断层走向对刚构桥地震反应的影响

我国西部部分连续刚构桥临近地震断层建设，在抗震分析时通常会忽略断层走向与桥梁纵桥向夹角对其地震反应的影响。利用Midas Civil软件建立4座墩高不同的大跨度连续刚构桥模型，选取10组近断层强震记录进行时程分析，研究断层走向对刚构桥地震反应(位移和弯矩反应)的影响。结果显示：在水平双向近断层地震动输入下，桥梁主墩及主梁纵桥向地震反应在断层走向与纵桥向夹角为75°～135°范围内最大，而横桥向最大地震反应则发生在夹角为0°～30°或120°～180°范围；在三向近断层地震动输入下，与仅考虑水平双向地震动输入下的桥梁地震反应相比，竖向地震动对主梁竖向弯矩响应的影响较大，特别是主墩和主梁的交界处，增大比例可达2倍及以上。就文章选取的4座桥梁算例，不考虑断层走向和桥梁纵桥向的夹角则存在低估桥梁地震反应的可能，低估误差在15%～40%左右。

Influence of fault strike on the seismic response of rigid frame bridges

Some continuous rigid frame bridges are constructed adjacent to active faults in western China, but the influence of the angle between the fault strike and the longitudinal bridge direction on the seismic response of rigid frame bridges is usually ignored in the seismic design. Four long span continuous rigid frame bridge models with different pier heights were established by Midas Civil software in this paper. Ten groups of near fault ground motions were selected for time history analysis to study the influence of the fault strike on seismic responses of the displacement and ending moments in rigid frame bridges. Results show that under horizontal bidirectional near fault ground motions, the longitudinal seismic response of main piers and main girders is the largest when the angle between the fault strike and the longitudinal bridge direction varies from 75° to 135°, while the maximum transverse seismic response occurs when the angle is in the ranges 0°-30° or 120°-180°. Compared with the seismic response of bridges under horizontal bidirectional ground motions, the vertical ground motion has a great influence on the vertical bending moment response of the main girder under three directional near fault ground motions. Specifically, the seismic response can be multiplied two or more times, especially at the junction of the main pier and the main girder of the rigid frame bridge. It is possible to underestimate the seismic response of the four bridges selected in this paper if analyzed without considering the angle between the fault strike and the longitudinal bridge direction; the underestimated error is about 15%-40%.