Seismic Fragility Assessment Of Bridge And Its Network Using Response Surface Models

In China,the current research in seismic hazards prediction of urban bridge networks is still inadequate,and so is the evaluation of seismic resistance and resilience ability of urban lifeline systems.In order to provide analytical methodology and strategic supports for bridge networks' seismic assessment,this study is intending to implement a quick assessment model of bridge network's seismic responses based on fragility analysis.The seismic hazards evaluation model is supposed to incorporate both detailed individual bridges and simplified bridge network evaluation as a whole.This paper focuses on the fragility analysis of multi-span simply supported curved concrete girder bridges(MSSS curved concrete girder bridges)based on Response Surface Models(RSMs).Specific contents are as follows:(1)The parametric modeling methodology is proposed for the group of MSSS curved concrete girder bridges based on OpenSees and Matlab.The moment curvature study and hysteretic study are carried out for pier columns.The relationships between earthquake input angles and seismic reponses of MSSS curved concrete girder bridges are investigated.The corresponding damage measures(DMs)and thresholds of different damage states are also identified based on the characteristics of bridge components.(2)The effects of bridges' size and material parameters on the seismic responses are investigated using Plackett-Burman Design.The RSMs are fitted and generated for each damage measure's mean value and standard deviation via Central Composite Design(CCD)and hundreds of NLTHAs.By the way,the RSM for first order eigenperiods is fitted using the same methods.The RSMs' fitting results are examined using the statistical software JMP.Finally,the fragility curves of pier columns and bearings are generated based on RSMs and the impacts of the five input parameters on the fragility curves are then compared and analyzed.(3)The first order reliability principle is utilized in this study to translate component level fragility curves to bridge level ones.The major transportation network of a certain county is separated from a map and two simplified bridge networks are extracted from it.The difference of the two simplified plots is based on that of two destinations.The network's fragility formulas are derived from basic series and parallel probability formulas and the fragility curves of the whole network are thus obtained.To exhibit an application of probabilistic fragility curves to deterministic decision making,the post-earthquake traffic capacity index are calculated and the traffic capacity states are distinguished for the selected bridge network.