An advanced assessment framework for seismic resilience of railway continuous girder bridge with multiple spans considering 72h golden rescue requirements

Abstract

Given the common sense that people in danger could survive with high probability in the golden rescue time of 72 h after earthquakes, railway bridges that are important transportation hubs and the lifelines for earthquake relief have been required to satisfy the necessities of safe passage and fast traffic for emergency response personnel in this critical period. To ensure the post-earthquake temporary functionality of the railway bridges to a sufficient safety level in golden rescue scenario, an advanced resilience assessment framework, including seismic resilience determinations for individual bridge components based on residual responses with respect to the plastic capacities originated from performance limit state definitions, definitions of three recovery levels considering repair efficiency for different recovery phases, and the series-parallel and parallel-serial system resilience models developed in temporal and spatial domains, was established. A commonly constructed irregular railway multi-span continuous girder bridge was chosen to verify the practicability of the aforementioned framework. The finite-element model of the illustrative bridge was developed taking abutment-girder interaction effects and nonlinear seismic behaviors of girder into account. Average spectral acceleration was taken as the intensity measure (IM) to consider the response variations originated from higher modes and natural period extension during earthquakes, and the site-matched and IM-based scaled ground records were adopted in the multiple stripe analysis to obtain instantaneous peak and residual seismic responses. Based on the framework, post-event resilience characteristics of bridge components were discussed, four recovery strategies were proposed for bridge system, and the seismic resilience of the illustrated bridge was assessed at system level. The research shows that the response contribution of fundamental dominant mode is only 64.37 %, indicating the dynamic response contributions from higher modes are considerable and the case bridge can show a strong irregularity during seismic events. Obvious nonlinear seismic behaviors occur to the superstructure where material strain in girder critical sections can increase to 0.00422 during earthquakes, which illustrates the inaccuracy of girder modeling only taking elastic behavior into consideration. Also, the prestress loss after earthquakes can reach 31.14 % and attention should be paid to the prestress recovery in subsequent repair works. Most components can satisfy the easy recovery resilience level, and the resilience is closely related to ground intensities and repair-waiting time; earthquake-induced functionality reduction can be 46.57 %, and resilience can increase by 25.35 % if the waiting time is shortened by 5 h. System resilience is influenced by the similar factors with component and varies in cases of different repair sequences due to the accumulation effect of repair-waiting time for various subsystems.