Structural Responses of Offshore Jacket Platform Subject to Seismic Ground Acceleration and Wave Forces

Abstract

In this paper, the effect of seismic ground acceleration on offshore platforms in the Malaysian waters has been investigated. In the Malaysian region of South China Sea, the conventional practice applied to design of offshore structures is to assume that forces induced on the platforms due to waves, current and wind control the overall response of the structures. Seismic analysis is not conducted since Malaysia is not located in a seismic-sensitive zone. Local standards have been lacking in recommendation to include seismic ground motion in the design. However, recent earthquake events from far-field have been felt by the platform operators in Malaysian waters and new perceptions in the field question the validity of this assumption. A series of computer-driven dynamic spectral earthquake analyses has been carried out for a jacket-type fixed offshore platform using the finite element software SACS. By incrementally changing the inputs for ground acceleration, the dynamic behavior of the 3D model of the platform is investigated. The result defines the threshold, at which the ground motion induced forces control the structure. Further, a combined analysis of both seismic and wave forces have been carried out, as to define how the two different types of forces contribute to the resulting stresses and deflection of structural members respectively.

Keywords: Seismic, offshore structures, South China Sea