Bridge ComponentsBridge Components

Loading Codal ProvisionsLoading Codal Provisions

Suhasini Madhekar Suhasini Madhekar

College of Engineering PuneCollege of Engineering Pune

Faculty Development Program onFaculty Development Program on

Fundamentals of Structural Dynamics and Application to Fundamentals of Structural Dynamics and Application to

Earthquake EngineeringEarthquake Engineering

1212thth December 2015December 2015

Sanjay Sanjay GhodawatGhodawat Group of InstitutionsGroup of Institutions

AtigreAtigre, Kolhapur, Kolhapur 11

Bridge Components Bridge Components

Bridge Bearings: Supported on a bridge pier, which carry the

weight of the bridge and control the movements at the bridge

supports, including the temperature changes.

Types : Metal rockers, rollers or slides or merely rubber or

laminated rubber, POT - PTFE

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laminated rubber, POT - PTFE

Bridge Dampers & Isolators: To absorb energy generated by

earthquake waves and lateral load

Bridge Pier: A wide column or short wall of masonry or plain

or RCC for carrying loads as a support for a bridge, founded

on firm ground

Bridge Cap: The highest part of a bridge pier on which the

bridge bearings or rollers are seated.

Bridge Deck: The load bearing floor of a bridge which carries

and spreads the loads to the main beams. (RCC / PSC /

Steel plate girder / Composite)

Bridge Components Bridge Components

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Steel plate girder / Composite)

Abutment: A support of bridge which may carry a horizontal

force as well as weight.

Expansion Joints : These are provided to accommodate the

translations due to possible shrinkage and expansions due to

temperature changes.

Bridge Bridge -- ComponentsComponents

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Bridge ComponentsBridge Components

Foundation

SubstructureWell Cap

Pier Cap

Superstructure

Soil Stratum

Bearings

(Connections)

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The FOUR Components::Foundation :: Well and Well Cap; Pile and Pile Cap

Substructure :: Pier(s) and Pier Cap; Wall; Frame

Connections :: Fixed, Free and Guided Bearings

Superstructure :: Slab; Girder-Slab; Box; Truss; Frame

Soil Stratum

Bridge Cap and DamperBridge Cap and Damper

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Loading on BridgesLoading on Bridges

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Cars on a suspension bridge over a Cars on a suspension bridge over a river : Coloradoriver : Colorado

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• Permanent Loads: remain on the bridge for an

extended period of time (self weight of the bridge)

• Transient Loads: loads which are not permanent

Loading on BridgesLoading on Bridges

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- gravity loads due to vehicular, railway and

pedestrian traffic

- lateral loads due to water and wind, ice, ship collision,

earthquake, etc.

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Mass of deck = 3,278,404 kg ( DL = 32784 kN)

LL = 3850 kN

D = 65658 kN, F= 324 kN

• Bridge Vibration Units:

– Single-span

– Multi-span

• Simply-supported

Behaviour: Longitudinal shakingBehaviour: Longitudinal shaking

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• Continuous

Overall Structural Behaviour

Behaviour: Transverse shakingBehaviour: Transverse shaking

SuperstructureConnections

•Vertical cantilever action

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Substructure

Foundation

•Vertical cantilever action

•Mass lumped at the top

•Foundation flexibility

Ductile Link

Plastic Moment

Capacity Design of Bridge ComponentsCapacity Design of Bridge Components

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Ductile Link

Brittle Link

Moment Hinges

•Damage only in piers: mandatory ductile detailing•Elastic design of other components

Gawana Bridge (1991 Uttarkashi Earthquake)- Shearing off of anchor bolts of roller–cum–rocker bearings

Bridge Performance in past Indian Earthquakes Bridge Performance in past Indian Earthquakes

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Past EQs...Past EQs...

Gawana Bridge…- Unseating of superstructure from abutments

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Past EQs…Past EQs…

Gawana Bridge…

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Past EQs…Past EQs…

Old Surajbadi Bridge (2001 Bhuj Earthquake)- Bearing damage due to jumping of superstructure

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Past EQs…Past EQs…

New Surajbadi Bridge (2001 Bhuj Earthquake)- Jumping of Girders – Damage to girders

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Toe Crushing of Stone Wall Masonry Piers- Old Highway bridge (2001 Bhuj earthquake)

Past EQs…Past EQs…

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Vertical Splitting of Stone Wall Masonry Piers- Old Highway bridge (2001 Bhuj earthquake)

Past EQs…Past EQs…

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Collapse of Superstructure- Aman Setu (2005 Kashmir earthquake)

Past EQs…Past EQs…

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Analysis of Bridges : Issues in ModelingAnalysis of Bridges : Issues in Modeling

• Superstructure– No ductility demand – Usually, stiff in vertical direction

• Connections– Simple Bearings :: Rocker, Roller

• Model as rigid, with usual freedom

– Flexible Bearings :: Neoprene/Rubber/Lead Rubber

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– Flexible Bearings :: Neoprene/Rubber/Lead Rubber• Model as Flexible

• Substructure– Only structural component with ductility

• Detailed idealisation required

– Effect of shear deformations to be included

• Foundation– Main concern is modeling soil

• Levels of earthquake shaking

– LOW :: Functional Evaluation Earthquake

• Un-cracked Section (EIgross)

– HIGH :: Safety Evaluation Earthquake

• Cracked Section (EIeff)

Properties for ModelingProperties for Modeling

M

EI

EIgross

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Natural Period T (sec)

0.0

0.5

1.0

1.5

2.0

0 1 2 3 4

Sp

ectr

al A

ccele

rati

on

Sa/g Safety

Functional

Mu

0.6Mu

EIeff

ϕ

• Modulus of Subgrade Reaction k

– Layered Soil

– “N” Value

Properties for modeling…Properties for modeling…

Rigid Foundation

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Distributed Springs Lumped Springs

Foundation

Modeling: SummaryModeling: Summary

35Cantilever model for Transverse Shaking

Overall model

for Longitudinal Shaking

AnalysisAnalysis

• Methods of Dynamic Analysis

Seismic Coefficient method

Response Spectrum analysis for other bridges

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Time History analysis for special bridges

Push over analysis

Geometric and material nonlinearities

IRC Codes: Flexure and Shear Design IRC Codes: Flexure and Shear Design

• Design lateral force calculation

(Interim IRC: 6-2014)

- Structural flexibility

- Response Reduction Factor (R) for nonlinear response

• Working Stress Design for bridge substructures

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• Working Stress Design for bridge substructures (IRC:21-2000)

- Not applicable for explaining seismic behaviour

- Contradiction with the lateral force calculation method

IRC Codes: Flexure and Shear Design… IRC Codes: Flexure and Shear Design…

• No provision on explicit design against lateral shear force (IRC:21-2000)

- Shear design prescribed only for beams and slabs

- Horizontal steel provided as per the prescribed minimum amount

- No provision on confinement of concrete

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- No provision on confinement of concrete

• Capacity design not prescribed for any bridge component (IRC:21-2000, IRC:78-2000)

- No plastic hinge formation in case of extreme seismic event

• Limit State Design for bridge (IRC:112 -2011)

IRC Codes: Flexure and Shear Design… IRC Codes: Flexure and Shear Design…

• Wall piers and column piers (IRC:78-2000)

- No difference in design methodologies

Pier Cap

Pier Cap

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:: Flexural deformations:: Plastic Hinge Region

Column Pier

Pile Cap

Wall Pier

Pile Cap

:: Shear deformations:: No plastic hinge

IRC Codes: Flexure and Shear Design… IRC Codes: Flexure and Shear Design…

• Well Foundations (IRC:78-2000)

- Three dimensional finite element analysis of the foundation

- Tensile and compressive stresses checked at the critical

sections

- No formal flexure and shear design methodology prescribed

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prescribed

- Nominal vertical and horizontal steel prescribed

- Proportioning of foundation prescribed on an empirical basis

- Seismic design procedure not available

•Generated where the mass is (at deck level)

• Needs to be transferred safely to ground

Earthquake Force…Earthquake Force…

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• Vertical vibrations

– Vertical inertia force

– Adds and subtracts to the gravity force

– Generally not a problem due to FS in gravity design

Ground vibrations…Ground vibrations…

42Gravity LoadsGravity Loads Vertical EQ-Induced Inertia ForceVertical EQ-Induced Inertia Force

•Horizontal vibrations

Horizontal inertia force

Need load transfer path

Need adequate strength

Ground vibrations…Ground vibrations…

Deck Slab

Piers

Inertia Forces

43Flow of EQ inertia forces through all componentsFlow of EQ inertia forces through all components

Soil

Earthquake Shaking

Piers

Foundations

SuperstructureSuperstructure

ConnectionsConnections

• The Bridge Example

Capacity Design ConceptCapacity Design Concept

EQ Design– Good Ductility

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SubstructureSubstructure

FoundationFoundation

– Good Ductility

– Adequate Strength

(FEQ)max

P

• The Bridge Example…

The Example…The Example…

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M(FEQ)max

P

Shear Design

( )max

0

EQ

MF

H=

(FEQ)max

PH

• The Bridge Example…

The Example…The Example…

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0H

M(FEQ)max

PH0

( )max

EQ uIf F V>

design additional steel for the balance shear

Plastic

The Example…The Example…

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Ductile Link

Brittle Link

Plastic Moment Hinges

Reinforced concrete bridgeReinforced concrete bridge ::

Slab bridge: span < 12 m

Carriageway

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Slab

Cross section of solid slab bridge deckCross section of solid slab bridge deck

Reinforced concrete bridgeReinforced concrete bridge ::

T-Beam bridge : span 12 to 24 m

Carriageway

Footpath

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49Cross section of TCross section of T--beam bridge deckbeam bridge deck

D=1200-1800 mm

T-beam Cross beam

Reinforced concrete bridgeReinforced concrete bridge ::

Slab on girder bridge :Footpath

Carriageway

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50Cross section of ICross section of I--beam bridge deck beam bridge deck

I-beam

D=1200-3000 mm

Cross beam (Diaphragm)

Reinforced concrete bridgeReinforced concrete bridge ::

Box girder bridge : span: 20 to 50 m

Carriageway

Footpath

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51Cross section of box girder bridge deck Cross section of box girder bridge deck

D= 1000-3000 mm

Steel bridgeSteel bridge ::

Steel I-beam bridge : Span: upto 20 m

Footpath

Carriageway

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52Cross section of steel ICross section of steel I--beam bridge deck beam bridge deck

Common types of failure observed under seismic excitation:Common types of failure observed under seismic excitation:

Seismic displacement failure

Abutment slumping failure

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Abutment slumping failure

Column failure

Joint failure

Displacement failure : UnseatingDisplacement failure : Unseating

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Unseating failure of main approach of Nishinomiyako bridge in Kobe earthquake (Japan)

Displacement failure: Pounding Displacement failure: Pounding

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The longitudinal movement of the new Surajbadi bridge superstructures led to pounding at the deck slab

level in Bhuj Earthquake, 2001 India.

Abutment Slumping failure Abutment Slumping failure

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Pile foundation

Deck

Column failure due to improper detailing of plastic hinge region Column failure due to improper detailing of plastic hinge region

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Crushed column of Santa Monica Freeway

Northridge earthquake 1994 (USA)

Column failure due to improper detailing of plastic hinge regionColumn failure due to improper detailing of plastic hinge region

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Column failure in Mission-Gothic under crossing at Simi Valley

San Fernando Freeway in Northridge earthquake 1994, USA

Column shear failure.Column shear failure.

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Failure of column of Hanshin Expressway, Japan in

Kobe Earthquake, 1995 Japan.

Joint failure due to poor detailing Joint failure due to poor detailing

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Cypress viaduct joint failure in

Northridge earthquake in 1994 USA .

Conceptual seismic designConceptual seismic design::

The bridge should be straight as curve bridge complicates the

seismic response.

Deck should be continuous with few movement joints. Simply

supported spans are prone to unseating.

Foundation material should be of rock or firm alluvial. Soft soil

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Foundation material should be of rock or firm alluvial. Soft soil

amplifies seismic response.

Pier height should be constant along the bridge. Non-uniform

height results in stiffness variation and attraction of more

forces to stiffer pier.

Pier stiffness should be uniform in all direction.

Conceptual seismic designConceptual seismic design::

Span length should be kept short. Long span results in

high axial forces on the column with potential for reduced

ductility.

Plastic hinges should be developed in the column rather

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Plastic hinges should be developed in the column rather

than in the cap beam or in superstructure.

The abutment and the pier should be oriented

perpendicular to the bridge axis. Skew supports tend to

cause rotational response with increased displacement.

Connection of pier and superstructure Connection of pier and superstructure ::

Bearing

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(a) Moment resisting conection

Bearing

(b) Bearing supported connection

Support alternative for pier and superstructure

Beneficial effect of consideration of soil flexibility Beneficial effect of consideration of soil flexibility

Consideration of soil flexibility effect on foundation gives

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lesser forces due to shift of period of vibration of structure

because of added flexibility by soil from higher acceleration

zone to lower acceleration zone of design spectrum.

Outcome:Outcome:

The substructure of bridge are more vulnerable under

seismic excitation.

Non consideration of inelastic action of structure led to the

failures in plastic hinge region of column.

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Seismic deflection of bridge calculated using elastic theory

of design will lead to underestimation of actual deflection

and will result into unseating or pounding of girders during

seismic excitation.

Outcome (contd..) Outcome (contd..)

Comparative study of possible alternative models of same

type of bridge are required

Comparative results of fixed base and detailed model for

bridge with well foundation considering SSI

Difference in seismic response of bridge model with actual

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Difference in seismic response of bridge model with actual

and simplified location of bearing

Effect of scour of river bed on seismic response

Effect of hydrodynamic pressure on seismic response using

global model.

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Thank you..