The Research On Nonliear Soil Structure Interaction And Structural Seismic Isolation Based On SSI Effects

Along with the development of the human society, and with the centralizing of fortune and population ,the damage caused by earthquake disaster to our society goes up greatly, and so, the importance of performance based seismic design has been more widely recognized. Performance based design requires, however, more accurate analyses, including all potential important factors, in order to predict the expected level of damage associated with a given level of earthquake. Just because of this, the majority of researchers and technical staff working in practice have recongnized the the necessity and advantages to design the structures based on the analysis with the soil-foundation-upper structure considered in an overall system. In the soil-structure interaction system, the strong non-linear soil characteristics and their impact on SSI is one of the core problems. And in further, the idea of isolating the upper structures based on the SSI mechanism is an innovative idea, which deserves significant practical studying.This article focuses on the nonlinear dynamic characteristics of field soils as well as its suitable constitutive model. Keystones of the research are soil nonlinear dynamic properties and its impact factors, impact of non-linear soil behavior on both free field seismic reponse and the soil - structure system dynamic response during earthquakes and the mechanism of these impacts. Around these focuses, experiments are adopted to study the features of the soil-structure interface behavior and the impact of relative rigidity of the upper structure and the foundation on the SSI effect of soil-structure system, for the purpose of providing reference for both further theory research and practical applications. Finally, according to the inspiration of SSI analysis, the idea of isolating the upper structure with artifical soft interlayer between the shallow foundation of the rigid upper structure and the relative rigid field is advanced. The main work and innovation of this text are as follows:1. With the summarization of lots of interrelated references, the studying actuality and developing level which about soil-structure interaction are presented. The limitations,advantages and disadvantages existing in present researches are discussed too. Then the basic theory way and analyzing frame route related to soil structure interaction in this paper is introduced.2. With the use of cyclic simple shear testing, the nonlinear dynamic properties of a certain kind of silty clay are probed. The feasibility of graded cyclic loading test method with the loading amplitude increase gradully on a soil specimen to get the dynamic properties of soil is validated by the experimental research. Also the effect of accumulated volume strains which caused by the cyclic loading history on the dynamic properties of soil and the effects of consolidation pressure which usually caused by the deadweight of the field soil on the dynamic properties of soil are researched respectively, and accordingly an accumulative strain strengthened dynamic model and an consolidation pressure relative dynamic model are brought out in the further study.3. A new damping based real nonlinear hysteretic model is advised, and further this model is extended into the elasto-plastic domain so that a damping based boundary model is constituted. With the Comparation of the model numerical realization and the cyclic simple shear testing results of a real soil, it is proved that the soil nonlinear model carried out in this paper is ascendant and proper.4. A new free field seimic reponse analysis program is build up, and then with the application of the dynamic property model and constitutive model advised previously, the effect of soil nonlinear behavior on the free field seismic response is researched, in which the influence of a series factors such as the bottom boundary condition, soil constitutive model, and the existing of soft interlayer, etc, on the free field seismic reponse is dicussed.5. A series cyclic simple shear tests aimed to discuss the nonlinear shear stress-strain relations of the interface between a silty clay and concrete are carried out. In these tests, several factors which may have effects on the interface behavior are investigated, such as the roughness of the interface, the vertical pressure on the interface, the thickness of the soil specimen beside the interface, and the shearing with unilateral or bidirectional loading. Based on the test result, a modified constitutive model for the finit thickness thin intereface element is suggested.6. Large scale model experiments are carried out in order to survey the effects of rigidity ratio between the upper structure and the foundational structure on the soil-structure interaction effects for the fisrt time. Based on the experimental reslults, benificial suggestion is brought forward for the code on how to decide the additional period of structure as the SSI effects taking in considerated.7. With proper finit element model of the SSI system builded up in the general software MSC.Marc, and with the use of the damping based boundary soil contstitutive model and the modified finit thickness thin interface elemental constitutive model, the effects of soil nonlinear behavior on the structural seismic response as well as the mechanisms of these effects are analized to a deep extend, and the structural response spectrum with the soil nonlinearity in consideration is carried out for the purpose of practical application.8. An innovate idea that using the soft interlayer between the rigid field and rigid shallow foundation as the base isolation material is brought out, and analysis case is carried out to validate the isolation effects of soft interlayer as well as the impact of some factors on the isolation effects. Lastly, advice and prospect on the artifical soft soil research is given.