Seismic Response of Bearings for Quasi-Isolated Bridges Joshua S. - - PowerPoint PPT Presentation

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Seismic Response of Bearings for Quasi-Isolated Bridges Joshua S. - - PowerPoint PPT Presentation

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2011 ASCE SEI Structures Congress April 16, 2011 Las Vegas, Nevada Seismic Response of Bearings for Quasi-Isolated Bridges Joshua S. Steelman Graduate Research Assistant , Department of Civil & Environmental Engineering (CEE),

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Seismic Response of Bearings for Quasi-Isolated Bridges

Joshua S. Steelman – Graduate Research Assistant , Department of Civil & Environmental Engineering (CEE), University of Illinois Larry A. Fahnestock – Assistant Professor, CEE, University of Illinois James M. LaFave – Associate Professor, CEE, University of Illinois Jerome F. Hajjar – Professor and Chair, CEE, Northeastern University Evgueni T. Filipov – Graduate Research Assistant , CEE, University of Illinois Douglas A. Foutch – Professor Emeritus, CEE, University of Illinois 2011 ASCE SEI Structures Congress April 16, 2011 – Las Vegas, Nevada Illinois Department

  • f Transportation

Illinois Center for Transportation

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SLIDE 2

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)

9/24/2010 2 Calibration and Refinement of Illinois' Earthquake Resisting System Bridge Design Methodology

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SLIDE 3

Experimental Testing Program

  • Characterize behavior of unrestrained elastomeric bearings

 Relative importance of slip, instability, and bond of internal shims

04/16/2011 3 Seismic Response of Bearings for Quasi-Isolated Bridges

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Experimental Testing Program

  • Transverse response including retainer response at large

displacements

04/16/2011 4 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 5

Experimental Testing Program

  • Elastomeric bearings with Teflon sliding layer

04/16/2011 5 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 6

Experimental Testing Program

  • Sequence of damage progression for fixed-bearings

04/16/2011 6 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 7

Experimental Testing Set-Up

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Horizontal Actuator Stroke = +/- 15” Pair of vertical actuators maintain constant vertical load with varying horizontal bearing position Concrete pad simulates substructure surface Bearing Specimen

Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 8

Experimental Observations

  • Initial observations suggest slip is most

significant influence during large earthquake

04/16/2011 8 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 9

Experimental Observations

  • Initial observations suggest slip is most

significant influence during large earthquake

04/16/2011 9 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 10

Experimental Observations

  • Limited damage observed with repeated tests
  • n single bearing

04/16/2011 10 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 11

Experimental Observations

  • Higher compression  Higher friction break-
  • ff force & larger displacement to induce slip

04/16/2011 11 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 12

Experimental Observations

  • Inverse relationship between compression

stress and friction limit

04/16/2011 12 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 13

Experimental Observations

  • Inverse relationship between compression

stress and friction limit

04/16/2011 13 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 14

Experimental Observations

  • Inverse relationship between compression

stress and friction limit

04/16/2011 14 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 15

Experimental Observations

  • 200 psi compression
  • 7”x12” elastomer

04/16/2011 15 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 16

Experimental Observations

  • 200 psi compression
  • 7”x12” elastomer

04/16/2011 16 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 17

Experimental Observations

  • 200 psi compression
  • 7”x12” elastomer

04/16/2011 17 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 18

Experimental Observations

  • 500 psi compression
  • 7”x12” elastomer

04/16/2011 18 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 19

Experimental Observations

  • 500 psi compression
  • 7”x12” elastomer

04/16/2011 19 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 20

Experimental Observations

  • 500 psi compression
  • 7”x12” elastomer

04/16/2011 20 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 21

Experimental Observations

  • 800 psi compression
  • 7”x12” elastomer

04/16/2011 21 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 22

Experimental Observations

  • 800 psi compression
  • 7”x12” elastomer

04/16/2011 22 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 23

Experimental Observations

  • 800 psi compression
  • 7”x12” elastomer

04/16/2011 23 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 24

Experimental Observations

  • 385 psi compression
  • 13”x20” elastomer

04/16/2011 24 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 25

Experimental Observations

  • 385 psi compression
  • 13”x20” elastomer

04/16/2011 25 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 26

Experimental Observations

  • 385 psi compression
  • 13”x20” elastomer

04/16/2011 26 Seismic Response of Bearings for Quasi-Isolated Bridges

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Experimental Observations

  • Single retainer tests

04/16/2011 27 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 28

Experimental Observations

  • Single retainer tests

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SLIDE 29

Experimental Observations

  • Single retainer tests

04/16/2011 29 Seismic Response of Bearings for Quasi-Isolated Bridges

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Experimental Observations

  • Small retainer test

04/16/2011 30 Seismic Response of Bearings for Quasi-Isolated Bridges

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SLIDE 31

Experimental Observations

  • Small retainer test

04/16/2011 31 Seismic Response of Bearings for Quasi-Isolated Bridges

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Experimental Observations

  • Large retainer test

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Experimental Observations

  • Small vs Large retainers

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SLIDE 34

Experimental Observations

  • Small vs Large retainers

04/16/2011 35 Seismic Response of Bearings for Quasi-Isolated Bridges

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Conclusions

  • Type I bearings shown to be remarkably resilient

 Stable friction hysteresis with multiple fully reversed cycles  Visible abrasions at friction interface  Scragging and deterioration have minor effect on performance

  • Type I bearings tolerate approx. 100 – 200% equivalent shear

strain without slip

 Proportionately related to compression load

  • Friction break-off coefficient approx. 0.25 – 0.5

 Inversely related to compression load

  • Retainer fuse strength currently significantly underestimated

 Capacity closer to ultimate tensile strength of anchor, instead of shear

  • r combined shear & tension strength

 Underestimation more severe for smaller anchors

04/16/2011 36 Seismic Response of Bearings for Quasi-Isolated Bridges