跨越Ⅴ形峡谷桥梁多层介质效应的多点激励破坏模式

Failure Mode of Bridges Under Multi-support Excitation in a Ⅴ-shaped Canyon with Multi-layer Topography

由于崎岖地形(非平坦地表和非均匀地层)具有复杂的地震动空间变异性,对于该类场地效应的地震特异性所引发的结构差动损害尚无系统性的研究。为了深入研究崎岖地形下地震动空间效应对结构的影响,针对多层非均匀介质Ⅴ形峡谷这种特殊地形,详细分析了Ⅴ形场地下地震动频谱特性的影响因素(行波效应、相干效应和局部场地效应等),并模拟了相应的地震动输入;对一横跨Ⅴ形峡谷的连续钢箱梁桥进行了有限元计算,对比分析了不同地震动输入和不同边界条件下结构模型的地震响应;探究了Ⅴ形场地超大震作用下的桥梁破坏模式,计算出结构的薄弱部位,并着重对比了Ⅴ形峡谷场地和平坦场地2种地形下的地震激励对结构破坏模式的影响差异,揭示了Ⅴ形峡谷场地下的模拟多点地震输入特异性对桥梁的结构响应和破坏模式的特殊影响,发现同水平场地相比该类场地下的地震激励会在桥梁内部引发额外的差动内力,进而使桥梁破坏更早发生并改变了结构的破坏模式。结果表明:①Ⅴ形峡谷场地极大地改变了地震波场中的散射波组成,且同水平场地地震激励相比,其对结构具有更强的空间差动效应,从而引发更大的差动内力;②与水平场地相比,Ⅴ形峡谷场地地震动输入下的桥梁破坏发生时间较为提前,且初始破坏点并不相同,从而导致结构的破坏模式改变。

Rough terrain(i.e.,a non-flat surface with an inhomogeneous foundation)has a naturally strong earthquake spatial variability.No specific systematic study has yet been conducted on structure differential damage caused by topographical seismic specificity.To study further the seismic underground spatial effect on structures in rough terrain,this study investigated the influence factors on seismic spectral characteristics(effects of travelling wave,coherency,and local site)in aⅤ-shaped canyon with multi-layer inhomogeneous media,and simulated the corresponding seismic inputs.A continuous steel box-girder bridge over aⅤ-shaped canyon was analyzed using finite element method,and the bridge responses under different seismic inputs and different boundary conditions were compared.The bridge failure mode and weak part under a mega earthquake were investigated.Comparison between the failure modes of bridges inⅤ-shaped-canyon and flat topographies was conducted to reveal the specific effects on bridge response and failure mode in aⅤ-shaped canyon topography.Compared with the flat terrain seismic response,the results show that excitation leads to additional internal differential force on the bridge,thereby advancing the bridge failure and changing the failure mode.Numerical results show that theⅤ-shaped site greatly changes the components of scattering seismic waves,enhancing the differential effect of structural vibration as compared with the flat terrain.Compared to the flat terrain site,bridge damage in aⅤ-shaped canyon occurs earlier and the initial failure point varies,thus changing the bridge failure mode.The topography has a great effect on the seismic response of a bridge spanning aⅤ-shaped canyon.The relevant conclusions can be used as a reference for seismic engineering analysis in similar fields of study.