Computational Analyses of Quasi-Isolated Bridges with ...jfhajjar/home/768 Filipov et al. -- Bridge... · Computational Analyses of Quasi -Isolated Bridges with Fusing Bearing Components

Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components

Evgueni T. Filipov – Graduate Research Assistant , Department of Civil & Environmental Engineering (CEE), University of Illinois

Jerome F. Hajjar – Professor, and Chair, CEE, Northeastern University

Joshua S. Steelman – Graduate Research Assistant , CEE, University of Illinois

Larry A. Fahnestock – Professor, CEE, University of Illinois

James M. LaFave – Professor, CEE, University of Illinois

Douglas A. Foutch – Professor Emeritus, CEE, University of Illinois

2011 ASCE SEI Structures CongressApril 16, 2011 - Las Vegas, Nevada

Illinois Departmentof Transportation

Illinois Centerfor Transportation


Introduction IDOT Earthquake Resisting System (ERS): Recently developed & adopted design approach

tailored to typical Illinois bridge types (and in part addressing increased hazard levels in AASHTO) Primary objective: Prevention of span loss Three levels of design and performance:

» Level 1: Connections between super- and sub-structures designed to provide a nominal fuse capacity

» Level 2: Provide sufficient seat widths at substructures to allow for unrestrained superstructure motion

» Level 3: Plastic deformations in substructure and foundation elements (where permitted)

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Quasi-Isolation for Bridges Typical bridge bearing systems designed to act as fuses to

limit the forces transmitted from the superstructure to the substructure Type I bearings: bearings with an elastomer to concrete sliding surface Type II bearings: elastomeric bearings with PTFE sliding surface L-shaped retainers: designed to limit service load deflections Low-profile bearings with steel pintles and anchorbolts

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Elastomeric bearing on concrete Elastomeric bearing with PTFE sliding surface

Low-profile fixed bearing

BRIDGE BEAM

STEEL TOP PLATE

TYPE I ELASTOMERICBEARING WITH STEELSHIMS

RETAINER

CONCRETESUBSTRUCTURE

ANCHOR BOLT

BRIDGE BEAM

TOP PLATE WITH POLISHEDSTAINLESS STEEL SURFACE

PTFE SURFACE


RETAINER

ANCHOR BOLT

TYPE II ELASTOMERICBEARING WITH STEEL SHIMS

BRIDGE BEAM

PINTLE

LOW-PROFILE FIXEDBEARING

ANCHOR BOLT



Bridge Prototype Model Three 50’ spans with six W27x84 Gr. 50 composite girders and

8” concrete deck 15’ Tall multi-column intermediate substructures Concrete abutments with backwalls and 2” gap from deck Pile foundations for all substructures

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Bridge Prototype Plan

Mesh Representation of OpenSees Model Bridge Prototype Elevation

42'-0

"

50'-0" 50'-0" 50'-0"

15'-0

"

LOW-PROFILEFIXED BEARINGS

TYPE I - ISOLATIONBEARINGS

W27x84

ABUTMENT

MULTI-COLUMNPIER

Type I - Bearings

Low-profile fixed bearings


Modeling of Bearing Components

Sliding elastomeric bearing modelsOngoing experimentation is studying behaviorDifference in static vs. kinetic coefficient of

frictionFriction slip-stick behavior noted in cases

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-200 -100 0 100 200

-100

-80

-60

-40

-20

0

20

40

60

Displacement (mm)

Forc

e (k

N)

Bearing Type I; Exp.#5x1

Model:µSI=0.35; µSP=0.33; µK=0.24

0 50 100 150 2000

10

20

30

40

50

60

70

Displacement (mm)

Forc

e (k

N)

Bearing Type I; Exp.#1

Model:µSI=0.37&µK=0.29Bearing Type II; Exp.#9

Model:µSI=0.14&µK=0.06


Bi-directional bearing elements Dependent on axial force Allows for initial capacity and different pre and post-slip

static coefficients of friction Force-displacement behavior coupled in orthogonal shear

directions Kinematic-hardening surface used to trace bearing

movement

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Combined Force

Combined Displacement

FK

ΔINITIALBREAK

ΔSLIDE

EINITIAL

ΔFRICBREAK

FSI + FINITIAL

2 2_1 _1X ZF F+ FSP

2 2_1 _1X Z∆ + ∆

EFRIC

Z

XStatic condition if (ΔX_1, ΔZ_1) is within dashed circle

ΔP_X_0 ΔX_0

ΔP_Z_0

ΔZ_0

ΔSLIDE

ΔFRIC_BREAK

θ0

θ1

(ΔX_1, ΔZ_1)


Retainer simulation for System Analyses Gap with elasto-plastic response until

retainer fracture Independent behavior of the (2)

retainers Calibrated based on experiments and

Finite Element Modeling

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0 10 20 30 40 50 60 70

0

20

40

60

80

100

120

140 p

Displacement (mm)

Forc

e (k

N)

Experiment # 7Retainer Model

Modeling of Bearing Retainers


Intermediate SubstructuresBeam-column elements with lumped plasticity

at nodesFiber sections used to model nonlinear

behavior at hinge locations of column

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-0.1 -0.05 0 0.05 0.1

-250

-200

-150

-100

-50

0

50

100

150

200

250

Top Node Displacement (m)

Forc

e (K

N)

UncrackedCracked ElasticCracked Inelastic

Column pier substructure with lumped plasticity at beam hinges

Linear elastic pier cap

Nodes for bearing attachment to substructure

Linear elastic pile cap

lp


Foundations and Backwalls

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-0.08 -0.07 -0.06 -0.05 -0.04 -0.03 -0.02 -0.01 00

5000

Left Abutment Backwall

Displacement (m)

For

ce (

KN

)

5cm (2") Expansion Gap

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.080

5000

Right Abutment Backwall

Displacement (m)

For

ce (

KN

)

5cm (2") Expansion Gap

Substructure

Lateral Stiffness

Rotational Stiffness

Axial Stiffness

0”

Springs to model local abutment foundation

5cm (2”) Gap Element

Rigid Link representing backwall

Zero length element allowing plastic hinge capability of backwall

Hyperbolic Gap element with 0cm(0”) gap

Node at bottom of bearing

Zero length elements representing bearing and retainer connectivity

Node for local abutment behavior

Superstructure assembly

Deck node

Pile group analysis performed to develop nonlinear force-displacement representation of foundations

Hyperbolic gap material used to model backwall interaction


Limit State Identification Longitudinal

Bearings Elastomer deformation & nonlinear behavior Yielding and fracture in anchor bolts & pintles of fixed bearings Sliding of bearings on substructure

Column and wall piers Cracking of concrete Yielding of reinforcement Crushing of concrete

Foundations Plastic deformation of backwall & backfill Plastic deformation of pile groups & pile caps

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Longitudinal Analysis

11

Limit state identification stiff foundation 2500 yr Paducah ground motion

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Longitudinal Analysis Slip of bearings at abutments

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Longitudinal Analysis Yielding in substructure #2, backwall interaction, and plastic

deformation in foundation

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Longitudinal Analysis Slip of bearings at pier #1

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Limit State Identification Transverse

Bearings Elastomer deformation, retainer deformation with fracture &

nonlinear bearing behavior Yielding and fracture in anchor bolts & pintles of fixed bearings Sliding of bearings on substructure

Column and wall piers Cracking and/or crushing of concrete Yielding of reinforcement

Foundations Plastic deformation of pile groups & pile caps Possible interaction with backwall & backfill

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Transverse Analysis

16

Limit state identification fixed foundation 2500 yr Paducah ground motion (only 8 Seconds)

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Transverse Analysis Plasticity in retainers and bearing slip at abutment # 1

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Transverse Analysis

18

Fracture of retainer component

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Transverse Analysis

19

Fracture of fixed bearing

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System Analyses ObjectivesQuantification of expected value and dispersion for:Peak & residual bearing displacements Peak force demands on fuse componentsPeak force demands on sub-structuresSequence of fuse & systems failure

Parametric study to investigate influence of: Superstructure length and typeSubstructure height and type (column pier & wall)Isolation bearings (Type I & Type II) Foundation characteristics (stiff & soft soils)

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Summary & ConclusionsNew element models represent key aspects of local

bearing behaviorsGlobal bridge model captures limit states for a

realistic three dimensional analysis Flexibility of elastomeric bearings and sliding of

bearings allows for quasi-isolated response Retainer elements and low-profile bearings need to

be carefully detailed to limit forces on substructures Backwalls have a significant contribution in limiting

longitudinal displacements

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Computational Analyses of Quasi-Isolated Bridges with ...jfhajjar/home/768 Filipov et al. -- Bridge... · Computational Analyses of Quasi -Isolated Bridges with Fusing Bearing Components