多跨连续钢梁桥的时变地震易损性研究

TIME-DEPENDENT SEISMIC FRAGILITY ANALYSIS OF MULTI-SPAN CONTINUOUS HIGHWAY BRIDGES

针对以往建立易损性曲线过程中通常忽略结构多构件老化与退化对地震响应的潜在影响这一情况,本文对考虑多构件退化的桥梁时变地震易损性进行了研究。该方法主要研究钢筋混凝土桥梁暴露于劣化环境下的地震性能,分析了除冰盐中氯化物引起的钢筋混凝土圆柱和桥梁支座多构件腐蚀退化机理,着重考虑氧化产物导致混凝土保护层开裂下的混凝土退化与氯腐蚀导致的钢筋退化,桥梁多构件退化下的地震响应可通过三维非线性动力分析获得。此外,在建立时变易损性曲线过程中,基于蒙特卡洛仿真方法,综合考虑了氯离子扩散过程、地面运动以及材料参数的不确定性。对遭受氯化物侵蚀的某一多跨连续(MSC)钢梁桥进行非线性动力分析,数值结果表明,地震作用下若考虑时变腐蚀退化,桥梁构件和系统易损性曲线均会随着时间推移而发生相应的改变,失效概率增大;与单构件腐蚀退化的时变地震易损性曲线相比,考虑多构件退化的桥梁系统时变易损性更加保守,利于工程安全。对桥梁结构进行抗震性能评估时,以上结果验证了地震灾害和环境危害相结合的重要性。

This paper presents a methodology to develop a time-dependent seismic fragility for highway bridges, which considers the potential effects of degradation and aging of multi-components on seismic responses traditionally neglected in fragility modeling. The study investigates the seismic performance of reinforced concrete bridges exposed to aggressive environments and evaluates the deterioration mechanism of reinforced concrete columns and bearings exposure to chlorides-induced corrosion from deicing salts, as well as considers the degradation of both concrete and steel under oxide-induced cracking of concrete cover. The members’ degradation characteristic and their seismic responses are obtained by nonlinear dynamic analysis. Furthermore, the randomness involved in diffusion process of chloride ions, as well as the variation of material in bridge and the uncertainty of ground motion, are taken into account in probabilistic terms. The proposed procedure is applied to a multi-span continuous (MSC) steel girder bridge exposed to corrosion. The case study subjected to earthquakes is then performed by nonlinear dynamic analysis. The results indicate the potential evolving for fragility curves of component and system under seismic loading considering time-variant corrosion-induced degradation. The results also show that bridge’s components suffer a substantial increase in seismic vulnerability owing to corrosion and the use of multi-components’ aging can get some more conservative results, which will be more conductive to the safety of structures, relative to the results based on the deterioration of individual component. The proposed evaluation approach has confirmed the importance of an appropriate combination of earthquake and environmental hazards in the evaluation of the lifetime seismic performance of bridges.