EFFECT OF RAFT FLEXIBILITY AND SOIL MEDIA ON THE DYNAMIC-RESPONSE OF A FRAMED STRUCTURE

In this paper, a numerical model is outlined for a three-dimensional (3D) dynamic soil-structure system using 3D frame elements for modelling the superstructure, the combination of thick plate elements and plane stress elements for modelling the raft foundation and the coupled method of 3D finite elements and infinite elements to model the infinite soil medium. After verifying the accuracy of the present method, a general study on the effects of raft flexibility and soil media on the dynamic response of a 3D frame structure including dynamic interaction effects is also performed. The associated numerical results from this study have demonstrated that (1) the present model is very suitable to solve the dynamic frame-foundation-soil interaction problems; (2) the combination of thick plate element and plane stress element should be used to model the raft in the analysis when the system is subjected to the excitation of horizontal earthquakes; (3) the flexibility of a raft must be included in the dynamic analysis of a 3D frame-foundation-soil system so that a realistic solution can be obtained; (4) the layer characteristics of soil media underneath the raft have significant effects on the dynamic response of a 3D frame structure and the softer soil layer will result in greater response of the frame.