Use of response surface metamodels to generate system level fragilities for existing curved steel bridges

Fragility curves that have been developed for curved steel bridges have not extensively addressed horizontal curvature and do not sufficiently account for major contributing curved bridge components that influence their seismic response (e.g., radius of curvature, cross-frame spacing, etc.). This study considers a group of horizontally curved steel I-girder bridges located in Pennsylvania, New York and Maryland to examine the influence of important parameters on their seismic response and develop system level fragility curves for the bridge group. The developed methodology is then applied to specific bridges. This paper provides description of the procedure used to generate representative curved bridge fragility curves using input from select component fragilities. The curves were generated for representative bridge systems, and utilized fragilities from important bridge seismic components created using Response Surface Metamodels (RSMs). The critical components included items at the bearings and the supporting pier columns. A statistical screening approach, using design of experiments and incorporating seismic response information obtained from nonlinear time history analyses, was used to determine critical curved bridge component seismic response ranges. Monte Carlo simulation was then implemented to assist with fragility generation for both the group of bridges and sample bridges. Using the generated fragility, case studies were performed to investigate the effects of the certain bridge parameters on seismic vulnerability. Findings indicated that parameters that significantly influenced seismic fragilities were the number of spans, radius of curvature, and maximum span length.