Development of a macro element for seismic SSI Analysis of shallow foundations

这项研究的目的是开发一种用于土-浅基础系统的宏观单元，该单元可以考虑近场土的非弹性行为和远场土的频率相关动力阻抗。该单元将极大地简化土-浅基础体系的建模方法，并将提高结构在地震激励下反应评估的准确性。土-结构相互作用(SSI)影响结构在地震作用下的反应已被公认，但由于地基-基础系统动力特性的复杂性，考虑SSI并不是一目了然的。在拟议的研究中，将开发一种单元，该单元可以捕捉近场土的非弹性行为以及远场土的频率相关动力学。这项开发将基于回转质量-弹簧-阻尼器组件和基于塑性的宏元件的集成。非弹性宏单元可以考虑多轴载荷(轴力、剪力和弯矩)的相互作用。回转质量-弹簧-阻尼器组合可以捕捉远场土体的频率相关动力响应。将这两个元素结合在一起，并针对典型的土壤类型和基础配置校准模型参数，将导致针对浅基础的计算效率高且足够准确的模型。建议的主要研究任务是：1)近场和远场土的两种建模方法的集成；2)针对复杂的有限元模型对非弹性宏观弹簧单元的集中模型参数进行校准；3)将所建立的模型与有限元分析进行对比验证；4)将该单元应用于典型的低层建筑结构和桥梁结构。使用计算效率高但精度高的数值单元将使工程师能够为结构系统开发优化设计，并准确评估结构在地震发生时的性能，这将导致一个具有韧性的社会抵御地震灾害。

The objective of the proposed research is to develop a macro element for a soil-shallow foundation system that can take into account the inelastic behaviour of near-field soil as well as the frequency-dependent dynamic impedance of far-field soil. The element will greatly simplify the modelling method for a soil-shallow foundation system and will increase the accuracy of the evaluation of structural responses under earthquake excitation. It has been well acknowledged that the soil-structure interaction (SSI) influences the response of a structure that is subjected to earthquake excitation, but the consideration of SSI is not straightforward due to the complexities in the dynamic behaviour of soil-foundation systems. In the proposed research, an element will be developed that can capture the inelastic behaviour of near-field soil as well as the frequency-dependent dynamic of far-field soil. The development will be based on the integration of gyromass-spring-damper assemblies and a plasticity-based macro element. The inelastic macro element can take into account the interaction of multi-axial loads (axial force, shear force, and moment). The gyromass-spring-damper assemblies can capture the frequency-dependent dynamic response of far-field soil. Integrating these two elements and calibrating model parameters for typical soil types and foundation configurations will lead to a computationally efficient yet sufficiently accurate model for shallow foundations. The proposed main research tasks are 1) integration of two modelling approaches for near- and far-field soil, 2) calibrating lumped model parameters for inelastic macro spring element against a sophisticated finite-element model, 3) verifying the developed model against finite element analyses, and 4) applying the element to a typical low-rise building structure and a bridge structure. The use of the computationally efficient yet accurate numerical element will allow engineers to develop an optimized design for a structural system and accurately evaluate the performance of a structure in the event of an earthquake, which will lead to a resilient society against seismic hazard.