Perpustakaan Digital ITB

To fulfil the increasing demand of energy, people are searching for another place to explore oil and gas beside in land. The development of technology found that there are many reserve oil and gas below water. But to explore oil and gas below water, we need building that can hold loads such as environmental load (wind speed, wave height, and current) -beside the usual live and dead load- in operating condition or even in storm condition. That structural building is called offshore platform and they are separated by their specific function such as for process, service, storage or well. One of many problems that can occur during a service life of a platform is subsidence, and currently this platform is undergoing subsidence slowly. This subsidence occurs because of the pressure lost underneath the soil due to exploration of gas. Subsidence is the motion of a surface (usually, the Earth's surface) as it shifts downward relative to a datum such as sea-level. Deck height is the vertical distance from the still water surface to the underside of the lowest deck structural element on the platform. Platform subsidence means that the surface of the sea level below the platform is shift downward which causes the deck height to decrease and make the structure of the platform get additional loads. The additional loads can be caused by the wave that exceeded the deck which was not designed to receive wave load. To analyze platform that undergo subsidence, we use linear and non linear analysis, The linear analysis is carried out by SACS computer Software meanwhile the non linear analysis is carried out by USFOS program. The linear analysis includes in-place analysis and fatigue analysis, and the non linear analysis explicates push-over analysis. The output is used to determine whether the platform can hold its structural integrity to withstand all existing loads or not.