非一致地震激励下飘浮体系斜拉桥易损性分析

Fragility Analysis of Floating Cablestayed Bridge Under Nonuniform Seismic Excitation

摘要:

利用OpenSees软件对一座主跨为420 m的斜拉桥建立有限元模型，分别进行了仅考虑失相干效应、考虑失相干效应和行波效应、考虑失相干效应和场地效应以及综合考虑失相干效应、行波效应和场地效应等4种非一致激励情况下的易损性分析.结合联合概率地震需求模型（TPSDM）和蒙特卡罗抽样获得了基于构件的体系易损性曲线.考虑地震动空间效应的飘浮体系斜拉桥损伤概率明显高于一致激励且失相干效应和场地效应的影响较为显著.失相干效应越明显，斜拉桥体系遭受地震损伤的概率越大.场地效应的影响较为复杂，总体上表现为相邻场地类型差异越大，沿地震波传播方向场地类型由软变硬时，体系损伤概率增加.行波效应对飘浮体系斜拉桥地震损伤的影响较小，易损性分析时忽略行波效应的影响不会造成较大的误差.因此，对飘浮体系斜拉桥进行非一致激励下的地震易损性分析应考虑失相干效应和场地效应的影响，目前广泛采用的一致激励下的易损性分析高估了体系的抗震性能.

关键词:飘浮体系斜拉桥;地震动空间效应;非一致地震激励;体系易损性

Abstract:

The finite element model of a cablestayed bridge with the main span of 420 m was built with OpenSees software. Fragility analysis was performed under four conditions considering incoherence effect only, incoherence and wavepassage effects, incoherence and siteresponse effects and spatial variation due to incoherence, wavepassage and siteresponse effects. System fragility curves were generated combining joint probabilistic seismic demand model (JPSDM) with Monte Carlo simulation based on component fragility. The system vulnerability of the cablestayed bridge under nonuniform excitation considering different sources of spatial variation effects is higher than that under uniform excitation. The effects of incoherence and siteresponse are obvious to the seismic response of the cablestayed bridge. With the increase of incoherence factor, the bridge as a system becomes more fragile. The siteresponse effect is more complicated, and the bridge tends to be more vulnerable if the soil types of nearby exciting locations become more different. The vulnerability of the cablestayed bridge increases when the soil type along the direction of propagation turns from relative soft to firm than the inverse condition. Neglecting wavepassage effect in fragility analysis would not cause an obvious error. Above all, incoherence and siteresponse effects should be considered in the fragility analysis of the floating cablestayed bridge under nonuniform excitation. The widely adopted fragility analysis under uniform excitation at the current time overestimates the aseismic behavior of the system.

Key words:floating cablestayed bridge; seismic spatially varying effect; nonuniform seismic excitation; system fragility