Random seismic response analysis of jacket structure with Timoshenko's beam theory

Abstract

Today many complex three-dimensional (3D) models, typically finite element method (FEM) models, have been used in the analysis of jacket platforms. However, these comprehensive models are not readily adopted in engineering practice, especially during the preliminary design stage. The main reasons are the large computing resources required and the lack of detailed information for setting up the FEM model. In this paper, a simplified response analysis method is proposed to make preliminary estimate of the random seismic responses on jacket platforms. Based on Timoshenko's beam theory, the equation of bending motion was proposed and solved by using the classical Ritz method combined with the pseudo-excitation method. A computer code for computing random seismic responses was also developed and verified. A six-legged jacket platform was used as an example, whereby three types of Ritz functions were used to illustrate the validity of the model. The results of this study were compared with those obtained from a well-established complex 3D FEM model. The findings of the comparison showed that the accuracy of the simplified model was better than 95%. It was concluded that the proposed simplified method was effective, useful and practical in seismic design of platforms.