Application Of Mixed Constraint Modal Synthesis Method For Soil-Superstructure Interaction System

Along with the rapid development of the urbanization and the increasing of the city's population, the issue of land shortage has become increasingly prominent. In this case, multi-story building is gradually adopted since it has advantages such as saving land and making efficient use of architectural space. But our country is sited at earthquake-prone area, and has frequently occurred earthquake since the Wenchuan Sichuan earthquake in 2008 year, so seismic analysis of multi-story building has been paid much more attention among the engineering community. It is necessary to introduce the effect of soil-structure interaction during the structure seismic design and analysis process. Among the existing analysis measures, the dynamic substructure method is widely used in the analysis of soil- structure interaction for it can reduce the degrees of freedom of system, improve the computational efficiency and save the calculation time. But the substructure method is only used in the linear structures. In order to solve this problem, this paper applies mixed linear-nonlinear constrained mode synthesis method proposed by my team to the ANSYS software. The main innovations and achievements as follows:1. The mixed linear-nonlinear constrained mode synthesis method is introduced basing the theory of the constraint modal synthesis method. A seismic analysis of a high-level framework structure is been carried by using mixed linear-nonlinear constrained mode synthesis method in ANSYS software. The applicability theory of the mixed linear-nonlinear constrained mode synthesis method in the analysis software of ANSYS is vertified.2. The implementation method of the mode cut-off criterion based on potential energy criterion in ANSYS software is putted forward. The truncation criterion procedure is written to extract the information of stiffness, quality and fixed interface main modal, numbers of internal nodes and boundary node of each substructure in ANSYS software and handle them using the self-programming into the Matlab software. The application practice of the mode cut-off criterion in substructure analysis is provided.3. The formula of the substructure method using viscoelastic boundary in soil boundary is derived. A seismic analysis of a high-level framework structure with viscoelastic boundary is carried by using the mixed linear-nonlinear constrained mode synthesis method in ANSYS software to discuss the influence of viscoelastic artificial boundary to the substructure analysis. The analysis result is showed that the viscoelastic boundary total freedom degree is not necessarily much smaller than the free boundary, due to the viscoelastic artificial boundary freedom cannot be cut. So the influence of artificial boundary to substructure analysis is small in the cut degrees of freedom and calculation time.4. A seismic analysis of a high-level framework structure without regard the soil material nonlinearity is carried by using the mixed linear-nonlinear constrained mode synthesis method in ANSYS software to discuss the random error of the result without regard the soil material nonlinearity to the result regarding the soil material nonlinearity. The result shows that the soil without regarding the soil material nonlinearity can exaggerate the displacement and internal force of structure in soil-structure interaction analysis. So the Suggestions that it is necessary to considering the material nonlinearity in the soil- structure interaction analysis is proposed.5. A seismic analysis of a high-level framework structure which considers the friction effect of basis and foundation is been carried using the mixed linear-nonlinear constrained mode synthesis method in ANSYS software to analyze the influence of friction calculation to the calculation results of interaction. It is showed that the friction can increase the displacement of the upper structure, and increase the plastic deformation of soil.