Quick-Release Field Experiments on Seismically Isolated Bridges

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Quick-Release Field Experiments on Seismically
Isolated Bridges

• Stuart S. Chen, Ph.D., P.E.
• Associate Professor, University at Buffalo
  (SUNY),
• Fulbright Senior Lecturer, ITU

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Presentation Outline

• Comprehensive Study Overview
• Bridges Studied
• Loading and Instrumentation Apparatus
• Selected Results
• Anticipating Seismic Performance
• Summary, Conclusions, Recommendations
• Acknowledgements

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Comprehensive Study! Overview

• Two Similar Bridges, Before and After Seismic
  Retrofit with Isolation Bearings
• Field (System Quick-Release) and Laboratory
  (Component Reverse-Cyclic) Experiments
• Comparing Analytical vs. Experimental Dynamic
  Behavior
• Inferring Seismic Performance from Calibrated
  Models

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Seismic Isolation Concept
(Kelly, 2001)
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Seismic Isolation Concept (contd)
(Kelly, 2001)
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Bridges Plan View
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Bridges Elevation Brg. Schedule
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Bridge Cross Sections
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Bridge Bearing Replacement (Abut.)
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Bridge Bearing Replacement (Pier)
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Installing Isolation Brgs at Abutments
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Southbound Abutment Isolator
Kelly, 2001
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Southbound Pier Isolator
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Northbound Expansion Bearing (non-seismic)
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Northbound Bridge Bearings
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Objectives

• Measure and assess in-situ dynamic behavior and
  performance of typical slab- on- girder bridge
  subjected to transverse quick-release loading
  (steel brgs vs. seismic isolation brgs vs.
  standard laminated elastomeric brgs)
• Quantify in-situ dynamic performance change
  attributable to bearing retrofits

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Objectives, contd

• Quantify Winter-Weather Effects on In-Situ
  Performance of Isolation and Elastomeric Bearings
• Assess Relative Merits of Several Modeling
  Approaches (at varying levels of complexity) in
  predicting transverse transient dynamic behavior
  of straight skewed slab-on-girder bridge
  structures

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Loading Scheme
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Loading Scheme (contd)
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Loading Scheme (contd)
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Loading Scheme (contd)
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Loading Scheme (contd)
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Loading Scheme (contd)
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(Under-Bridge) Loading Scheme!
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Loading Scheme (contd)
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Loading Scheme The Importance of Genuinely Quick
Release!
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Loading Scheme Mechanical Fuse
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Loading Scheme Mechanical Fuse in Place
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Selected Instrumentation
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Selected Instrumentation (contd)
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Selected Instrumentation (contd)
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Selected Instrumentation (contd)
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Selected Instrumentation (contd)
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Selected Instrumentation (contd)
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Selected Results Free Vibn
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Pre-Retrofit in Frequency Domain
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1st 2 Pre-Retrofit Mode Shapes
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SAP Model
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DRAIN-2DX Model
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3rd Pre-Retrofit Mode Shape
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Seismic Isolation Concept Recall!
Sd
Sa
?
T
T
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Post- Retrofit Time- History at Abutment
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Post-Retrofit SB (Linear Portion 2)
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Post-Retrofit SB contd (Linear Portion 2)
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Post-Retrofit NB (Linear Portion 2)
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Post-Retrofit NB contd (Linear Portion 2)
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Selected NB Post-Retrofit T-Hs
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Post-Retrofit SB contd
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Post-Retrofit SB (Nonlinear Portion 1)
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Time, Temperature, Setup Effects (SB)
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Old Steel Bearings Not So Bad After All!
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C/D vs. PGA, Pre-Retrofitted
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C/D vs. PGA, Post-Retrofitted
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Summary, Conclusions, Recommendations

• Transverse Quick-Release Experiments are
  successfully executed using the deployed
  apparatus
• Replacement of the original steel bearings with
  seismic isolation bearings leads to substantial
  behavior changes (period shift, etc.) in the
  transverse direction, as predicted. However,
• Due to reserve strength of columns and steel
  bearings, actual seismic resistance of the
  retrofitted southbound bridge is not greatly
  increased by its seismic isolation retrofit, and
• The torsional behavior induced in the retrofitted
  northbound bridge nullifies the otherwise
  seismically beneficial effect of its standard
  (non-seismic) elastomeric bearing retrofit

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Summary, Conclusions, and Recommendations (contd)

• Neither a 3D Model nor formal structural
  identification methods produce any significant
  advantages over 2D modeling as long as nonlinear
  behavior is incorporated into the model
  (DRAIN-2DX)
• Cold-weather effects in western NY are not
  sufficiently severe to have a significant
  influence on LRB seismic isolation behavior

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Acknowledgements

• J. B. Mander, D. Wendichansky, G. Pekcan, D.-K.
  Kim, I.-S. Ahn, L. Zhang, P. Dreyer, etc.
• New York State Dept. of Transportation, Union
  Concrete and Construction Corp.
• U.S. D.O.T. / Federal Highway Administration
  funding through NCEER/MCEER at the University at
  Buffalo