PACIFIC EARTHQUAKE ENGINEERING RESEARCH CENTER PACIFIC EARTHQUAKE ENGINEERING Simulation and Performance-Based Earthquake Engineering Assessment of Self-Centering Post-Tensioned Concrete Bridge Systems Won K. Lee and Sarah L. Billington Stanford University PEER 2009/109 DECEMBER 2009 Simulation and Performance-Based Earthquake Engineering Assessment of Self-Centering Post-Tensioned Concrete Bridge Systems Won K. Lee Department of Civil and Environmental Engineering Stanford University Sarah L. Billington Department of Civil and Environmental Engineering Stanford University PEER Report 2009/109 Pacific Earthquake Engineering Research Center College of Engineering University of California, Berkeley December 2009 ABSTRACT The focus of this research is on conducting a performance-based earthquake engineering assessment of self-centering bridge columns for structural concrete bridges. Standard highway bridges in highly seismic regions are typically designed for columns to undergo large inelastic deformations during severe earthquakes, which can result in residual displacements. These residual displacements are a measure of post-earthquake functionality in bridges, and can determine whether a bridge remains usable following an earthquake. To mitigate the effects of residual displacements, a number of self-centering systems for bridge columns using unbonded post-tensioned (UBPT) reinforcing steel are proposed and investigated. The research reported herein had three objectives: (1) to assess and develop simulation methods and models that can accurately capture key performance attributes of reinforced concrete and unbonded post- tensioned concrete bridge piers, to facilitate their comparison; (2) to provide a systematic assessment of various self-centering bridge column systems in terms of engineering performance, as well as expected repair costs and downtime, including a quantitative comparison to current code-conforming reinforced concrete bridge designs using the performance-based earthquake engineering methodology developed by the Pacific Earthquake Engineering Research Center; and (3) to evaluate the performance-based earthquake engineering methodology itself. The unbonded post-tensioned systems were found to perform comparably to the conventional reinforced concrete system in terms of peak drifts. Reductions to column damage in the case of some of the systems were found not to justify their higher initial costs. However, the unbonded post-tensioned columns sustained considerably lower residual drifts than the reinforced concrete columns, leading to significant reductions in expected bridge downtime following large earthquakes. These significant reductions in downtime make the unbonded post-tensioned systems desirable for important bridges that must remain operational following an earthquake. iii ACKNOWLEDGMENTS This work was supported primarily by the Earthquake Engineering Research Centers Program of the National Science Foundation, under award number EEC-9701568 through the Pacific Earthquake Engineering Research (PEER) Center. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect those of the National Science Foundation. The authors would like to acknowledge their fellow collaborators in bridge research on this project for their insights and participation: Professors Stephen Mahin, Boza Stojadinovic, John Stanton, Kevin Mackie, and Dr. Junichi Sakai. The assistance of Dr. Polsak Tothong with ground motion selection and probabilistic seismic hazard analysis is gratefully acknowledged. iv CONTENTS ABSTRACT.................................................................................................................................. iii ACKNOWLEDGMENTS ........................................................................................................... iv TABLE OF CONTENTS ..............................................................................................................v LIST OF FIGURES ..................................................................................................................... xi LIST OF TABLES ..................................................................................................................... xix 1 INTRODUCTION .................................................................................................................1 1.1 Motivation.......................................................................................................................1 1.2 Objectives........................................................................................................................2 1.3 Organization....................................................................................................................3 2 BACKGROUND AND LITERATURE REVIEW.............................................................5 2.1 Introduction.....................................................................................................................5 2.2 PEER’s PBEE Methodology...........................................................................................5 2.2.1 Hazard Analysis..................................................................................................8 2.2.2 Structural Analysis..............................................................................................9 2.2.3 Damage Analysis..............................................................................................10 2.2.4 Loss Analysis....................................................................................................11 2.2.5 Summary of PEER PBEE Methodology...........................................................11 2.3 Post-Earthquake Functionality of Reinforced Concrete Bridges..................................12 2.4 Self-Centering Systems.................................................................................................14 2.5 High-Performance Fiber-Reinforced Cement Composites ...........................................18 2.5.1 Introduction to HPFRCC ..................................................................................18 2.5.2 ECC Material Behavior and Composition ........................................................19 2.5.3 Mechanical Behavior........................................................................................20 2.5.3.1 Monotonic Tensile Behavior..............................................................21 2.5.3.2 Monotonic Compressive Behavior.....................................................22 2.5.3.3 Cyclic Behavior..................................................................................23 2.5.3.4 Load Rate Effect.................................................................................25 2.5.3.5 Test Specimen Shape and Other Effects.............................................25 2.5.4 Structural Applications .....................................................................................26 v 2.5.5 Summary of HPFRCC Material Literature Review..........................................27 3 SIMULATION OF PRECAST SEGMENTAL UBPT COLUMNS...............................29 3.1 Introduction...................................................................................................................29 3.2 Simulation of UBPT Bridge Columns with HPFRCC and Concrete Hinges ...............30 3.2.1 Objectives..........................................................................................................30 3.2.2 Background on Experiments.............................................................................30 3.2.3 Finite Element Model........................................................................................34 3.2.4 Constitutive Models..........................................................................................35 3.2.5 Analysis Procedure...........................................................................................45 3.2.6 Simulation of Specimen 1: Concrete Column with Light Reinforcing.............45 3.2.6.1 Evaluation of Possible Failure due to Loading of PT ducts ...............52 3.2.6.2 Effect of Bond in Mild Reinforcing....................................................54 3.2.6.3 Precast Joint Modeling.......................................................................60 3.2.6.4 Shear Behavior....................................................................................61 3.2.7 Simulation of Specimen 2: Concrete Column with Heavy Reinforcing...........63 3.2.8 Simulation of Specimen 4: UHMWPE-ECC Column ......................................65 3.2.9 ECC Parameter Studies.....................................................................................69 3.2.10 Design Improvements for UBPT Concrete Column .........................................75 3.3 Summary .......................................................................................................................77 4 PREDICTION OF RESIDUAL DISPLACEMENTS......................................................81 4.1 Introduction...................................................................................................................81 4.2 Simulation of RC and UBPT Columns under Dynamic Loading.................................82 4.2.1 Background on Experiments.............................................................................82 4.2.2 Finite Element Model........................................................................................84