连续梁桥在主震-余震序列波下的地震易损性分析

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

地震通常以地震序列的形式发生,主震后通常会伴随余震。结构在主震中发生损伤后,即使较低震级的余震仍然会造成很强的结构破坏,并产生严重的后果。为了研究余震对于连续梁桥抗震性能的影响,本文采用易损性方法,以一座三跨连续梁为例,利用Open Sees程序建立三维有限元模型,选取并整合75条实测主震-余震序列波,分别在考虑余震及不考虑余震的情况下,使用云图法建立概率地震需求模型并计算其地震易损性,通过对比分析得到余震对结构地震易损性的影响。分析结果表明:余震会增大桥梁结构的地震需求及地震易损性,并且地震强度越大余震的影响也越大。因此忽视余震的影响往往会高估结构的抗震能力,在进行结构抗震设计时地震动输入应考虑主震-余震序列波。

Earthquakes are usually part of a sequence of ground motions, which can be defined as foreshocks, ma-inshocks, 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 contin-uous 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 in-crease significantly when the structure is subjected to a mainshock-aftershock sequence, and the effect of the after-shocks increase with an increase in seismic intensity. Therefore, neglecting aftershocks may cause considerable o-verestimation 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.