Parametric Analysis And Experimental Research Of Seismic Response Of Soil-eccentric Structure Interaction System

With the rapid development of urbanization in China, more and more asymmetric buildings with irregular distribution in horizontal and vertical direction appeared. The seismic responses of such buildings are of torsionally coupled features typically. Previous earthquake damage investigations indicate that the vibration characteristic of eccentric structures can be notably altered by the flexibility of foundation soil, while the soil-structure interaction effect may enlarge the vibration response of super- structure. Since the complexity and computational scale will be increase significantly when incorporating the SSI effect into relative research. The provisions for structure eccentricity and torsion-resistant design in most design codes are based on fixed-base assumption, while the influence of SSI effect is not fully considered. Therefore, an analytical approach that retains the essential characteristics necessary for studying the torsionally coupled seismic response of eccentric structure built on flexible foundation with reasonable computational cost is presented in this dissertation.A series of innovative work has been done on the issue, the achievements and conclusions of which can be draw as follow:(1) The research status of soil-eccentric structure interaction is classified and discussed. An analytical approach that retains all the essential characteristics for simulating the SSI effect is presented and formulated based on the branch mode theory. The superstructure and foundation branch are coupled through mode aggregation procedure. Parametric study of single-storey eccentric structure (2DOF) is firstly carried out by comparing the transfer function results of translational and torsional response, in which the DOFs of foundation soil are incorporated in the explicit solution of superstructure. The influence of torsional to translational frequency ratio, eccentricity ratio, eccentric form, height-to-base ratio and foundation flexibility are analyzed systematically.(2) Since the foundation model usually consists of a large amount of continuous soild or plane elements, the computational scale is much higher than that of superstructure. Previous reaseraches indicate that the distribution of foundation modes is extremely scatted among all the modal analysis results, which makes it rather difficult to define the mode cut-off criterion. As a replacement of traditional modal vectors, Ritz vectors are employed in the solution of foundation mode which can filter the lower ranking mode of negligible contribution to the foundation vibration by taking the spatial distribution of external loading into consideration. The results of sample analysis show that Ritz vectors may significantly boost the solution efficiency of natural vibration, which is very suitable for the modal analysis and seismic analysis of foundation sub-structure.(3) Based on the research of single-storey eccentric structure interaction system, the computational theory of multi-storey eccentric structures considering SSI effect is developed and formulated. Parametric analysis is carried out by numerical methods, since the number of DOF of superstructure exceed the limitation of explicit solution. The magnitude and rules of influence of parameters, such as floor eccentricity ratio, general ratio of torsional to translational frequency, relative stiffness of soil to structure, distribution of eccentric floor and relative eccentricity between floors, are analyzed and discussed comprehensively.(4) Shaking table test for soil-pile-eccentric structure interaction system is carried out and compared with fixed base foundation test. During the preparatory stage, a series of improvement has been presented for model similitude design, fabrication of model soil and the dynamic performance test of soil material. The vibration characteristics of interaction system, constitution of eccentric super- structuctre response, acceleration and strain response, vibration response of group piles and foundation soil are measured and analyzed, which provides experimental reference to theoretical research.(5) The direct integral program for soil-eccentric structure interaction system is established base on the Wilson-θalgorithm. The feasibility of the analytical approach developed in this paper is verified by comparing the time domain results derived by inverse fast Fourier transform procedure with the time-history curve of superstructure response obtained by direct integral program. Since the difference between shaking table test conditon of SSI system and theoretical assumption is not neglectable, the analytical results are compared for general rules, which proved the tendency of parameters influence of structure eccentricity and foundation flexibility on the torsionally-coupled response.