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

In this paper, the effect of seismic ground acceleration on offshore platforms in the Malaysian waters will be investigated. In the Malaysian region of South China Sea, the conventional practice applied to design offshore structures is to assume that forces induced on the offshore structures due to waves 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 Malaysia waters and new perceptions in the field question the validity of this assumption. A row of computer driven dynamic spectral earthquake analyses will be carried out for a jacket-type fixed offshore platform (Kumang Cluster F9JT-a) using the finite element software SACS. By incrementally changing the inputs for ground acceleration, the dynamic behaviour of the 3D model of the platform is then investigated. The result will define the threshold, at which the ground motion induced forces control the structure. Further, a combined analysis of both seismic and wave forces will be carried out, as to define how the two differently induced forces contribute to the resulting stresses and deflection of structural members respectively. Lastly, the integrity of the structure will be determined by defining return periods for significant earthquake events.