Dynamic Research On Lateral-torsional Coupling Of Soil-asymmetric Stucture Interaction System

The response of the structures will be lateral-torsional coupling because of the irregular distribution of the mass and the stiffness of the asymmetric-plan structure, of which the center of the inertia force and the resistant force will be unlined. At present, the researches on lateral-torsional coupling of asymmetric structures are not enough, especially the coupling problem considering soil-structure interaction. In fact, the responses of asymmetric structure are effectted by the soil condition. So, it is necessary to do parametric research on lateral-torsional coupling considering foundation interaction, which is mean much to complete the theory of structure seismic design and to complete the seismic design specification.This dissertation is a part of the national science foundation subject"Research on lateral-torsional coupled systems including asymmetric structure-foundation-soil interaction"(the code number: 50878143). The coupling response of soil-asymmetric structure interaction system, soil-asymmetric structure interaction system considering asymmetric foundation and two-tier building with foundation interaction were researched into. Lateral-torsional coupling vibration equations of soil-asymmetric structure system were established based on the Lagrangian energy method. Supposing that the structure have classical mode shape, this paper used the modal analysis method to the superstructure individually and got the analytical solution in frequency domain. The main impact parameters influencing the lateral-torsional coupled response are determined and the influencing rules of factors on lateral-torsional coupling effect of the interaction system were thoroughly analyzed. The parametric research on elastic dynamic response of soil-asymmetric interaction system in time domain was done by directed integral program, which verified the feasibility of using time history method to do parametric research. According to those analyses, the main results are gained as follow.(1)The main impact parameters influencing the lateral-torsional coupled response are determined: torsional to translational frequency ratio ?, eccentricity ratio B, the foundation properties and the height-to-base ratioλh. It is concluded that the natural frequency and the displacement magnitude of the structure will decrease because of the foundation interaction. The softer the soil, the more decreasing it happened; The influencing rules of eccentricity ratio and torsional to translational frequency ratio to the coupling response would be influenced by the soil condition; the torsional-translational coupling level is decreased because of the foundation interaction. The softer the soil is, the more decreasing it happened(2)The influence rules of asymmetric foundation on soil-irregular structure system are studied. It concluded that mass eccentricity of foundation has slightly impact on the structure, but the stiffness eccentricity has a great influence on the structure, especially on the torsional response. So, it is more important to control the stiffness eccentricity in practical engineering.(3)The main impact parameters influencing the lateral-torsional coupled response are determined: eccentricity ratio, torsional to translational frequency ratio, the location of the eccentric floor and the foundation properties. Eccentricity ratio amplify the displacement of the eccentric floor but reduce the displacement of the non- eccentric floor; the displacement of the uniform eccentric structure are increased following the increasing of eccentricity ratio; the relative relationship of displacement between different eccentric structure lies much on the soil condition.(4)Directed integral program in time domain are used to verify the feasibility of forced decoupling method by comparing the result derived by directed integral program with inverse fast Fourier transform of result derived by forced decoupling method. The parametric research on elastic dynamic response of soil-asymmetric interaction system in time domain was done by directed integral program, which verified the feasibility of using time history method to do parametric research.(5)In order to control the torsional response, code for seismic design of buildings gives two parameters: displacement ratio and period ratio. It concludes that the limited period ratio would depend on foundation properties by analyzing the influence of soil-structure interaction on period ratio. So, we suggest a thorough analysis on limited period ratio considering soil-structure interaction. A more scientific specification sould be made to guide the practical engineering fitting reality.