Development of a frequency- and amplitute-dependent macro element for seismic SSI analysis of shallow and deep foundations

提出的研究目标是开发一种计算效率高的数值单元，该单元可以捕获地震土-结构-相互作用分析中浅层和深层基础的非弹性和频率依赖性。对地基系统进行明确建模的挑战之一是系统在动力荷载作用下的复杂响应。实际上，地基系统是一个具有非弹性材料的大的半无限连续体。土与基础界面的非线性（即摇晃和滑动）也会影响基础的滞回特性。此外，地基系统的动力响应是频率相关的。根据地基和结构体系的相对阻抗，非弹性特性和频率相关特性都需要用数值模型来表示。然而，在简化的模型中，例如集总或温克勒弹簧模型，很难捕捉到这些特征。在提出的研究中，将发展一个广义的宏观单元，用它可以模拟近场土壤的非弹性行为和地基系统的频率依赖特征。PI和行业合作伙伴开发了一个框架，其中宏元素可以与递归参数模型集成。宏观单元基于塑性理论，捕捉近场土的非弹性，而递推参数模型捕捉频率相关特征。该框架应用于二维浅基础。在本文提出的研究中，该框架将被普遍化，使其可以应用于二维和三维问题的浅基础和深基础。该元件将根据现有的实验测试结果和复杂的有限元分析进行校准和验证。该单元将减少建模工作量和计算时间，同时为结构抗震评估提供实际准确的地基系统响应。该元素的发展将导致安全和优化的建筑和桥梁结构。****

The objective of the proposed research is to develop a computationally efficient numerical element which can capture both the inelasticity and the frequency dependency of shallow and deep foundations for seismic soil-structure-interaction analyses. One of the challenges in explicitly modelling a soil-foundation system is the complexity of the system's response under dynamic load. In reality a soil-foundation system is a large semi-infinite continuum with inelastic material. The nonlinearity at the interface between the soil and the foundation (i.e. rocking and sliding) also influences the hysteretic behaviour of the foundation. In addition, the dynamic response of the soil-foundation system is frequency dependent. Depending on the relative impedance of the soil-foundation and the structural system, both the inelasticity and the frequency dependent characteristics need to be represented in a numerical model. In a simplified models, such as lumped or Winkler spring models, however, it is difficult to capture these characteristics. In the proposed research, a generalized macro element will be developed with which the inelastic behavior of near-field soil and the frequency dependent characteristics of the soil-foundation system can be modelled. The PI and the industry partner has developed a framework in which a macro element can be integrated with a recursive parameter model. The macro element is based on a plasticity theory and captures the inelasticity of near field soil while the recursive parameter model captures the frequency dependent characteristics. The framework was applied to a two-dimensional shallow foundation. In this proposed research, the framework will be generalized such that it can be applied to both shallow and deep foundation for both two- and three-dimensional problems. The element will be calibrated and validated against available experimental test results and sophisticated finite element analyses. The element will reduce the modelling efforts and computational time while providing practically accurate response of soil-foundation system for seismic assessment of structures. The development of the element will lead to safe and optimized buildings and bridge structures.****