Dynamic Substructure Method For Soil-Multistory Buildings Interaction System

Multi-story building is gradually adopted since it has advantages such as saving land and making efficient use of architectural space. As our country is sited at earthquake-prone area, seismic analysis of multi-story building has been paid much more attention. Structural earthquake damage is closely related to ground condition, so it's necessary to introduce the effect of soil-structure interaction. However, high cost of calculation, complicated analysis process, difficulties of engineering application are key problems while coping with the problem. Therefore, searching for efficient and convenient methods has theoretical significance and engineering value. Response to the above problems, this thesis has done some research. The following innovative work and achievements are included:(1) Constrained mode synthesis (CMS) method is discussed and applied to a soil-multistory building interaction system. Method of forming the damping matrix by CMS method in a non-proportional damped system is presented, and the reduction method of degree of freedom (DOF) on the interface is also introduced. Result shows that the method is completely applicable for modal analysis and elastic time history analysis of soil-multistory building interaction system.(2) Based on constrained mode synthesis method, a linear space consists of displacement vectors calculated by different mode cut-off numbers is defined. A function is also defined and verified to be a norm of this linear space mathematically. Then adopt the maximum value of that norm as the potential energy criterion. The relationship between potential energy criterion and mode cut-off number is derived. Consequently, the mode cut-off criterion based on potential energy criterion is proposed. It provides convenience for using constrained mode synthesis method.(3) Based on the characteristic that structures exist local plastic regions, the mixed linear-nonlinear CMS method was presented. The basic idea is to define the component which is hard to get into nonlinear stage in the system as linear substructure while others as nonlinear substructure. DOF of linear substructures is reduced and will synthesized with nonlinear substructures, subsequently solve the mixed equation and obtain the dynamic response. In addition, result of nonlinear seismic response analysis of 2-dimensional soil-multistory buildings interaction system shows that the proposed method is effective and accurate.(4) Expand the mixed linear-nonlinear CMS method to dynamic analysis of 3-dimensional model. For 3-dimensional dynamic analysis, the way of using the mixed linear-nonlinear CMS method is discussed when non-linear substructure is coupled with several linear substructures. Furthermore, the proposed method is used to solve the 3-dimensional soil-multistory buildings interaction system dynamic problem and several dynamic analysis has been carried out according to two kinds of soil boundary conditions by different seismic excitations. The results indicate that the proposed method is accurate and effective. In addition, the nonlinear soil region scale is studied by several numerical experiments. The results show that this method could be more effective when more experience is involved.(5) To introduce the effect of nonlinear soil-structure interaction easily, based on the mixed linear-nonlinear constrained mode synthesis method and branch mode synthesis method, the mixed branch mode and constrained mode method is proposed. Furthermore, a mixed two-step method is also proposed on the basis of the mixed method. Results of seismic analysis of soil-multi-story frame interaction system indicate that the mixed two-step method could analyze superstructure and soil separately with the consideration of material nonlinearity. It is also beneficial to consider the effect of soil-structure interaction by only analyzing the superstructure model while using the professional design programs.