Partially Embedded Rectangular Foundations: A Simplified Approach to Compute Dynamic Stiffnesses

Partially embedded rectangular foundations are considered. Soil at the side of the foundation is decoupled from that at the base and is treated as a stack of horizontal layers of unit thickness that are mutually uncoupled. The side soil stiffnesses/depth are formulated from the vibration of a massless rigid rectangular disc in an individual layer. In the development of formulations, the layer medium is further simplified with a column-spring system. All these simplifications lead to simple expressions suitable for practical use. The two parameters in these expressions are defined by iteration using two coupled simple equations. Dynamic soil stiffesses at the side are computed for foundations of rectangular base with various aspect ratios. Despite significant simplification, the developed expressions enable us to compute the side soil stiffnesses for rectangular foundations reasonably close to those computed by a far rigorous approach. An example of its application is provided

Prediction of Non-Linear Pile Foundation Response to Vertical Vibration

A rational and yet convenient approach is presented to account for the dynamic soil-pile interaction in the vertical vibration analysis of a nonlinear pile foundation. Once elastic soil properties and static complex unit load transfer curves are provided, the approach is capable of reproducing the dynamic and nonlinear conditions mutually coupled. The concept of the approach is verified by numerical analyses. The proposed approach is demonstrated for the prediction of vibration response of a selected pile foundation in the field. Both static load tests and vibration tests were conducted previously on this pile foundation. Inputs for the analysis are obtained from the previous static test results. The comparison of the predicted responses with those observed indicates that the proposed approach appears to be reasonable

Nonlinear Time Domain Numerical Model for Pile Group Under Transient Dynamic Forces

A computational model of soil-pile interaction behavior in pile and pile group was developed in this paper. Particular attention was paid to making the model simple and capable of taking into account nonlinear soil behavior, such as gapping and slippage between soil and pile, and cyclic behavior of soil. The model was developed within the frame work of the Winkler model defined in plane strain conditions. In order to analyze transient dynamic response in a rigorous manner, the model was formulated in the time domain using a step-by-step method. A transfer matrix approach was also adopted in the response computation. The proposed nonlinear model was verified with rigorous solutions and the nonlinear behavior with gapping and slippage were discussed based on the computational results

Seismic Response Analysis of Pile-Supported Structure: Assessment of Commonly Used Approximations

The seismic response of a pile-supported structure is formulated by the approach developed by the first author. Using this formulation, some of the crude approximations frequently used in the seismic response analysis of a soil-pile-structure system are examined. Those involved in the analysis procedure are assessed under the linear elastic condition. A commonly used nonlinear soil model for the dynamic pile response analysis is also assessed. It is found that those approximations routinely used in the analysis procedure and numerical modelling can cause significant errors in the computed response of a pile-supported structure

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