Adjustment Factors for Seismic Fragility Characteristics of High-Speed Railway PSC Box-Girder Bridges with Different Span Numbers
Seismic resilience assessment of railway networks requires fragility functions for all bridges in the network. However, developing detailed probabilistic models and conducting nonlinear time-history analyses for each bridge configuration requires substantial computational effort. To overcome this limitation, this study proposes adjustment factors for system-level seismic fragility curves for prestressed concrete box-girder bridges, the most common class of high-speed railway bridges in Korea, with different numbers of spans. A database was constructed from design documents of 69 bridges in the first phase of the Honam High-Speed Railway, and major uncertain model parameters were identified. Three-dimensional probabilistic track-bridge models were generated using Latin hypercube sampling, and nonlinear time-history analyses were performed for 2-, 3-, 4-, 5-, 10-, and 20-span bridge models. Component fragility curves were derived using probabilistic seismic demand and limit-state models, and system fragility curves were obtained under a series-system assumption. Bearing responses dominated the slight-limit-state system fragility, followed by column responses. As the number of spans increased from 2 to 20, the median value of the fragility curve decreased by approximately 67%. Finally, adjustment factors for the median value and dispersion of the fragility curve were proposed to estimate the seismic vulnerability of bridges with different numbers of spans without additional computational effort.