the skew.

Consideration should be given to the use of field adjustable elements to provide near simultaneous engagement of the intended number of bearings.

Horizontal forces shall be taken as those induced by sliding friction, rolling friction, or shear deformation of a flexible element in the bearing.

1042


Factored sliding friction force shall be taken as:

Hu = Pu (14.6.3.1-1)

where:

Hu = factored horizontal force (N)

= coefficient of friction

Pu = factored compressive force (N)

The factored force due to the deformation of an elastomeric element shall be taken as:

Hu = GA rt

u

h

where:

G = shear modulus of the elastomer (MPa)

A = plan area of elastomeric element or bearing (mm2)

u = factored shear deformation (mm)

hrt = total depth of elastomer (mm)

Factored rolling forces shall be determined by testing.

14.6.3.2 . MOMENT

1043


Both the substructure and superstructure shall be designed for the largest factored moment, Mu, transferred by the bearing.

For curved sliding bearings without a companion flat sliding surface, Mu shall be taken as:

Mu = Pu R (14.6.3.2-1)

For curved sliding bearings with a companion flat sliding surface, Mu shall be taken as:

Mu = 2 Pu R (14.6.3.2-2)

where:

Mu = factored moment (N.mm)

R = radius of curved sliding surface (mm)

For unconfined elastomeric bearings and pads, Mu shall be taken as:

Mu = 1.60 (0.5 Ec I) rt

s

h

(14.6.3.2-3)

where:

I = moment of inertia of plan shape of bearing (mm4)

Ec = effective modulus of elastomeric bearing in compression (MPa)

s = design rotation specified in Article 14.4.2 (RAD)

hrt = total elastomer thickness (mm)

1044


14.6.4. Fabrication, Installation, Testing and Shipping

The provisions for fabrication, installation, testing, and shipping of bearings, specified in Section 818, “Bearing Devices,” of the Construction Specification, shall apply.

14.6.5. Seismic Provisions for Bearings

14.6.5.1 . GENERAL

This article shall apply to the analysis, design, and detailing of bearings to accommodate the effects of earthquakes.

These provisions shall be applied in addition to all other applicable code requirements. The bearing-type selection shall consider the seismic criteria described in Article 14.6.5.3 in the early stages of design.

14.6.5.2. APPLICABILITY

These provisions shall apply to pin, roller, rocker, and bronze or copper-alloy sliding bearings, elastomeric bearings, spherical bearings, and pot and disc bearings in common slab-on-girder bridges but not to seismic isolation-type bearings or structural fuse bearings.

Although the strategy taken herein assumes that inelastic action is confined to properly detailed hinge areas in substructure, alternative concepts that utilize movement at the

1045


bearings to dissipate seismic forces may also be considered. Where alternate strategies may be used, all ramifications of the increased movements and the predictability of the associated forces and transfer of forces shall be considered in the design and details.

14.6.5.3. DESIGN CRITERIA

The selection and the seismic design of bearings shall be related to the strength and stiffness characteristics of both the superstructure and the substructure.

Bearing design shall be consistent with the intended seismic response of the whole bridge system.

Where rigid-type bearings are used, the seismic forces from the superstructure shall be assumed to be transmitted through diaphragms or cross-frames and their connections to the bearings and then to the substructure without reduction due to local inelastic action along that load path.

Elastomeric bearings having less than full rigidity in the restrained directions, but not designed explicitly as base isolators or fuses, may be used under any circumstance. If used, they shall be designed to accommodate imposed seismic loads.

14.7. SPECIAL DESIGN PROVISIONS FOR BEARINGS

14.7.1. Metal Rocker and Roller Bearings

14.7.1.1. GENERAL

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The rotation axis of the bearing shall be aligned with the axis about which the largest rotations of the supported member occur. Provision shall be made to ensure that the bearing alignment does not change during the life of the bridge. Multiple roller bearings shall be connected by gearing to ensure that individual rollers remain parallel to each other and at their original spacing.

Metal rocker and roller bearings shall be detailed so that they can be easily inspected and maintained.

Rockers should be avoided wherever practical and, when used, their movements and tendency to tip under seismic actions shall be considered in the design and details.

14.7.1.2. MATERIALS

1047


Rocker and roller bearings shall be made of stainless steel conforming to ASTM A 240M, as specified in Article 6.4.7, or of structural steel conforming to AASHTO M 169 (ASTM A 108), M 102 (ASTM A 668M), or M 270M (ASTM A 709M), Grades 250, 345, or 345W. Material properties of these steels shall be taken as specified in Table 6.4.1-1 and Table 6.4.2-1.

14.7.1.3. GEOMETRIC REQUIREMENTS

The dimensions of the bearing shall be chosen taking into account both the contact stresses and the movement of the contact point due to rolling.

Each individual curved contact surface shall have a constant radius. Bearings with more than one curved surface shall be symmetric about a line joining the centers of their two curved surfaces.

If pintles or gear mechanisms are used to guide the bearing, their geometry should be such as to permit free movement of the bearing.

Bearings shall be designed to be stable. If the bearing has two separate cylindrical faces, each of which rolls on a flat plate, stability may be achieved by making the distance between the two contact lines no greater than the sum of the radii of the two cylindrical surfaces.

14.7.1.4. CONTACT STRESSES

At the service limit state, the contact load, Ps, shall satisfy:

1048


For cylindrical surfaces:

Ps

s

y

E

F

D

D

WD2

2

1

1

1

8

(14.7.1.4-1)

For spherical surfaces:

Ps = 40 2

3

2

2

1

1

1 s

y

E

F

D

DD

(14.7.1.4-2)

where:

D1 = the diameter of the rocker or roller surface (mm), and

D2 = the diameter of the mating surface (mm) taken as:

Positive if the curvatures have the same sign, and

Infinite if the mating surface is flat.

Fy = specified minimum yield strength of the weakest steel at the contact surface (MPa)

Es = Young’s modulus for steel (MPa)

W = width of the bearing (mm)

14.7.2. PTFE Sliding Surfaces

PTFE may be used in sliding surfaces of bridge bearings to accommodate translation or rotation. All PTFE surfaces other than guides shall satisfy the requirements specified herein. Curved PTFE surfaces shall also satisfy Article 14.7.3.

14.7.2.1. PTFE SURFACE

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The PTFE surface shall be made from pure virgin PTFE resin satisfying the requirements of ASTM D 1457 or equivalent Vietnam standard. It shall be fabricated as unfilled sheet, filled sheet, or fabric woven from PTFE and other fibers.

Unfilled sheets shall be made from PTFE resin alone. Filled sheets shall be made from PTFE resin uniformly blended with glass fibers, carbon fibers, or other chemically inert filler. The filler content shall not exceed 15 percent for glass fibers and 25 percent for carbon fibers.

Sheet PTFE may contain dimples to act as reservoirs for lubricant. Unlubricated PTFE may also contain dimples. Their diameter shall not exceed 8 mm at the surface of the PTFE, and their depth shall be not less than 2 mm and not more than half the thickness of the PTFE. The reservoirs shall be uniformly distributed over the surface area and shall cover more than 20 percent but less than 30 percent of the contact surface. Dimples should not be placed to intersect the edge of the contact area. Lubricant shall be silicone grease, which satisfies US Military Specification MIL-S-8660 or equivalent ASTM.

Woven fiber PTFE shall be made from pure PTFE fibers. Reinforced woven fiber PTFE shall be made by interweaving high-strength fibers, such as glass, with the PTFE in such a way that the reinforcing fibers do not appear on the sliding face of the finished fabric.

14.7.2.2. MATING SURFACE

The PTFE shall be used in conjunction with a mating surface. Flat mating surfaces shall be stainless steel, and curved mating surfaces shall be stainless steel or anodized aluminum. Flat surfaces shall be stainless steel, Type 304, conforming to ASTM A167/A 264 or Vietnam equivalent and shall be provided with a surface finish of 0.20 m RMS or better. Finishes on curved

1050


metallic surfaces shall not exceed 0.4 m RMS. The mating surface shall be large enough to cover the PTFE at all times.

14.7.2.3. MINIMUM THICKNESS

14.7.2.3.1. PTFE

For all applications, the thickness of the PTFE shall be at least 1.5 mm after compression. Recessed sheet PTFE shall be at least 4.5 mm thick when the maximum dimension of the PTFE is less than or equal to 600 mm, and 6.0 mm when the maximum dimension of the PTFE is greater than 600 mm. Woven fabric PTFE, which is mechanically interlocked over a metallic substrate, shall have a minimum thickness of 1.5 mm and a maximum thickness of 3.0 mm over the highest point of the substrate.

14.7.2.3.2. Stainless Steel Mating Surfaces

The thickness of the stainless steel mating surface shall be at least 1.50 mm when the maximum dimension of the surface is less than or equal to 300 mm and at least 3.0 mm when the maximum dimension is larger than 300 mm.

Backing plate requirements shall be taken as specified in Article 14.7.2.6.2.

14.7.2.4 .CONTACT PRESSURE

The contact stress between the PTFE and the mating surface

1051


shall be determined at the strength limit state using the nominal area.

1052


The average contact stress shall be computed by dividing the load by the projection of the contact area on a plane perpendicular to the direction of the load. The contact stress at the edge shall be determined by taking into account the maximum moment transferred by the bearing assuming a linear distribution of stress across the PTFE.

Stresses shall not exceed those given in Table 1. Permissible stresses for intermediate filler contents shall be obtained by linear interpolation within Table 1.

Table 14.7.2.4-1 - Maximum Contact Stress for PTFE at the Strength Limit State (MPa)

Material Average Contact Stress

Edge Contact Stress

Permanent Loads

All Loads

Permanent Loads

All Loads

Unconfined PTFE: - - - -

Unfilled Sheets 14 20 18 25

Filled Sheets with Maximum Filler Content

28 40 35 55

Confined Sheet PTFE 30 40 35 55

Woven PTFE Fiber over a 30 40 35 55

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Metallic Substrate

Reinforced Woven PTFE over a Metallic Substrate

35 50 40 65

14.7.2.5. COEFFICIENT OF FRICTION

The service limit design coefficient of friction of the PTFE sliding surface shall be taken as specified in Table 1. Intermediate values may be determined by interpolation. The coefficient of friction shall be determined by using the stress level associated with the applicable load combination specified in Table 3.4.1-1. Lesser values may be used if verified by tests.

Where friction is required to resist nonseismic loads, the design coefficient of friction under dynamic loading may be taken as not more than 10 percent of the values listed in Table 1 for the bearing stress and PTFE type indicated.

The coefficients of friction in Table 1 are based on a 0.20 m finish mating surface. Coefficients of friction for rougher surface finishes must be established by test results in accordance with the AASHTO LRFD Bridge Construction Specifications, Section 18.1.5.2

The contract documents shall require certification testing from the production lot of PTFE to ensure that the friction actually achieved in the bearing is appropriate for the bearing design.

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Table 14.7.2.5-1 - Design Coeffcients of Friction - Service Limit State

Pressure (MPa)

Coefficient of Friction

3.5 7 14 > 20

Type PTFE

Dimpled Lubricated 0.04 0.03 0.025 0.02

Unfilled or Dimpled Unlubricated

0.08 0.07 0.05 0.03

Filled 0.24 0.17 0.09 0.06

Woven 0.08 0.07 0.06 0.045

14.7.2.6. ATTACHMENT

14.7.2.6.1.PTFE

Sheet PTFE confined in a recess in a rigid metal backing plate for one-half its thickness may be bonded or unbonded.

Sheet PTFE that is not confined shall be bonded to a metal surface or an elastomeric layer with a Shore A durometer

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hardness of at least 90 by an approved method.

Woven PTFE on a metallic substrate shall be attached to the metallic substrate by mechanical interlocking that can resist a shear force no less than 0.10 times the applied compressive force.

14.7.2.6.2. Mating Surface

The mating surface for flat sliding surfaces shall be attached to a backing plate by welding in such a way that it remains flat and in full contact with its backing plate throughout its service life. The weld shall be detailed to form an effective moisture seal around the entire perimeter of the mating surface to prevent interface corrosion. The attachment shall be capable of resisting the maximum friction force that can be developed by the bearing under service limit state load combinations. The welds for the attachment shall be clear of the contact and sliding area of the PTFE surface.

14.7.3. Bearing with Curved Sliding Surfaces

14.7.3.1. GENERAL

Bearings with curved sliding surfaces shall consist of two metal parts with matching curved surfaces and a low friction sliding interface. The curved surface may be either cylindrical or spherical. The material properties, characteristics, and friction properties of the sliding in Article 14.7.2 and 14.7.7.

The two surfaces of a sliding interface shall have equal nominal radii.

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14.7.3.2 . BEARING RESISTANCE

The radius of the curved surface shall be large enough to ensure that the maximum average bearing stress, SS, on the horizontal projected area of the bearing at the strength limit state shall satisfy the average stress specified in Article 14.7.2.4 or 14.7.7.3.

The factored resistance shall be taken as:

For cylindrical bearings:

Pr = DW (14.7.3.2-1)

For spherical bearings:

Pr = (14.7.3.2-2)

where:

Pr = factored compressive resistance (N)

D = diameter of the projection of the loaded surface of the bearing in the horizontal plane (mm)

= maximum average contact stress at the strength limit state permitted on PTFE by Table

14.7.2.4-1 or on bronze by Table 14.7.7.3-1 (MPa)

W = length of cylinder (mm)

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= resistance factor taken as 1.0

14.7.3.3. RESISTANCE TO LATERAL LOAD

Where bearings are required to resist horizontal loads at the strength limit state or extreme event limit state, an external restraint system shall be provided or:

For a cylindrical sliding surface, the horizontal load shall satisfy:

Hu (14.7.3.3-1)

For a spherical surface, the horizontal load shall satisfy:

Hu (14.7.3.3-2)

in which:

(14.7.3.3-3)

and

where:

Hu = factored horizontal load (N)

L = projected length of the sliding surface

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perpendicular to the rotation axis (mm)

PD = service compressive load due to permanent loads (N)

R = radius of the curved sliding surface (mm)

W = length of the cylindrical surface (mm)

= angle between the vertical and resultant applied load (RAD)

= design rotation angle at strength limit state (RAD)

= maximum average contact stress at the strength limit state permitted on PTFE

by Table 14.7.2.4-1 or on bronze by Table 14.7.7.3-1 (KSI)

= subtended semiangle of the curved surface (RAD)

14.7.4. Pot Bearings

14.7.4.1. GENERAL

Where pot bearings are provided with a PTFE slider to provide for both rotation and horizontal movement, such sliding surfaces and any guide systems shall be designed in accordance with the provisions of Articles 14.7.2 and 14.7.9.

The rotational elements of the pot bearing shall consist of at least a pot, a piston, an elastomeric disc, and sealing rings.

For the purpose of establishing the forces and deformations imposed on a pot bearing, the axis of rotation shall be taken as

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lying in the horizontal plane at midheight of the elastomeric disc.

14.7.4.2. MATERIALS

The elastomeric disc shall be made from a compound based on virgin natural rubber or virgin neoprene conforming to AASHTO M251 (ASTM D4014). The nominal hardness shall lie between 50 and 60 on the Shore A scale.

The pot and piston shall be made from structural steel conforming to AASHTO M 270M (ASTM A 709M); Grades 250, 345, or 345W; or from stainless steel conforming to ASTM A 240M. The finish of surfaces in contact with the elastomeric pad shall be smoother than 1.5 m. The yield strength and hardness of the piston shall not exceed that of the pot.

Brass sealing rings satisfying Articles 14.7.4.5.2 and 14.7.4.5.3 shall conform to ASTM B 36M (half hard) for rings of rectangular cross-section, and Federal Specification QQB626, Composition 2, for rings of circular cross-section.

14.7.4.3. GEOMETRIC REQUIREMENTS

The depth of the elastomeric disc, hr, shall satisfy:

hr (14.7.4.3-1)

where:

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Dp = internal diameter of pot (mm)

= design rotation specified in Article 14.4.2 (RAD)

The dimensions of the elements of a pot bearing shall satisfy the following requirements under the least favorable combination of factored displacements and rotations:

The pot shall be deep enough to permit the seal and piston rim to remain in full contact with the vertical face of the pot wall, and

Contact or binding between metal components shall not prevent further displacement or rotation.

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14.7.4.4. ELASTOMERIC DISC

The average stress on the elastomer at the service limit state should not exceed 25 MPa.To facilitate rotation, the top and bottom surfaces of the elastomer shall be treated with a lubricant that is not detrimental to the elastomer. Alternatively, thin PTFE discs may be used on the top and bottom of the elastomer.

14.7.4.5. SEALING RINGS

14.7.4.5.1. General

A seal shall be used between the pot and the piston. At the service limit state seals shall be adequate to prevent escape of elastomer under compressive load and simultaneously applied cyclic rotations. At the strength limit state, seals shall also be adequate to prevent escape of elastomer under compressive load and simultaneously applied static rotation.

Brass rings satisfying the requirements of either Articles 14.7.4.5.2 or 14.7.4.5.3 may be used without testing to satisfy the above requirements. The Engineer may approve other sealing systems on the basis of experimental evidence.

14.7.4.5.2. Rings with Rectangular Cross-Sections

Three rectangular rings shall be used. Each ring shall be circular in plan but shall be cut at one point around its circumference. The faces of the cut shall be on a plane at 45o to the vertical and to the tangent of the circumference. The rings shall be

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oriented so that the cuts on each of the three rings are equally spaced around the circumference of the pot.

The width of each ring shall not be less than either 0.02 Dp or 6.0 mm and shall not exceed 19 mm. The depth of each shall not be less than 0.2 times its width.

14.7.4.5.3. Rings with Circular Cross-Sections

One circular closed ring shall be used with an outside diameter of Dp. It shall have a cross-sectional diameter not less than either 0.0175 Dp or 8 mm.

14.7.4.6. POT

The pot shall consist at least of a wall and base. All elements of the pot shall be designed to act as a single structural unit.

The minimum thickness of a base bearing directly against concrete or grout shall satisfy:

tbase 0.06 Dp and (14.7.4.6-1)

tbase 19 mm (14.7.4.6-2)

The thickness of a base bearing directly on steel girders or load distribution plates shall satisfy:

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tbase 0.04 Dp and (14.7.4.6-3)

tbase 12.5 mm (14.7.4.6-4)

In lieu of a more precise analysis, the factored bearing resistance of an unguided sliding pot bearing wall may be taken as:

Pr = 2 (14.7.4.6-5)

in which:

tw 20 mm (14.7.4.6-6)

where:

Pr = factored resistance of pot wall (N)

tw = pot wall thickness (mm)

Fy = yield strength of the steel (MPa)

hp = depth of the pot (mm)

= resistance factor taken as 0.90

The wall thickness of guided or fixed pots shall be determined for applicable strength and extreme event load combinations specified in Table 3.4.1-1 using a rational analysis.

14.7.4.7. PISTON

The piston shall have the same plan shape as the inside of the pot. Its thickness shall be adequate to resist the loads imposed on it, but shall not be less than 6 percent of the inside diameter

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of the pot, Dp, except at the rim.

The perimeter of the piston shall have a contact rim through which horizontal loads may be transmitted. In circular pots, its surface may be either cylindrical or spherical. The body of the piston above the rim shall be set back or tapered to prevent binding. The height, w, of the piston rim shall be large enough to transmit the factored horizontal forces between the pot and the piston.

Pot bearings subjected to lateral loads shall be proportioned to satisfy:

tw (14.7.4.7-1)

Pot bearings that transfer load through the piston shall satisfy:

w (14.7.4.7-2)

w 3.2 mm (14.7.4.7-3)

where:

Hs = horizontal service load on the bearing (N)

= maximum service rotation due to total load (RAD)

Fy = yield strength of steel (MPa)

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w = height of piston rim (mm)

tw = pot wall thickness (mm)

The diameter of the piston rim shall be the inside diameter of the pot less a clearance, c. The clearance, c, shall be as small as possible in order to prevent escape of the elastomer but not less than 0.5 mm. If the surface of the piston rim is cylindrical, the clearance shall satisfy:

c (14.7.4.7-4)

where:


W = height of piston rim (mm)

= design rotation specified in Article 14.4.2 (RAD)

14.7.5. Steel-Reinforced Elastomeric Bearings - Method B

14.7.5.1. GENERAL

Steel-reinforced elastomeric bearings may be designed using either of two methods commonly referred to as Method A and Method B. Where the provisions of this article are used, the component shall be taken to meet the requirements of Method B. Where the provisions of Article 14.7.6 are used, the

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component shall be taken to meet the requirements of Method A.

Steel-reinforced elastomenc bearings shall consist of alternate layers of steel reinforcement and elastomer bonded together. In addition to any internal reinforcement, bearings may have external steel load plates bonded to either or both the upper or lower elastomer layers.

Tapered elastomer layers shall not be used. All internal layers of elastomer shall be of the same thickness. The top and bottom cover layers shall be no thicker than 70 percent of the internal layers.

The shape factor of a layer of an elastomeric bearing, S i, shall be taken as the plan area of the layer divided by the area of perimeter free to bulge. For rectangular bearings without holes, the shape factor of a layer may be taken as:

Si = (14.7.5.1-1)

where:

L = length of a rectangular elastomenc bearing (parallel to longitudinal bridge axis) (mm)

W = width of the bearing in the transverse direction (mm)

hri = thickness of ith elastomeric layer in elastomeric bearing (mm)

For circular bearings without holes, the shape factor of a layer may be taken as:

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Si = (14.7.5.1-2)

where:

D = diameter of the projection of the loaded surface of the bearing in the horizontal plane

(mm)

14.7.5.2 . MATERIAL PROPERTIES

The elastomer shall have a shear modulus between 0.60 and 1.3 MPa and a nominal hardness between 50 and 60 on the Shore A scale. It shall conform to the requirements of Section 818 of the Construction Specification.

The shear modulus of the elastomer at 230C shall be used as the basis for design. If the elastomer is specified explicitly by its shear modulus, that value shall be used in design, and the other properties shall be obtained from Table 1. If the material is specified by its hardness, the shear modulus shall be taken as the least favorable value from the range for that hardness given in Table 1. Intermediate values may be obtained by interpolation.

Table 14.7.5.2-1 - Shear Modulus, G

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Hardness (Shore A)

50 60 70

Shear Modulus @ 23 oC (MPa)

0.66 – 0.90 0.90 – 1.38 1.38 – 2.07

Creep deflection @ 25 years divided by instantaneous deflection

0.25 0.35 0.45

14.7.5.3. DESIGN REQUIREMENTS

14.7.5.3.1. Scope

Bearings designed by the provisions herein shall be tested in accordance with the requirements for steel-reinforced elastomeric bearings as specified in Section 818 of the Construction Specification.

14.7.5.3.2 . Compressive Stress

In any elastomeric bearing layer, the average compressive stress at the service limit state shall satisfy:

For bearings subject to shear deformation:

(14.7.5.3.2-1)

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(14.7.5.3.2-2)

For bearings fixed against shear deformation:

(14.7.5.3.2-3)

(14.7.5.3.2-4)

where:

= service average compressive stress due to the total load (MPa)

= service average compressive stress due to live load (MPa)

G = shear modulus of elastomer (MPa)

S = shape factor of the thickest layer of the bearing

14.7.5.3.3. Compressive Deflection

Deflections of elastomeric bearings due to total load and to live load alone shall be considered separately.

Instantaneous deflection shall be taken as:

(14.7.5.3.3-1)

where:

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= instantaneous compressive strain in ith elastomer layer of a laminated bearing

hri = thickness of ith elastomeric layer in a laminated bearing (mm)

Values for shall be determined from test results or by analysis when considering long-term deflections. The effects of creep of the elastomer shall be added to the instantaneous deflection. Creep effects should be determined from information relevant to the elastomeric compound used. In the absence of material-specific data, the values given in Article 14.7.5.2 may be used.

14.7.5.3.4. Shear Deformation

The horizontal movement of the bridge superstructure, o, shall be taken as the extreme displacement caused by creep, shrinkage, posttensioning, combined with thermal effects computed in accordance with Article 3.12.2.

The maximum shear deformation of the bearing, at the service limit state, s, shall be taken as o modified to account for the substructure stiffness and construction procedures. If a low friction sliding surface is installed, s need not be taken to be larger than the deformation corresponding to first slip.

The bearing shall satisfy:

hrt = 2 s (14.7.5.3.4-1)

where:

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hrt = total elastomer thickness (mm)

S = maximum shear deformation of the elastomer at the service limit state (mm)

14.7.5.3.5. Combined Compression and Rotation

The provisions of this section shall apply at the service limit state. Rotations shall be taken as the maximum sum of the effects of initial lack of parallelism and subsequent girder end rotation due to imposed loads and movements.

Bearings shall be designed so that uplift does not occur under any combination of loads and corresponding rotations.

Rectangular bearings may be taken to satisfy uplift requirements if they satisfy:

> 1.0 G S (14.7.5.3.5-1)

Rectangular bearings subjected to shear deformation shall also satisfy:

< 1.875 G S (14.7.5.3.5-2)

Rectangular bearings fixed against shear deformation shall also

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satisfy:

< 2.25 G S (14.7.5.3.5-3)

where:

n = number of interior layers of elastomerhri = height of the ith elastomer layer (mm)

= stress in elastomer (MPa)

B = length of pad if rotation is about its transverse axis or width of pad if rotation is about

its longitudinal axis (mm)

= maximum service rotation due (RAD)

Circular bearings may be taken to satisfy uplift requirements if they satisfy:

> 0.75 G S (14.7.5.3.5-4)

Circular bearings subjected to shear deformation shall also satisfy:

< 2.5 G S (14.7.5.3.5-5)

Circular bearings fixed against shear deformation shall also satisfy:

< 3.0 G S (14.7.5.3.5-6)

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where:

= maximum service rotation due to the total load (RAD)

D = diameter of pad (mm)

14.7.5.3.6. Stability of Elastomeric Bearings

Bearings shall be investigated for instability at the service limit state load combinations specified in Table 3.4.1-1.

Bearings satisfying Equation 1 shall be considered stable, and no further investigation of stability is required.

2A B (14.7.5.3.6-1)

for which:

A = (14.7.5.3.6-2)

B = (14.7.5.3.6-3)

where:

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L = length of a rectangular elastomeric bearing (parallel to longitudinal bridge axis) (mm)

W = width of the bearing in the transverse direction (mm)

where:

For a rectangular bearing where L is greater than W, stability shall be investigated by interchanging L and W in Equations 2 and 3.

For circular bearings, stability may be investigated by using the equations for a square bearing with W = L = 0.8 D.

For rectangular bearings, the service average compressive stress due to the total load, , shall satisfy:

If the bridge deck is free to translate horizontally:

(14.7.5.3.6-4)

If the bridge deck is fixed against horizontal translation:

(14.7.5.3.6-5)

14.7.5.3.7. Reinforcement

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The thickness of the steel reinforcement, hs, shall satisfy:

At the service limit state:

hs 1.6 mm (14.7.5.3.7-1)

At the fatigue limit state:

hs 1.6 mm

(14.7.5.3.7-2)where:

= constant amplitude fatigue threshold for Category A as specified in Article 6.6 (MPa)

h max = thickness of thickest elastomeric layer in elastomeric bearing (mm)

= service average compressive stress due to live load (MPa)

= service average compressive stress due to total load (MPa)

Fy = yield strength of steel reinforcement (MPa)

If holes exist in the reinforcement, the minimum thickness shall be increased by a factor equal to twice the gross width divided by the net width.

14.7.5.3.8. Seismic Provisions

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Elastomeric expansion bearings shall be provided with adequate seismic resistant anchorage to resist the horizontal forces in excess of those accommodated by shear in the pad. The sole plate and the base plate shall be made wider to accommodate the anchor bolts. Inserts through the elastomer should not be allowed, unless approved by the Engineer. The anchor bolts shall be designed for the combined effect of bending and shear for seismic loads as specified in Article 14.6.5.3. Elastomeric fixed bearings shall be provided with horizontal restraint adequate for the full horizontal load.

14.7.6. Elastomeric Pads and Steel Reinforced Elastomeric Bearings - Method A

14.7.6.1. GENERAL

The provisions of this article apply to the design of:

Plain elastomeric pads, PEP;

Pads reinforced with discrete layers of fiberglass, FGP; and

Pads reinforced with closely spaced layers of cottonduck, CDP, and steel-reinforced elastomeric bearings.

Layer thicknesses in FGP may be different from one another. For steel-reinforced elastomeric bearings designed in accordance with the provisions of this section, internal layers shall be of the same thickness, and cover layers shall be no more than 70 percent of the thickness of internal layers.

The shape factor for pads and steel reinforced elastomeric bearings covered by this article is determined as specified in Article 14.7.5.1.

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14.7.6.2 . MATERIAL PROPERTIES

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The materials shall satisfy the requirements of Article 14.7.5.2, except that the shear modulus shall be between 0.60 MPa and 1.75 MPa, and the nominal hardness shall be between 50 and 70 on the Shore “A” scale and shall conform to the requirements of Section 818 of the Construction Specification. This exception shall not apply to steel-reinforced elastomeric bearings designed in accordance with the provisions of this section.

The shear force on the structure induced by deformation of the elastomer shall be based on a G value not less than that of the elastomer at 230C. Effects of relaxation shall be ignored.

14.7.6.3 . DESIGN REQUIREMENTS

14.7.6.3.1. Scope

Steel-reinforced elastomeric bearings may be designed in accordance with this article, in which case they qualify for the test requirements appropriate for elastomeric pads.

The provisions for FGP apply only to pads where the fiberglass is placed in double layers 3.0 mm apart.

The physical properties of neoprene and natural rubber used in these bearings shall conform to the following ASTM or AASHTO requirements, with modifications as noted:

ASTM AASHTO

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Compound Requirement Requirement

Neoprene D4014 AASHTO M251

Natural Rubber D4014 AASHTO M251

Modifications:

The Shore A durometer hardness shall be 50± 10 points, and

Samples for compression set tests shall be prepared using a Type 2 die.

14.7.6.3.2. Compressive Stress

At the service limit state, the average compressive stress, , in any layer shall satisfy:

For PEP:

(14.7.6.3.2-1)

For FGP:

1.00 G S 5.5 MPa (14.7.6.3.2-2)

For CDP:

10.5 MPa (14.7.6.3.2-3)

In FGP, the value of S used shall be that for the greatest distance between the midpoint of double reinforcement layers

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at the top and bottom of the elastomer layer.

For steel-reinforced elastomeric bearings designed in accordance with the provisions of this article:

7 MPa and 1.0 GS (14.7.6.3.2-4)

where the value of S used shall be that for the thickest layer of the bearing.

These stress limits may be increased by 10 percent where shear deformation is prevented.

14.7.6.3.3. Compressive Deflection

The provisions of Article 14.7.5.3.3 shall apply.

14.7.6.3.3. Shear

The horizontal bridge movement shall be computed in accordance with Article 14.4. The maximum shear deformation of the pad, , shall be taken as the horizontal bridge movement, reduced to account for the pier flexibility and modified for construction procedures. If a low friction sliding surface is used, need not be taken to be larger than the deformation corresponding to first slip.

The provisions of Article 14.7.5.3.4 shall apply, except that the pad shall be designed as follows:

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For PEP, FGP and steel-reinforced elastomeric bearings:

hrt 2 (14.7.6.3.4-1)

For CDP:

hrt 10 (14.7.6.3.4-2)

14.7.6.3.5 Rotation

The provisions of this section shall apply at the service limit state. Rotations shall be taken as the maximum sum of the effects of initial lack of parallelism and subsequent girder end rotation due to imposed loads and movements.

Rectangular pads shall satisfy:

(14.7.6.3.5-1)

(14.7.6.3.5-2)

Circular pads shall satisfy:

(14.7.6.3.5-3)

where:

= service average compressive stress due to total load (MPa)


S = shape factor of thickest layer of an elastomeric bearing

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L = length of a rectangular elastomeric bearing (parallel to longitudinal bridge axis) (mm)

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hrt = total elastomer thickness in an elastomeric bearing (mm)W = width of the bearing in the transverse direction (mm)D = diameter of pad (mm)

= rotation about any axis of the pad (RAD)

= service rotation due to total load about transverse axis (RAD)

= service rotation due to total load about longitudinal axis (RAD)

14.7.6.3.6. Stability

To ensure stability, the total thickness of the pad shall not exceed the least of L/3, W/3, or D/4.

14.7.6.3.7. Reinforcement

The reinforcement in FGP shall be fiberglass with a strength in each plan direction of at least 15.2 hri in N/mm. For the purpose of this article, if the layers of elastomer are of different thicknesses, hri shall be taken as the mean thickness of the two layers of the elastomer bonded to the same reinforcement. If the fiberglassreinforcement contains holes, its strength shall be increased over the minimum value specified herein by twice the gross width divided by net width.

Reinforcement for steel-reinforced elastomeric bearings designed in accordance with the provisions of this article shall conform to the requirements of Article 14.7.5.3.7.

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14.7.6.4. ANCHORAGE

If the factored shear force sustained by the deformed pad at the strength limit state exceeds one-fifth of the minimum vertical force, Psd, due to permanent loads, the pad shall be secured against horizontal movement.

14.7.7. Bronze or Copper Alloy Sliding Surfaces

14.7.7.1. MATERIALS

Bronze or copper alloy may be used for:

Flat sliding surfaces to accommodate translational movements,

Curved sliding surfaces to accommodate translation and limited rotation, and

Pins or cylinders for shaft bushings of rocker bearings or other bearings with large rotations.

Bronze sliding surfaces or castings shall conform to AASHTO M 107 (ASTM B 22) and shall be made of Alloy C90500, C91100, or C 86300, unless otherwise specified. The mating surface shall be structural steel, which has a Brinell hardness value at least 100 points greater than that of the bronze.

Bronze or copper alloy sliding expansion bearings shall be evaluated for shear capacity and stability under lateral loads.

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The mating surface shall be made of steel and be machined to match the geometry of the bronze surface so as to provide uniform bearing and contact.

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14.7.7.2 . COEFFICIENT OF FRICTION

The coefficient of friction may be determined by testing. In lieu of such test data, the design coefficient of friction may be taken as 0.1 for self-lubricating bronze components and 0.4 for other types.

14.7.7.3. LIMIT ON LOAD

The nominal bearing stress due to combined dead and live load at the strength limit state shall not exceed the values given in Table 1.

Table 14.7.7.3-1 - Bearing Stress at the Strength Limit State

AASHTO M 107 (ASTM B 22) BRONZE ALLOY

BEARING STRESS (MPa)

C90500 – Type 1 21

C91100 – Type 2 21

C86300 – Type 3 83

14.7.7.4. CLEARANCES AND MATING SURFACES

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The mating surface shall be steel that is accurately machined to match the geometry of the bronze surface and to provide uniform bearing and contact.

14.7.8. Disc Bearings

14.7.8.1. GENERAL

The dimensions of the elements of a disc bearing shall be such that hard contact between metal components, which prevents further displacement or rotation, will not occur under the least favorable combination of design displacements and rotations at the strength limit state.

The disc bearing shall be designed for the design rotation, , specified in Article 14.4.2.

For the purpose of establishing the forces and deformations imposed on a disc bearing, the axis of rotation may be taken as lying in the horizontal plane at midheight of the disc. The urethane disc shall be held in place by a positive location device.

Limiting rings may be used to partially confine the elastomer against lateral expansion. They may consist of steel rings welded to the upper and lower plates or a circular recess in each of those plates.

If a limiting ring is used, the depth of the ring should be at least 0.03Dd.

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14.7.8.2. MATERIALS

The elastomeric disc shall be made from a compound based on polyether urethane, using only virgin materials. The hardness shall be between 45 and 65 on the Shore D scale.

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The metal components of the bearing shall be made from structural steel conforming to AASHTO M 270M or M 183 (ASTM A 709M), Grade 250, 345, or 345W or from stainless steel conforming to ASTM A 240M.

14.7.8.3. ELASTOMERIC DISC

The elastomeric disc shall be held in location by a positive locator device.

At the service limit state, the disc shall be designed so that:

Its instantaneous deflection under total load does not exceed 10 percent of the thickness of the unstressed disc, and the additional deflection due to creep does not exceed 8 percent of the thickness of the unstressed disc;

The components of the bearing do not lift off each other at any location; and

The average compressive stress on the disc does not exceed 35 MPa. If the outer surface of the disc is not vertical, the stress shall be computed using the smallest plan area of the disc.

If a PTFE slider is used, the stresses on the PTFE slider shall not exceed 75 percent of the values for average and edge stresses given in Article 14.7.2.4 for the strength limit state. The effect of moments induced by the urethane disc shall be included in the stress analysis.

14.7.8.4. SHEAR RESISTING MECHANISM

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In fixed and guided bearings, a shear-resisting mechanism shall be provided to transmit horizontal forces between the upper and lower steel plates. It shall be capable of resisting a horizontal force in any direction equal to the larger of the design shear force or 10 percent of the design vertical load.

The horizontal design clearance between the upper and lower components of the shear-resisting mechanism shall not exceed the value for guide bars given in Article 14.7.9.

14.7.8.5. STEEL PLATES

The provisions of Sections 3, 4, and 6 of this Specification shall apply as appropriate.

The thickness of each of the upper and lower steel plates shall not be less than 0.045 Dd, if it is in direct contact with a steel girder or distribution plate, or 0.06 Dd if it bears directly on grout or concrete.

14.7.9. Guides and Restraints

14.7.9.1. GENERAL

Guides may be used to prevent movement in one direction. Restraints may be used to permit only limited movement in one or more directions. Guides and restraints shall have a low-friction material at their sliding contact surfaces.

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14.7.9.2 . DESIGN LOADS

Guides or restraints shall be designed using the strength limit state load combinations specified in Table 3.4.1-1 for the larger of either:

The factored horizontal design force, or

10 percent of the total factored vertical force acting on all the bearings at the bent divided by the number of guided bearings at the bent.

Guides and restraints shall be designed for applicable seismic or collision forces using the extreme event limit state load combination of Table 3.4.1-1.

14.7.9.3 . MATERIALS

For steel bearings, the guide or restraint shall be made from steel conforming to AASHTO M 270M (ASTM A 709M), Grades 250, 345, or 345W or stainless steel conforming to ASTM A 240M. For aluminum bearings, the guide may also be aluminum.

The low-friction interface material shall be approved by the Engineer.

14.7.9.4.GEOMETRIC REQUIREMENTS

Guides shall be parallel, long enough to accommodate the full

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design displacement of the bearing in the sliding direction, and shall permit a minimum of 0.8 mm and a maximum of 1.6 mm free slip in the restrained direction. Guides shall be designed to avoid binding under all design loads and displacements, including rotation.

14.7.9.5 . DESIGN BASIS

14.7.9.5.1. Load Location

The horizontal force acting on the guide or restraint shall be assumed to act at the centroid of the low-friction interface material. design of the connection between the guide or restraint and the body of the bearing system shall consider both shear and the overturning moments so caused.

The design and detailing of bearing components resisting lateral loads, including seismic loads determined as specified in Article 14.6.3.1, shall provide adequate strength and ductility. Guide bars and keeper rings or nuts at the ends of pins and similar devices shall either be designed to resist all imposed loads or an alternative load path shall be provided that engages before the relative movement of the substructure and superstructure is excessive.

14.7.9.5.2. Contact Stress

The contact stress on the low-friction material shall not exceed that recommended by the manufacturer. For PTFE, the stresses at strength limit state shall not exceed those specified in Table 14.7.2.4-1 under sustained loading or 1.25 times those stresses for short-term loading.

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14.7.9.6. ATTACHMENT OF LOW-FRICTION MATERIAL

The low-friction material shall be attached by at least any two of the following three methods:

Mechanical fastening

Bonding

Mechanical interlocking with a metal substrate

14.7.10. Other Bearing Systems

Bearing systems made from components not specified in Articles 14.7.1 through 14.7.9 may also be used, subject to the approval of the Engineer. Such bearings shall be adequate to resist the forces and deformations imposed on them at the service, strength, and extreme event limit states without material distress and without inducing deformations detrimental to their proper functioning.

The dimensions of the bearing shall be chosen to provide for adequate movements at all times. Materials shall have sufficient strength, stiffness, and resistance to creep and decay to ensure the proper functioning of the bearing throughout the design life of the bridge.

The Engineer shall determine the tests that the bearing shall satisfy. The tests shall be designed to demonstrate any potential weakness in the system under individual compressive, shear, or rotational loading or combinations thereof. Testing under sustained and cyclic loading shall be required.

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14.8. LOAD PLATES AND ANCHORAGE FOR BEARINGS

14.8.1. Plates for Load Distribution

The bearing, together with any additional plates, shall be designed so that:

The combined system is stiff enough to prevent distortions of the bearing that would impair its proper functioning;

The stresses imposed on the supporting structure satisfy the limits specified by the Engineer and Sections 5 or 6; and

The bearing can be replaced within the jacking height limits specified by the Engineer without damage to the bearing, distribution plates, or supporting structure. If no limit is given, a height of 10mm shall be used.

Resistance of steel components shall be determined in accordance with Section 6.

In lieu of a more refined analysis, the load from a bearing fully supported by a grout bed may be assumed to distribute at a slope of 1.5:1, horizontal to vertical, from the edge of the smallest element of the bearing that resists the compressive load.

The use and design of bearing stiffeners on steel girders shall comply with Section 6.

Sole plate and base plate connections shall be adequate to resist lateral loads, including seismic loads, determined as

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specified in Article 14.6.5.3. Sole plates shall be extended to allow for anchor bolt inserts, when required.

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14.8.2. Tapered Plates

If, under full unfactored permanent load at the mean annual temperature for the bridge site, the inclination of the underside of the girder to the horizontal exceeds 0.01 RAD, a tapered plate shall be used in order to provide a level surface.

14.8.3. Anchorage and Anchor Bolts

14.8.3.1.GENERAL

All load distribution plates and bearings with external steel plates shall be positively secured to their supports by bolting or welding.

All girders shall be positively secured to supporting bearings by a connection that can resist the horizontal forces that may be imposed on it. Separation of bearing components shall not be permitted. Connections shall resist the least favorable combination of loads at the strength limit state and shall be installed wherever deemed necessary to prevent separation.

Trusses, girders, and rolled beams shall be securely anchored to the substructure. Where possible, anchor bolts should be cast in substructure concrete, otherwise anchor bolts may be grouted in place. Anchor bolts may be swedged or threaded to secure a satisfactory grip upon the material used to embed them in the holes.

The factored resistance of the anchor bolts shall be greater than the factored force effects due to Strength I load

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combination and to all applicable extreme event load combinations.

The tensile resistance of anchor bolts shall be determined as specified in Article 6.13.2.10.2.

The shear resistance of anchor bolts and dowels shall be determined as specified in Article 6.13.2.7.

The resistance of anchor bolts in combined tension and shear shall be determined as specified in Article 6. 13.2.11.

The bearing resistance of the concrete shall be taken as specified in Article 5.7.5. The modification factor, m, shall be based on a nonuniformly distributed bearing stress.

14.8.3.2. SEISMIC DESIGN AND DETAILING REQUIREMENTS

Anchor bolts used to resist seismic loads shall be designed for ductile behavior. Sufficient reinforcement shall be provided around the anchor bolts to develop the horizontal forces and anchor them into the mass of the substructure unit. Potential concrete crack surfaces next to the bearing anchorage shall be identified and their shear friction capacity evaluated.

14.9. CORROSION PROTECTION

All exposed steel parts of bearings not made from stainless steel shall be protected against corrosion by zinc metalization, hot-dip galvanizing, or a paint system approved by the

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Engineer. A combination of zinc metalization or hot-dip galvanizing and a paint system may be used.

TABLE OF CONTENTS

Section 1. INTRODUCTION.......................................... 1

1.1. SCOPE OF THE SPECIFICATION................................. 1

1.2. DEFINITIONS........................................................... 2

1.3. DESIGN PHILOSOPHY............................................ 3

Section 2. GENERAL DESIGN AND LOCATION FEATURES.....................................................................

7

2.1. SCOPE...................................................................... 7

2.2. DEFINITIONS............................................................ 7

2.3. LOCATION FEATURES............................................... 9

2.4. FOUNDATION INVESTIGATION.................................. 14

2.5. DESIGN OBJECTIVES................................................. 14

2.6. HYDROLOGY AND HYDRAULICS............................... 20

Section 3. LOADS AND LOAD FACTORS.................... 27

3.1. SCOPE...................................................................... 27

3.2. DEFINITIONS............................................................ 27

3.3. NOTATION................................................................ 29

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3.4. LOAD FACTORS AND COMBINATIONS .................... 32

3.5. PERMANENT LOADS................................................. 36

3.6. LIVE LOADS.............................................................. 36

3.7. WATER LOADS: WA.................................................. 44

3.8. WIND LOAD: WL AND WS ........................................ 45

3.9. NOT USED................................................................ 49

3.10. EARTHQUAKE EFFECTS: EQ.................................... 49

3.11. EARTH PRESSURE: EH, ES, LS, and DD ................. 57

3.12. FORCE EFFECTS DUE TO SUPERIMPOSED DEFORMATIONS: TU, TG, SH, CR, SE....................

69

3.13. FRICTION FORCES: FR............................................ 72

3.14. VESSEL COLLISION: CV.......................................... 72

Section 4. STRUCTURAL ANALYSIS AND EVALUATION.................................................................

79

4.1. SCOPE..............................................................................................................................................................

79

4.2. DEFINITIONS.....................................................................................................................................................

79

4.3. NOTATION................................................................................................................................................................................................................................................

83

4.4. ACCEPTABLE METHODS OF STRUCTURAL ANALYSIS........................................................................................

85

4.5. MATHEMATICAL MODELING..............................................................................................................................

86

4.6. STATIC ANALYSIS.............................................................................................................................................

90

4.7. DYNAMIC ANALYSIS.................................................. 122

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........................................................................................

4.8. ANALYSIS BY PHYSICAL MODELS......................................................................................................................

127

Section 5. CONCRETE STRUCTURES.......................... 128

5.1. SCOPE..............................................................................................................................................................

128

5.2. DEFINITIONS.....................................................................................................................................................

128

5.3. NOTATION........................................................................................................................................................

132

5.4. MATERIAL PROPERTIES.....................................................................................................................................

138

5.5. LIMIT STATES....................................................................................................................................................

145

5.6. DESIGN CONSIDERATIONS...............................................................................................................................

149

5.7. DESIGN FOR FLEXURAL AND AXIAL FORCE EFFECTS........................................................................................

153

5.8. SHEAR AND TORSION.......................................................................................................................................

168

5.9. PRESTRESSING AND PARTIAL PRESTRESSING..................................................................................................

182

5.10. DETAILS OF REINFORCEMENT.......................................................................................................................

195

5.11. DEVELOPMENT AND SPLICES OF REINFORCEMENT........................................................................................

219

5.12. DURABILITY....................................................................................................................................................

230

5.13. SPECIFIC MEMBERS........................................................................................................................................

233

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5.14. PROVISIONS FOR STRUCTURE TYPES.............................................................................................................

246

Section 6. STEEL STRUCTURES.................................. 268

6.1. SCOPE..................................................................... .......................................................................................

268

6.2. DEFINITIONS ........................................................... ........................................................................................

268

6.3. NOTATION............................................................... ........................................................................................

272

6.4. MATERIALS.......................................................................................................................................................

279

6.5. LIMIT STATES........................................................... .......................................................................................

283

6.6. FATIGUE AND FRACTURE CONSIDERATIONS....................................................................................................

285

6.7. GENERAL DIMENSION AND DETAIL REQUIREMENTS .......................................................................................

300

6.8. TENSION MEMBERS..........................................................................................................................................

6.9. COMPRESSION MEMBERS.................................................................................................................................

6.10. I-SECTIONS IN FLEXURE.................................................................................................................................

6.11. BOX SECTIONS IN FLEXURE....................................

6.12. MISCELLANEOUS FLEXURAL MEMBERS..........................................................................................................

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6.13. CONNECTIONS AND SPLICES..........................................................................................................................

6.14. PROVISIONS FOR STRUCTURE TYPES.............................................................................................................

Section 9. DECKS AND DECK SYSTEMS....................

9.1. SCOPE..............................................................................................................................................................

9.2. DEFINITIONS.....................................................................................................................................................

9.3. NOTATION........................................................................................................................................................

9.4. GENERAL DESIGN REQUIREMENTS...................................................................................................................

9.5. LIMIT STATES....................................................................................................................................................

9.6. ANALYSIS..........................................................................................................................................................

9.7. CONCRETE DECK SLABS...................................................................................................................................

9.8. STEEL DECKS....................................................................................................................................................

Section 10. FOUNDATIONS.........................................

10.1. SCOPE................................................................... .......................................................................................

10.2. DEFINITIONS...................................................................................................................................................

10.3. NOTATION......................................................................................................................................................

10.4. DETERMINATION OF SOIL PROPERTIES...................

10.5. LIMIT STATES AND RESISTANCE FACTORS.............

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.......................................................................................

10.6. SPREAD FOOTINGS........................................................................................................................................

10.7. DRIVEN PILES................................................................................................................................................

10.8. DRILLED SHAFTS...........................................................................................................................................

Section 11. ABUTMENTS, PIERS AND WALLS..........

11.1. SCOPE............................................................................................................................................................

11.2. DEFINITIONS...................................................................................................................................................

11.3. NOTATION......................................................................................................................................................

11.4. SOIL PROPERTIES AND MATERIALS.................................................................................................................

11.5. LIMIT STATES AND RESISTANCE FACTORS....................................................................................................

11.6.ABUTMENTS AND CONVENTIONAL RETAINING WALLS.............................................................................

11.7. PIERS .....................................................................

11.8. ANCHORED WALLS................................................

11.9. MECHANICALLY STABILIZED EARTH WALLS............

11.10. PREFABRICATED MODULAR WALLS......................

Section 12. BURIED STRUCTURES AND TUNNEL LINERS...........................................................................

12.1. SCOPE....................................................................

12.2. DEFINITIONS...........................................................

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12.3. NOTATION..............................................................

12.4. SOIL AND MATERIAL PROPERTIES...........................

12.5. LIMIT STATES AND RESISTANCE FACTORS ............

12.6. GENERAL DESIGN FEATURES..................................

12.7. METAL PIPE, PIPE ARCH, AND ARCH STRUCTURES.

12.8. LONG-SPAN STRUCTURAL PLATE STRUCTURES......

12.9. STRUCTURAL PLATE BOX STRUCTURES.................

12. 10. REINFORCED CONCRETE PIPE.............................

12.11. REINFORCED CONCRETE CAST-IN-PLACE AND PRECAST BOX CULVERTS AND REINFORCED CAST-IN-PLACE ARCHES.....................................................

12.12. THERMOPLASTICPIPES

12.13. STEEL TUNNEL LINER PLATE ................................

12.14. PRECAST REINFORCED CONCRETE THREE-SIDED STRUCTURES ..................................................................

Section 13. RAILINGS

13.1. SCOPE....................................................................

13.2. DEFINITIONS...........................................................

13.3. NOTATION..............................................................

13.4. GENERAL................................................................

13.5. MATERIALS.............................................................

13.6. LIMIT STATES AND RESISTANCE FACTORS.............

13.7. TRAFFIC RAILING....................................................

13.8. PEDESTRIAN RAILINGS...........................................

13.9. BICYCLE RAILINGS.................................................

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13.10. COMBINATION RAILINGS......................................

13.11. CURBS AND SIDEWALKS.......................................

Section 14. JOINTS AND BEARINGS............................

14.1. SCOPE......................................................................

14.2. DEFINITIONS............................................................

14.3. NOTATION...............................................................

14.4. MOVEMENTS AND LOADS........................................

14.5. BRIDGE JOINTS........................................................

14.6. REQUIREMENTS FOR BEARINGS..............................

14.7. SPECIAL DESIGN PROVISIONS FOR BEARINGS.........

14.8. LOAD PLATES AND ANCHORAGE FOR BEARINGS.....

14.9. CORROSION PROTECTION ......................................

Note: Equations, figures and tables are denoted by their home article and an extension, for example 1.2.3.4.5-1, but when they are referenced in their home article they are identified only by extension. For example, in Article 1.2.3.4.5, Equation 1.2.3.4.5-2 would simply be called “Equation 2”. When this equation is referenced anywhere else other than its home article, it is identified by its whole nomenclature, in other words, “Equation 1.2.3.4.5-2”. The same convention applies to tables and figures.

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