EGCE 406: Bridge Design
Praveen Chompreda
Mahidol UniversityFirst Semester, 2010
Bearings & Substructures
1
Class Topics & Objectives Topics
Bridge Bearing
Bridge Substructures Loads on Substructure Abutment Piers
Objective Students can identify and describe
types of bridge bearings Students can describe the loads
involved in the design of substructures.
Students can describe pros and cons for each type of substructure
Parts of the topics discussed in this class can be found in:
Chapter 1-4
2
Load Transfer Loads on the bridge must find a way to the ground
Live Loadon Bridge
Deck Slab Superstructure
Girder Superstructure
Bearing
Substructure(Abutment/ Pier)
Foundation(Footing/ Pile)
Ground
Superstructure
Substructure
3
Components of Bridge
Abutment Abutment
Superstructure
Substructure
Roadway Deck
PierAbutment
Superstructure
Substructure
Roadway Deck
4Source: Nowak (2005)
BearingRole of Bearing
Forces and MovementsTypes
Selection of Bearing
5
Bearing Bearing is a structural device positioned
between bridge superstructure and substructure
Roles of Bearing: Transmit load from superstructure to
substructure Accommodate relative movements
between superstructure and substructure
Types: Fixed Bearing
Rotational movement only Expansion Bearing
Rotational movement Translational movement 6
Forces and Movements on Bearing Forces on Bearing
Vertical forces - from dead loads and live load Horizontal forces - from wind, earthquake
Movements on Bearing Horizontal translation caused by creep, shrinkage, and thermal
expansions. Rotations caused by traffic, construction tolerances, and uneven
settlement of foundations
If no movement is allowed, then the bearing must be able to resist the force due to the deformation
7
Types of Bearing Rocker Bearing Pin Bearing Roller Bearing Slider Bearing Elastomeric Bearing Curved Bearing
Pot Bearing Disk Bearing
8
Rocker/ Pin/ Roller Bearing
Mostly used for steel beams
Can carry large loads Requires high clearance Corrosion can be a
problem need regular inspections high maintenance cost
Source: Chen and Duan (2003)9
Rocker/ Pin/ Roller Bearing
Source: www.mageba.ch (2010)
10
Elastomeric Bearing
Made up of natural or synthetic rubber Very flexible in shear but very stiff against volumetric change Can accommodate both rotational and translational movements through
the deformation of pad Steel or fiberglass is typically used to reinforced the pad in alternate
layers to prevent it from “bulging” under high load, allowing it to resist higher loads
11
Source: Chen and Duan (2003)
Elastomeric Bearing with Slider
Steel slider with Teflon (PTFE – polytetrafluoroethylene) coated surfaces may be used in combination with elastomeric bearing to allow for more translations
12
Source: Chen and Duan (2003)
Elastomeric Bearing
Source: www.mageba.ch (2010)
13
Curved Bearing Curved Surface allows for
rotation Cylindrical Surface can
rotate only about 1 axis Spherical Surface can
rotate about any axes
Slider surface coated with Teflon must be used to allow for the translation
Can resist relatively large loads
14Source: Chen and Duan (2003)
Curved Bearing
Source: www.mageba.ch (2010)
15
Pot Bearing
Pot bearing consists of steel container (“Pot”) with elastomeric pad inside
Can resist much larger loads than conventional elastomeric bearing Rotation is accommodated by deformation of the elastomer Sliding surface is used to allow for translation
16
Source: Chen and Duan (2003)
Pot Bearing
Source: www.mageba.ch (2010)
17
Disk Bearing
Hard elastomeric disk is used with metal key inside Metal key is used to resist horizontal loads Rotation is accommodated by deformation of the elastomer Sliding surface is used to allow for translations
18
Source: Chen and Duan (2003)
Which type of bearing should I use? Consider the following factors when selecting a
bearing to use: Vertical and Horizontal Loads Translational and Rotational Movements
Available Clearance (footprint/ height) Environment (corrosion/ temperature range) Initial Cost Maintenance Cost
Availability Owner’s Preference
19
Bearing Capacity of Common Bearings
20Source: Chen and Duan (2003)
Substructures
21
Types of Substructures Abutment-Type Substructures
Abutment and Retaining Walls Anchored Walls Mechanically Stabilized Earth Walls Prefabricated Modular Walls
Pier-Type Substructures Concrete Pier Steel Pier Composite Steel & Concrete Pier
22
Types of Substructures
Abutment & Pier
PierAbutment
23
Loads on SubstructuresLoads from Superstructure
Loads on SubstructureLoad Combinations
24
Loads from Superstructure Vertical Loads from Superstructures
Dead Load of Structural and Nonstructural Components (DC) Dead Load of Wearing Surface (DW) Live Load (LL) and Impact (IM) Pedestrian Live Load (PL)
Horizontal Loads from Superstructures Wind Load on Structures (WS) Wind Load on Live Load (WL) Earthquake Load (EQ) Vehicular Braking Force (BR), Centrifugal Force (CE), and
Collision Force (CT) Creep (CR), Shrinkage (SH), Friction (FR), and Temperature
(TG/ TU)25
Loads on Substructures Vertical load acting on substructure
Dead Load of Structural and Nonstructural Components (DC) Vertical Pressure from Dead Load of Earth Fill (EV)
Horizontal loads acting on substructure Water Load and Stream Pressure (WA) Ice Load (IC) Wind Load on Structure (WS) Earthquake Load (EQ) Vehicular Collision Force (CT), Vessel Collision Force (CV) Horizontal Earth Pressure Load (EH) Earth Surcharge Load (ES) Live Load Surcharge (LS)
26
Wind Loads (WS, WL)
WS(on Substructure)
WS(on Superstructure)
WL
27
Vehicle Collision Forces (CT) Unless protected, abutments and piers located within a distance of 30.0
FT to the edge of roadway, or within a distance of 50.0 FT to the centerline of a railway track, shall be designed for an equivalent static force of 400 KIP, which is assumed to act in any direction in a horizontal plane, at a distance of 4.0 FT above ground.
CT need not be considered for structures which are protected by: An embankment A structurally independent, crashworthy groundmounted 54.0-IN high
barrier, located within 10.0 FT from the component being protected; Or a 42.0-IN high barrier located at more than 10.0 FT from the
component being protected
28
Load Combinations
29Source: AASHTO (2002)
Load Combinations
30Source: AASHTO (2002)
Design of Abutment and Retaining Substructures
Roles and TypesFailure Limit StatesLoads on Abutment
31
Roles and Types Roles of Abutment
Provide support for bridge superstructure at the bridge ends
Connect the bridge with the approach roadway
Retain the roadway material (soil & rock) from the bridge span
Types Abutment
Open End AbutmentClose End Abutment
Retaining StructuresGravity WallCantilever WallAnchored WallsMechanically
Stabilized Earth Walls Prefabricated
Modular Walls
32
Types of Abutment Open End
Abutment
Close End Abutment
33Source: Chen and Duan (2003)
Types of Abutment Open End Abutment
34Source: Nowak (2005)
Types of Abutment Close End Abutment
35Source: Nowak (2005)
Types of Abutment Open End Abutment
Has some slopes between abutment wall and roadway/ water channel below
Requires relatively larger space Requires longer bridge span Allow for some roadway
widening below bridge More economical
Close End Abutment Has no slopes between abutment
wall and roadway/ water channel below
Requires relatively smaller space (good for urban areas)
Requires shorter bridge span No allowance for future widening More expensive to construct
36Source: Chen and Duan (2003)
Types of Retaining Structures
37Source: Chen and Duan (2003)
Anchored Walls
Types of Retaining Structures
38Source: Chen and Duan (2003)
Types of Retaining Structures Mechanically Stabilized Earth Walls
39
Source: Nowak (2005)
Types of Retaining Structures
40
Source: Nowak (2005)
Types of Retaining Structures
41
Source: Chen and Duan (2003)
Failure Limit States Abutment structures must be checked for:
Global Stability Failure: Bearing Capacity (a) Overturning (b) Sliding Failure (c) Deep Seated Failure (d)
Local Strength Failures: Compression Failure Bending Moment Failure Shear Deflection Etc…
42
Source: Nowak (2005)
Strength Limit States (Global)
NT
(a) (b)
(d)(c)
43Source: Nowak (2005)
Loads on Abutment from Superstructure Vertical loads from superstructures
Dead Load of Structural and Nonstructural Components (DC) Dead Load of Wearing Surface (DW) Live Load (LL) and Impact (IM) Pedestrian Live Load (PL)
Horizontal loads from superstructures Wind Load on Structures (WS) Wind Load on Live Load (WL) Earthquake Load (EQ) Vehicular Braking Force (BR), Centrifugal Force (CE), and
Collision Force (CT) Creep (CR), Shrinkage (SH), Friction (FR), and Temperature
(TG/ TU)44
Loads on Abutment Itself Vertical loads acting on substructure
Dead Load of Structural and Nonstructural Components (DC) Vertical Pressure from Dead Load of Earth Fill (EV)
Horizontal loads acting on substructure Water Load and Stream Pressure (WA) Ice Load (IC) Earthquake Load (EQ) Vehicular Collision Force (CT), Vessel Collision Force (CV) Horizontal Earth Pressure Load (EH) Earth Surcharge Load (ES) Live Load Surcharge (LS)
45
Loads on Abutment
46
Source: Chen and Duan (2003)
Earth Pressure (EH, ES, LS and DD) Earth pressure is a function of the:
Type and unit weight of earth Water content Soil creep characteristics Degree of compaction Location of groundwater table Earth-structure interaction Amount of surcharge Earthquake effects
47
Earth Pressure (EH) Basic earth pressure, p
kh = coefficient of lateral earth pressure At-rest pressure coefficient, Ko Active pressure coefficient, Ka Passive pressure coefficient, Kp
γs = unit weight of soil
z = depth below the surface of earth
Force resultant is assumed to act at 0.4H from the base of wall
h sp k γ gz
48
Earth Pressure (EH)
49
Source: AASHTO (2002)
Surcharge Loads (ES and LS) Constant horizontal earth pressure due to surcharge load
is added to the basic earth pressure
ks = coefficient of earth pressure due to surcharge At-rest pressure coefficient, Ko Active pressure coefficient, Ka
qs = uniform surcharge applied to the upper surface of the active earth wedge
∆p s sk q
50
Loads on Abutment Live Load from Superstructure
51Source: Nowak (2005)
Loads on Abutment Earth Pressure and Surcharge Loads
Passive pressure is ignored
ConcreteApproachslab
O
H’
52Source: Nowak (2005)
Loads on Abutment Earth Pressure and Surcharge Loads
Passive pressure is ignored
Pv
Ph
ConcreteApproachslab
H’
0.4H’
O
Earth Pressure:Ph = ½ (EFPh)H’2
Pv = ½ (EFPv)H’2
Location at 0.4H’ instead of 1/3EFP = Equivalent Fluid Pressure
53Source: Nowak (2005)
Loads on Abutment Earth Pressure and Surcharge Loads
HL
Live load approach
WL
WD
HD
Passive pressure is ignored
Pv
VD
VL
Ph
ConcreteApproachslab
H’
0.5H’
0.4H’
O
Pressures generated by theLive Load and Dead Load Surcharges:HL = KwLH’HD = KwDH’VL = wL (heel width)VD = wD (heel width)wL = heq wD = slab thickness c
54Source: Nowak (2005)
Loads on Abutment Earth Pressure and Surcharge Loads
DLLL
BRCR+SH+TU
HL
Live load approach
WL
WD
HD
Passive pressure is ignored
Pv
VD
VL
Ph
ConcreteApproachslab
H’
0.5H’
0.4H’
O
Vertical Loads at the Bearing:DL and LLHorizontal Loads:BR (braking)CR (creep)SH (shrinkage)TU (temperature)
55Source: Nowak (2005)
Loads on Abutment Earth Pressure and Surcharge Loads
DLLL
BRCR+SH+TU
HL
Live load approach
WL
WD
HD
Passive pressure is ignored
Pv
VD
1
2
3
4
VL
Ph
ConcreteApproachslab
H’
0.5H’
0.4H’
O
Dead Load of theabutment
56Source: Nowak (2005)
Design of Pier Substructures
TypesFailure Limit States
LoadsDesign of RC Columns
57
Piers Pier substructures may be designed using design
procedures of columns Steel Concrete Composite
58Source: Chen and Duan (2003)
Piers Reinforced Concrete Piers
59Source: www.wikipedia.org (2005)
Piers Steel Truss Pier
60Source: www.wikipedia.org (2005)
Piers Piers may be
Solid – usually for short piers Hollow – usually for taller piers to save weight (need large
moment of inertia to prevent buckling and provide larger moment capacity for lateral loads)
Pier Types Solid Wall Pier Single Pier (Hammer Head Type) Rigid Frame
61
Pier Shapes
62Source: Chen and Duan (2003)
Piers
63Source: Chen and Duan (2003)
Pier Types – Steel Bridges
64Source: Chen and Duan (2003)
Pier Types – Steel Bridges Rigid Frame Pier
65
Pier Types – Concrete Bridges
66Source: Chen and Duan (2003)
Pier Types – Concrete Bridges
67
Pier Selection Factors that influences the selection of pier types
includes: Types of superstructures
Steel or Concrete Widths
Location Over land or water Hydraulics
Height (tall piers may be hollow to reduce weight) Space available Aesthetics
68
Pier Selection Guidelines
69
Source: Chen and Duan (2003)
Strength Limit States Pier structures must be checked for:
Global Stability Failure: Overturning
Local Strength Failures: Compression Failure Bending Moment Failure Shear Deflection
70
Source: Nowak (2005)
Loads on Piers from Superstructure Vertical loads from superstructures
Dead Load of Structural and Nonstructural Components (DC) Dead Load of Wearing Surface (DW) Live Load (LL) and Impact (IM) Pedestrian Live Load (PL)
Horizontal loads from superstructures Wind Load on Structures (WS) Wind Load on Live Load (WL) Earthquake Load (EQ) Vehicular Braking Force (BR), Centrifugal Force (CE), and
Collision Force (CT) Creep (CR), Shrinkage (SH), Friction (FR), and Temperature
(TG/ TU)71
Loads on Piers Itself Vertical load acting on substructure
Dead Load of Structural and Nonstructural Components (DC)
Horizontal loads acting on substructure Water Load and Stream Pressure (WA) Ice Load (IC) Wind Load on Structure (WS) Earthquake Load (EQ) Vehicular Collision Force (CT), Vessel Collision Force (CV)
72
Pier Load Analysis for Wind Loads
WS(on Substructure)
WS(on Superstructure)
WL
Investigate High Compressive ForceInvestigate High Bending (Low Compression) 73
Reinforced Concrete Columns Pure Axial (Ø=0.75)
Sprial
Tie
Pure Flexure (beam) (Ø=0.90 for RC)
Combined Axial and Flexure in on direction Interaction Diagram
00.85 0.85 0.85 ' ( )n c g st st yφP φ P φ f A A A f
00.80 0.80 0.85 ' ( )n c g st st yφP φ P φ f A A A f
( / 2)n s yφM φA f d a
74
Reinforced Concrete Columns Spiral vs. Tie columns
75Source: Wang et. al. (2006)
Axial Loads + Bending Moment
76Source: Chen and Duan (2003)
Reinforced Concrete Columns Biaxial Bending + Axial
For high axial load
For low axial load
For slender columns, must also determine the secondary moment due to P-∆ Effect
0.1 'u c gP φf A
0.1 'u c gP φf A
0
1 1 1 1
rxy rx ryP P P P
1.0uyux
rx ry
MMM M
Factored Applied Moment in X and Y direction
Factored Nominal Moment Capacity in X and Y direction
Factored Axial Resistance when has eccentricity only in Y direction
Factored Axial Resistance when has eccentricity only in X direction
77