近断层地震下连续梁桥随机振动与易损性分析

Random vibration and seismic fragility analysis of continuous girderbridges under near-fault ground motions

由于桥梁建设场地难免会靠近地震活动断层,为了评定近断层地震动作用下连续梁桥的地震安全性水平以及提高抗震性能,亟待发展连续梁桥非线性随机地震动力响应与易损性分析的统一、准确方法。考虑到近断层地震动是典型的随机过程激励,本文提出了基于直接概率积分法的连续梁桥结构非线性随机振动响应与地震易损性准确、通用分析的新框架。发展直接概率积分法,准确高效地计算连续梁桥结构的随机振动响应;结合连续梁桥多种失效状态,根据动力可靠度的首次超越破坏准则,利用直接概率积分法对连续梁桥进行了地震易损性分析。最后,展示了近断层随机地震动激励作用下四跨非线性连续梁桥算例结果,验证了直接概率积分法的准确性特点。比较了近断层脉冲型和无脉冲地震动对非线性连续梁桥地震易损性曲线的影响。结果表明:近断层地震动的速度脉冲显著加剧了连续梁桥结构受到的地震破坏,增大了桥梁结构进入不同破坏状态的超越概率。

The construction sites of bridges are sometimes located near active seismic faults.Thus,there is an urgent need to develop a unified and accurate method for nonlinear stochastic dynamic responses and seismic fragility analyses to evaluate the seismic safety levels of continuous girder bridge structures under near-fault ground motions and to improve their seismic performance.Considering the near-fault ground motions as a kind of typical stochastic process excitation,this paper proposes a new accurate and versatile framework based on the direct probability integral method(DPIM)for analyzing nonlinear random vibration responses and seismic fragilities of continuous girder bridges.Here,the DPIM is developed to accurately and efficiently calculate the random vibration responses of a nonlinear continuous girder bridge.Then,by considering several damage states of the girder bridge system and referring to the first-passage failure criterion of dynamic reliability,the seismic fragilities of nonlinear continuous girder bridges are analyzed via DPIM.Finally,the numerical results of a four-span nonlinear continuous girder bridge under near-fault stochastic ground motions are displayed,thus verifying the accuracy of DPIM.In addition,the effects of near-fault pulse-like and nonpulse ground motions on the seismic fragility curves of the nonlinear continuous girder bridge are compared.The results indicate that the velocity pulses of near-fault ground motions cause more damage to the continuous girder bridge structures,thus increasing the exceedance probability of bridge structures entering different damage states.