ENVIRONMENTAL LOAD FACTORS AND SYSTEMSTRENGTH EVALUATION OF OFFSHORE JACKET PLATFORMS
API RP2A Working Stress Design (WSD) forms the basis of offshore steel Jacket platform design all over the world and has proved to be accepted design standard since it was first issued in 1969. WSD is a factor of safety-based code which is derived from WSD theory and reduces the ultimate resistance strength to allowable stress for safe design. In WSD. minimum resistance results from test results of yield strength and for load from past experience; thus, safety factor was inherent in these codes though not apparent. Since the loads/resistances are varying, the assumptions used in WSD design process, i.e. a single factor of safety for all load combinations, cannot maintain a constant level of structural safety. WSD method uses safety factors without taking into consideration the uncertainties, and it assumes that all variables are deterministic. Thus, safety of platform is achieved by WSD through the use of a factor of safety against the inherent uncertainties of load and resistance. For allowable stress design, safety of structure is achieved by the use of a safety factor against the uncertainties of load using some arbitrary experience and judgment like 1/3 decrease for allowable stresses. This method provides no knowledge about effects of various random variable parameters on the safety of Jacket platform...
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