分层圆弧峡谷SV波地震差动模拟理论与桥梁破坏模式

为了探究局部地形及场地分层因素对地下多点地震动的影响,建立了分层圆弧峡谷模型,并进行了目标场地多点地震动模拟程序的开发和验证。在此基础上,对一跨越该场地的刚构桥进行了考虑多点激励作用下的地震反应分析。具体内容包括：首先,在推导得到SV波入射层状圆弧峡谷地震反应频域解基础上,依据规范谱确定矩阵的峡谷各位置自谱（绝对值）,联合自谱和峡谷相干函数得到互谱,进而与自谱共同构造出功率谱矩阵。由此同时体现了峡谷局部场地三大典型物理效应：散射、相干和分层效应,奠定了SV波入射下层状峡谷多点地震动模拟的基础,填补了由于竖向边界条件难以满足而大多受限于SH波入射理论解研究的空白。其次,基于上述结果,编制代码和可视化开发,实现理论方法程序化,并验证其可行性和可靠性。最后,为研究SV波输入下分层和峡谷效应多点激励对结构的影响,针对一峡谷桥梁进行模型建立、修正、多点地震反应计算以及分析比较。结果表明：①分层效应对结构反应影响明显,传统均匀介质的假定所带来的影响不容忽视;②采用传统适用于平整场地多点地震动作为激励,会导致与峡谷地形多点地震反应差别明显,且会低估结构反应;③SV波斜入射多点激励下所产生地震动的空间变异性,会使得地震反应计算结果幅值出现明显增大现象。该理论方法、程序开发可供类似工程场地分析参考。

Theory of SV-wave Multi-support Seismic Excitations by a Layered Circular-arc Canyon and Study on the Damage Mode of Bridge

In this study, the effects of local sites and layered media on underground multi-support seismic motions were investigated. A double-layered canyon was modeled, and a simulation program for multi-support seismic motions was developed and verified to simulate the target site conditions. Next, the seismic response analysis of a steel bridge crossing the target site was performed, considering underground multi-support seismic excitations. The details were as follows. First, based on the derived frequency-domain solution of the seismic response of a layered circular-arc canyon under SV-wave incidence, the auto-spectrum matrix (absolute value) was determined based on the standard spectrum, and the cross-spectrum could be determined by combining the auto-spectrum with the proposed canyon coherence function. The power spectrum matrix was derived by combining the auto-spectrum with the cross-spectrum, which reflected the three typical physical effects (scattering, coherence, and layered media) of the local site in the canyon and laid the foundation for simulating the multi-support ground motions of the layered circular-arc canyon. Subsequently, a theoretical method was developed by compiling the code and through visual development to verify the feasibility of the program and the reliability of the simulation results. Finally, the model of the bridge crossing a canyon was established and modified to reveal the influence of multi-support excitations of soil stratification and the canyon effect on a bridge subjected to SV-wave excitations. The multi-support earthquake response was determined, and the results were compared. The results indicate the following. ① The layered effect significantly influences the structural response, and the influence of the traditional homogeneous medium should be reasonably considered. ② The traditional multi-support seismic ground motions suitable for the flat site lead to considerable inaccuracies for the multi-support seismic response of a canyon terrain, and the structural response may be underestimated. ③ The spatial variability of ground motions generated by the oblique incidence of SV waves under multi-support excitations further increase the seismic response amplitudes of the bridge. The theoretical method and program development can be used as references for seismic response analyses of similar sites.