A Comparison Between Modal Push-Over and Nonlinear Dynamic Response of Jacket Type Offshore Platforms Subjected to Strong Ground Motions

Abstract

Nonlinear dynamic analysis for offshore structures has been a major challenge in marine structures and earthquake engineering. Nonlinear Dynamic Analysis of the structures subjected to strong ground motions is the most reliable prediction method. This method is very complex and expensive. An alternative procedure that has found to be much applicable in recent years is the nonlinear static analysis called push-over analysis method. Many attempts have been made to improve the predictive capabilities of the push-over analysis, particularly by employing adaptive load patterns and accounting for higher modes of vibration effects through modal push-over. In this paper, modal push-over analysis (MPA) of jacket type offshore platforms considering soil-pile-structure interaction subjected to strong ground motion has been studied and the results have been compared with “exact” nonlinear response history analysis (NLRHA). A jacket type offshore platform includes of piles, jacket and deck with different behaviors during strong ground motion. In this paper, three-dimensional model of jacket and pile has been considered using a combination of finite element method (FEM) and beam on nonlinear winkler foundation (BNWF) approach in an integrated model. Both jacket and pile elements have been modeled using fiber sections. The model has been developed using Open System for Earthquake Engineering Simulation (OpenSEES) software. In this paper, nonlinear seismic analysis of a new designed jacket type offshore platform located in Persian Gulf subjected to different levels of earthquake has been performed and the results have been compared with MPA ones. It can be concluded that the error percentage in MPA procedure is negligible when more modes of vibration are participated in the evaluation of the structure behavior.