DYNAMIC RESPONSE OF A SINGLE PILE t USING SEMI-ANALYTICAL FEA

Abstract

Pile foundation has been very much popular in recent years, not only for carrying vertical but also the lateral loads. Pile foundations are generally preferred when heavy structural loads have to be transferred through weak soils to firm strata. These foundations are subjected to significant amount of lateral loads, besides vertical loads. The lateral forces may be due to the action of wind in case of offshore structures, and combination of wind and wave action on offshore structures. Apart from these, other cause of lateral loads may be earthquake forces, heavy machines, vibration due to some construction or demolition action being carried out nearby the structures, etc. In the present thesis a parametric analysis is conducted to study the effect of pile dimension and soil modulus on the dynamic response of the pile. The study is conducted on soil-pile model of different pile diameter and soil modulus, and results are compared to get the effect. The soil — pile system is modeled using finite element method. The programming is done in Matlab, as the FEM involves computation and handling of very large scale matrix that is relatively very simple in Matlab. Time-history analysis of model is done for varying circular frequency of load and the results are compared to get the resonant frequency of system in each case. Maximum possible bending moment for the dynamic excitation of pile is also computed. The result shows that resonance occurs normally at lower circular frequency as at higher frequency the maximum amplitude reached reduces to great extent and the damping becomes very influential. Result also shows that the maximum bending moment normally doesn't occurs at the resonance or maximum deflection point, and so to get the detail of maximum bending moment and its depth of occurrence, proper dynamic analysis is required.