Probability-Based Performance And Post-Earthquake Functionality Assessment For Pile-Supported Bridges Under Combined Effects Of Scour And Earthquake Hazards

Scour and earthquake hazards should be considered in the design of cross-river bridges in earthquake-prone regions.Presently,scour and earthquake are treated as two independent hazards in the current worldwide design specifications for bridges.However,the scour has a detrimental and complicated effect on these cross-river bridges’ seismic input,response,and capacity.In this regard,the combined effect of scour and earthquake should be considered in the seismic design and/or seismic performance assessment for the bridge with scour potentials.In addition,acting as a critical joint in the traffic network,the bridge’s in-earthquake safety and post-earthquake load-carrying capacity are directly related to the traffic capacity of a transportation network.Presently,experience-based post-earthquake inspections and engineering judgment represent the main tools to estimate the remaining traffic capacity of a damaged bridge.However,a quantitative and scientific approach is still lacking to determine the bridge’s post-earthquake traffic functionality.More importantly,the bridge functionality loss is a crucial index for the seismic resilience assessment of a single bridge,a transport network,and a modern city.Therefore,this study aims to establish a quantitative relationship between the seismic damage states,post-earthquake vertical load-carrying capacity,and postearthquake traffic functionality for the crucial load-carrying components of the highway bridge,including bridge column,extended pile shafts,and pile group foundations,through numerical simulations and physical model tests.After that,this study proposes a probabilitybased seismic performance and post-earthquake functionality assessment approach for crossriver pile-supported highway bridges under the combined effects of scour and earthquake hazards.This study also represents a crucial step toward the seismic performance and resilience assessment,post-earthquake maintenance,and retrofits of highway bridges under scour and earthquake hazards.The main work and achievements of this study are as follows:Firstly,a probabilistic post-earthquake vertical load-carrying capacity degradation model for the bridge column is proposed.More specifically,this chapter establishes a series of finite element models(FEMs)of simplified single bridge columns,considering the uncertainty of structural parameters and ground motions.Then,the failure mode and post-earthquake loadcarrying capacity of the column with different earthquake-induced damage levels are investigated through incremental dynamic analysis(IDA)and pushdown analysis.Based on the numerical results,a probabilistic post-earthquake vertical load-carrying capacity degradation model for the bridge column is proposed.At the end of this chapter,the relationship between the column’s seismic damage state and its vertical load-carrying capacity loss is established.Secondly,a quasi-static test followed by a pushdown test on the extended pile shafts(EPS)in sandy soil is designed and performed in the laboratory.A general numerical approach for estimating the post-earthquake vertical load-carrying capacity of the EPS is developed,and a post-earthquake vertical load-carrying capacity degradation model for the EPS is proposed.In this chapter,more specifically,one extended pile-shaft specimen in homogeneous sand is designed and first subjected to lateral cyclic loads to simulate earthquake loads.A pushdown test is then performed on this laterally damaged specimen to determine its residual vertical load-carrying capacity.After that,a general numerical approach for estimating the postearthquake vertical load-carrying capacity of the EPS considering the soil-pile interaction is proposed and validated using the experimental data.Based on the validated numerical modeling approach,a series of FEMs for the EPS generated by a central composite design method is built in Open Sees.The hysteretic pushover analysis followed by pushdown analysis is then carried out on these EPSs to investigate their failure mechanisms and post-earthquake vertical load-carrying capacity.Based on the numerical results,a post-earthquake vertical load-carrying capacity degradation model and loss model for the EPS is proposed.In addition,a series of axial compression tests on short concrete columns with different confine materials are designed and performed in the laboratory to investigate the stress-strain constitutive model of the core concrete confined by materials with low elastic modulus,which provides a basis for the numerical simulation for the above test on EPS.Thirdly,a quasi-static test followed by a pushdown test on scoured pile group foundation in sandy soil is designed and performed in the laboratory.The seismic failure mechanism and ductile behavior of the scoured pile group foundation are investigated through experimental and numerical analyses.A post-earthquake vertical load-carrying capacity degradation model for the scoured pile group foundation is proposed.In this chapter,more specifically,a quasistatic test followed by a pushdown test on three scoured 2×3 pile group foundation specimens and a pushdown test on one scoured 2×2 pile group foundation specimen are designed and carried out in the laboratory.Based on the experimental data,the seismic failure mechanism of the scoured pile group foundation is investigated,and a post-earthquake vertical loadcarrying capacity degradation model for the scoured pile group foundation is proposed.In addition,this study proposes an efficient FEM for pile groups based on a beam on the nonlinear Winkler foundation(BNWF)approach.This FEM uses asymmetric lateral soil springs(or p-multipliers)to describe the difference in soil resistance exerted on leading and trailing piles when cyclic lateral loads are applied.The proposed FEM is validated through a comparison of the numerical response with the experimental measurements.After that,a series of FEMs for pile group foundation cases generated by a central composite design method is built in Open Sees using the validated modeling approach,and a comprehensive parametric analysis is performed to investigate the ductile performance of scoured pile group foundations and to identify the high sensitivity parameters through tornado diagram method.At the end of this chapter,the seismic damage state of the scoured pile group foundation is related to its post-earthquake vertical load-carrying capacity loss.Fourthly,this study proposes a probability-based seismic performance assessment and post-earthquake functionality assessment approach for pile-supported bridges under the combined effects of scour and earthquake hazards.More specifically,this chapter proposes a framework for the seismic performance assessment and post-earthquake functionality assessment.The relationship between the seismic damage state,post-earthquake vertical loadcarrying capacity,and the traffic capacity for the single bridge column,extended pile shafts,and pile group foundations is established.After that,this chapter emphatically introduces how to establish the coupled soil-foundation-bridge model with scour effects and soil-pile interaction,how to perform the seismic performance assessment for the scoured pilesupported bridges using seismic fragility,and how to develop the traffic capacity fragility curve and perform the post-earthquake traffic functionality assessment.At the end of this chapter,two typical examples are used to achieve the post-earthquake functionality assessment for pile-supported bridges...