A Novel Method Coupling Numerical And Analytical Methods For Seismic Dynamic Response Analysis Of Soil-structure Interaction Systems

A novel coupling method for performing nonlinear seismic analysis of soil-structure interaction (SSI) systems is presented, combing analytical and numerical methods. The closed form analytic solutions in frequency domain for SSI problems has limitations that it can be applicable to only simple linear elastic structure, rigid foundation and semi-infinit linear elastic soils. On the other hand, nonlinear finite element method is able to simulate the nonlinear seismic response of SSI systems, dealing well with nonlinear SSI. However it is time consuming, and need to treat the special boundary of soil domain. In this context, the thesis presents a new coupling method for nonlinear seismic analysis of SSI problems. This method is based on substructure method, in which the structure is modeled ans analyzed by nonlinear FEM, and the soil by a time domain solution transformed from frequency domain closed form solution using a discrete time domain recursive filter. The boundary conditions of force and displacement between soil and structure are satisfied by using Newton’s method. The nonlinear structural behavior is modeled by a FEM software, OpenSees, and closed form analytical solutions is implemented in C++programming. The coupling between this two substructures are beased on a real-time data communication technique, the CS integration technique.Several examples are studied in order to verify the coupling methods in sense of efficiency, precision and practicability. First of all, a single degree of freedom (SDOF) structure and soil system is taken as an example. The basic steps and key points of SSI analysis are presented in detail. The displacement frequency response function obtained by coupling method is computed with the corresponding analytical solution in frequency domain. The numerical error is calculated and the possible source is analyzed. The effect of time step size and damping on the precision of the coupling method is discussed. The change of the structural responses and displacement frequency responses with increasing nonlinearity of the SSI system is studied. Secondly, the coupling method is applied to a simple MDOF structure and soil system to verify its precision, stability and applicability to MDOF structure-soil systems. The analytical frequency response function of the SSI system is derived, which is then used to verify the corresponding function obtained by the coupling method. For responses of SSI system with nonlinear MDOF structure, the effect of time step size, damping, and earthquake intensity are studied. The difference of the nonlinear structural responses with SSI v.s. without SSI is studied. Finally, the coupling method is used for seisimic analhysis of a real SSI system, the Millikan library in university of California institute of technology. The nonlinear seismic responses are studied. The differences are studied between conditions of considering SSI v.s. not considering SSI effects. This paper proposed a practical method for nonlinear seismic analysis of SSI systems, and part of the research results provides valuable insight for engineering practice.