The Application of Finite Element Method in the Seismic Design of Offshore Structures

This paper on "The Application of Finite Element Method in the Seismic Design of Offshore Structures" was presented at the NAFEMS World Congress on The Evolution of Product Simulation From Established Methods to Virtual Testing & Prototyping - 24-28 April 2001, The Grand Hotel, Lake Como, Italy.

Abstract

Offshore structures installed in seismic areas must be designed, like any other type of structure whether they are buildings serving the general public or industrial facilities providing essential services, to have adequate strength and sufficient ductility to prevent collapse during the maximum credible earthquake (MCE). This paper addresses the major aspects that should be considered in the numerical analysis used in the seismic design of an oil platform through a case study. It highlights the importance of selecting the most appropriate arrangement for the connection between the steel Topside and the concrete Substructure and its effect on the seismic performance of the platform. The advantages of performing a detailed global 3-D non-linear analysis of the whole structure in order to predict its dynamic performance during a seismic event, is discussed. In addition, the benefit of performing a detailed finite element analysis on certain parts of the structure, such as the deck connection, is demonstrated. The seismic global analysis showed that the seismic performance of the platform is satisfactory, with plastic hinges developing in a small number of elements in the Topside structure. The detailed FE analysis, which was performed on the deck connection, determined the depth by which the top and bottom stiffeners had to be extended to prevent local buckling at both ends of the steel legs.