Seismic fragility analysis of a continuous girder bridge subject to an earthquake mainshock-aftershock sequence

Earthquakes are usually part of a sequence of ground motions, which can be defined as foreshocks, mainshocks, and aftershocks. A large mainshock may trigger numerous strong aftershocks. During earthquake events, aftershocks have the potential to cause severe damage to structures when damage already exists from the mainshock. Using seismic fragility analysis, this paper analyzes the effect of aftershocks on the seismic performance of a continuous girder bridge. For the case study, a three-dimensional finite element model of a three-span continuous girder bridge was established using OpenSees, and 75 recorded mainshock-aftershock seismic sequences were selected and integrated into the process. The probabilistic seismic demand model was established by the cloud method under two conditions: taking seismic sequences into account and not taking them into account. Then comparisons were made to investigate the influence of aftershocks. It was found that the seismic demand and seismic fragility of the bridge increase significantly when the structure is subjected to a mainshock-aftershock sequence, and the effect of the aftershocks increase with an increase in seismic intensity. Therefore, neglecting aftershocks may cause considerable overestimation of the seismic performance of the bridge. Thus, seismic mainshock-aftershock sequences should be considered for seismic dynamic input in the seismic design of engineering structures. © 2016, Editorial Department of Journal of HEU. All right reserved.