跨倾滑正断层桥梁地震响应数值模拟

为揭示跨倾滑正断层桥梁的地震响应规律，以海文大桥跨断层引桥为研究对象，根据地震震级和断层参数间的关系构建了铺前-清澜断层的物理模型，并基于空间随机场模型生成该断层滑动的空间非均匀分布；采用基于断层破裂物理过程的地震动混合模拟方法生成断层两侧可能发生的最大永久位移地震动；同时，采用OpenSees建立了全桥三维动力有限元模型，分析了永久位移地震动频带、桥梁与断层相对位置、竖向地震动及减隔震方法对该桥地震响应的影响规律。研究结果表明：所采用的地震动模拟方法可以合理考虑断层断裂的复杂性，生成地震动的反应谱在短周期段和设计反应谱吻合良好，在长周期段具有显著的滑冲效应特征，可有效模拟断层两侧的永久位移地震动;在跨断层桥梁地震响应分析方面，断层错位和高频带地震动对跨断层桥梁地震响应均有较大的贡献，跨断层桥梁地震响应分析须采用具有永久位移的宽频带地震动作为地震动输入，仅采用高频带地震动或者采用断层错位进行静力分析均会低估桥墩的地震响应；而位于断层同侧的桥梁主要受高频地震动的影响，跨断层桥梁的地震响应远大于断层同侧桥梁的响应；不考虑竖向地震动会低估跨倾滑断层桥梁纵桥向的地震响应，且跨径越小竖向地震动的影响越大，在进行跨倾滑断层桥梁抗震设计时，应选取较大跨径的简支梁桥来减轻竖向地震动的影响。同时，合理的限位拉索设计可利用桥墩的抗震能力明显改善跨断层桥梁的支座变形，减小因断层错位引起的桥梁损伤。

Numerical analysis on seismic response of bridges crossing normal fault rupture zone

In order to explore seismic responses of bridges crossing normal fault rupture zone, the fault crossing approach of Haiwen bridge was taken as a case study. The fault model of the Puqian-Qinglan fault was developed based on the relationship between earthquake magnitude and fault parameters. Spatial non-uniform slip distributions were generated using random field model. Ground motions with permanent ground displacement were synthesized using a hybrid simulation method based on the physical process of fault rupture. Meanwhile, a 3D dynamic finite element model of the bridge was established using OpenSees to analyze the influences of frequency bands, the relative position of the bridge and fault, the vertical ground motion and the methods of isolation on seismic responses of the bridge. The results show that the ground-motion simulation method adopted in this paper can be utilized to consider the complexity of the fault rupture reasonably. The response spectra of synthetic ground motions agree well with the design spectra in the short period, and have a significant fling-step effect at the long period. It is an effective tool to simulate the ground motions with permanent ground displacement adjacent both sides of the fault.Both fault offset and high-frequency ground motions have great contribution to the seismic response of fault crossing bridge. Broadband ground motions with permanent ground displacement should be used as ground motion inputs for the seismic response analysis of fault crossing bridge. Only using high-frequency ground motions or fault dislocations will underestimate the seismic response of the bridge. The bridges on the same side of the fault are mainly affected by high-frequency ground motions. Seismic responses of the fault crossing bridge are much larger than those of the bridges on the same side of the fault. The longitudinal responses of the fault crossing bridge will be underestimated without considering vertical ground motions. The influence of vertical ground motions increases with the decrease of the bridge span. Larger span is recommended mitigating the influence of vertical ground motions for the seismic design of fault crossing bridges. Meanwhile, a reasonable restrainer design can reduce the deformation of bearings by utilizing the seismic capacity of bridge piers, so it can reduce the damage of the bridge that introduced by fault offset.