Two-dimensional equivalent stiffness analysis of soil-structure interaction problems

The finite element technique is a powerful method to study the dynamic response of a structure taking into account the effects of ground conditions. However, limitations of computer storage capacity and cost presently prevent its general application to three-dimensional problems. In this thesis it is shown that three-dimensional problems can be analyzed by applying appropriate modification factors to two-dimensional (plane strain) analyses. Modification factors are first determined analytically by comparing the dynamic response of both strip and rectangular footings (uniform shear stress) for a range of input frequencies. It is found that for input frequencies which are less than the fundamental period of the soild layer the modification factor is essentially independent of the input frequency. This suggests that the modification factors could be obtained from static analyses. Modification factors based on static stiffness analyses for both uniform shear stress and uniform shear displacement (rigid foundation) conditions were obtained and were found to be in close agreement with those obtained from the dynamic analyses. Variation of the modification factor with both the depth of the layer and the ratio of the sides of the rectangular base are given in graphical form. These factors may be applied to finite element place strain analysis to predict the dynamic response of three-dimensional structures.Applied Science, Faculty ofCivil Engineering, Department ofGraduat