地震动入射角对空心薄壁高墩桥梁地震易损性的影响

Impact of ground motion incident angles on seismic vulnerability for bridge with thin-walled hollow tall pier

为了充分评估空心薄壁高墩大跨桥梁结构的抗震性能,以中国西部某四跨高墩刚构-连续组合体系桥梁作为研究对象,基于三维地震易损性分析方法,计入竖向地震动的影响,结合现行桥梁抗震设计规范,采用增量动力分析方法讨论了水平地震动入射角对桥梁构件地震易损性的影响;依据一阶可靠度理论分析了地震动入射角对桥梁结构系统易损性的影响规律。研究结果表明:2#、3#刚构桥墩的弯曲和剪切易损性云图与1#、4#悬臂墩的弯曲和剪切易损性云图差异明显,桥墩弯曲和剪切的地震易损性不仅与地震动入射角有关,还与桥墩结构形式有关;支座在轻微损伤、中度损伤、重度损伤及完全损伤状态下的损伤概率分布相似,地面峰值加速度为0.4g时,最大损伤概率的地震动入射角为0°和180°,当地面峰值加速度大于0.6g时,轻微损伤和中度损伤的最不利入射角为0~180°,支座变形的最不利地震动输入方向主要为纵桥向和横桥向。由此可见,各关键构件的不同损伤指标下的损伤概率随地震强度、方向变化的规律各不相同;不同损伤指标下系统及各构件的最不利地震动入射角及其区间数量和范围也各不相同;仅讨论纵桥向或横桥向构件地震易损性不能合理评估桥梁结构的实际抗震需求,采用三维地震易损性分析方法能准确定位最不利地震动入射角,实现高墩大跨桥梁结构抗震性能的准确评估。

A certain 4-span rigid-frame-continuous composite bridge with tall piers in western China was considered as the research object to fully assess the seismic resistance performance of long-span bridge structures with thin-walled hollow tall piers. Combined with the current bridge seismic design code, the incremental dynamic analysis method was adopted to discuss the impact of horizontal ground motion incident angle on the seismic vulnerability of bridge components based on the three-dimensional seismic vulnerability analysis method, and the influence of vertical ground motion was considered. The impact law of ground motion incident angle on the seismic vulnerability of bridge structural system was analyzed in considering the first-order reliability theory. Analysis result indicates that the bending and shearing vulnerability nephograms of the 2~# and 3~# rigid-frame piers differ significantly from the corresponding nephograms of the 1~# and 4~# cantilever piers. The bending and shearing seismic vulnerabilities of pier are not only related to the ground motion incident angle but also to the pier structural type. The distributions for the damage probability of bearings with slight, moderate, severe, and complete damage states are similar. The ground motion incident angles for the maximum damage probability are 0 and 180° when the peak ground acceleration is 0.4g. The most unfavorable incident angles for the slight and moderate damage states are 0-180° as the peak ground acceleration increases over 0.6g. The most unfavorable ground motion incident directions for the bearing deformation are mainly the longitudinal and lateral directions of the bridge. It can be seen that the damage probabilities for various damage indices of the various key components differ along with the various intensities and directions for ground motions. The number and ranges for the most unfavorable ground motion incident angles and their relative intervals of the structural system and its components with various damage indices also differ. The seismic demand for the bridge structure can not be properly evaluated by only discussing the seismic vulnerability in the longitudinal and lateral directions of the bridge. The most unfavorable ground motion incident angle and even the seismic resistance performance of long-span bridges with tall piers can be located and evaluated accurately using the proposed three-dimensional seismic vulnerability analysis method. 3 tabs, 13 figs, 32 refs.