水域地下三维相干多点地震动模拟理论与方法

Those structures such as bridges across sea and sub-seabed tunnels are usually characterized by the large span, long distance, curved layout, existing form of being buried in seabed, and have the features of that the modal frequencies in vertical direction are close to those in the other horizontal direction even distinctly smaller than those of common structures. Reliable seismic analysis results of those structures are logically required to obtain reasonable multi-support earthquake motions. Currently, relevant theoretical studies are usually confined to simulate one or two dimensional spatially-varying earthquake ground motions in horizontal directions. However, the objective influence factors including the coherence between vertical and each horizontal earthquake motions, soil moisture content and boundary conditions between seabed surface and overlying water are not considered in the current theoretical studies to simulate multi-support seismic excitations. Therefore, this project application is being submitted for approval and its main contents are given here. Firstly, for underground multi-layer soil overlying water, taking soil moisture content into account and deriving the corresponding transfer function. Then, establishing underground power spectrum of multi-layer soil overlying water. Meanwhile, constructing an uniform expression that can simultaneously describe 3D multi-support cross-coherence between vertical and two horizontal dimensions. Furthermore, determining boundary conditions for the interface between seabed surface and overlying water and soluting the transmission and reflection coefficients of the interface, and then incorporating the coefficients into the target power spectrum and cross power spectrum. Finally, forming 4D power spectrum matrix to simulate 3D multi-support earthquake underground motions in water area and developing visual program. The project belongs to a fundamental theoretical study, which aims at providing necessary theoretical evidence to simulate 3D multi-support earthquake underground excitations in water area and further meeting engineering requirements.

跨海桥梁或隧道等工程具有跨度大、距离长、线型曲、竖向自振频率低甚至与水平向频率相当等特点，其地震分析结果的可靠性依赖于输入多点地震动的合理性。传统适用于陆表结构的水平一维或二维相干多点地震动模拟方法，由于未考虑竖向与水平两维度的相干性、水域地下土含水率以及海床与水交界面效应等客观因素，难以充分满足现实需求。为此，需要开展水域地下三维相干多点地震动的模拟方法。首先，推导考虑双相介质效应地基土层传递函数，建立水域地下地震动目标功率谱模型，构建竖向与水平两向的三维相干函数模型；然后，定性确定海床与海水交界面的边界条件，定量求解地震动在土-水交界面的透射和反射系数，并将此系数引入至自谱和互谱中；最后，构造模拟水域地下三维空间相干的多点地震动的四维矩阵，由此形成理论方法并进行程序开发。申请项目为基础性研究，旨在为水域地下三维相干多点地震动输入提供切实有效的理论依据和方法，更好地服务于工程实际。

基于场地特征的多点地震动模拟是结构进行可靠的地震安全评估的前提。水域场地具有双相介质属性，随着滨海地区大量长大结构工程的修建，适用于单相介质的地震动模拟方法已无法充分满足工程实际需求。同时，长大结构工程通常具有纵向跨度大，基础埋置深以及所处地形复杂等特点（如港珠澳跨海大桥），为获得更加精确的地震反应，输入地下支撑点处的多点相关地震动输入是关键。为此，本项目充分关切这一科学问题，对水域场地地下多点地震动模拟方法展开了研究。首先，推导并得到了考虑双相介质效应地基土层的传递函数，并将有上覆水层时土水交界面效应纳入推导过程中，提出并实现了水域环境多点地下地震动模拟方法并开发了可视化程序。其次，针对第二类分层峡谷地形场地，开展了适用于U形，圆弧形和V形峡谷的理论研究，开发了考虑局部地形效应的地下多点地震动程序。最后，明确给出了第二类分层峡谷地形桥梁在多个维度下地震作用过程中的破坏模式差异及其物理成因。本项目提出方法和相关研究具有理论研究和指导工程实际应用意义，可为相关工程项目提供参考。

内容获取失败，请点击重试