Reliability Procedure for Fixed Offshore Platforms

This paper presents a method for calculating the notional risk of overload associated with fixed offshore platforms subjected to random wave loading. The lifetime exposure of the structure to potentially damaging storms is treated within a rigorous mathematical framework. The procedure used to establish the long term extreme wave load distribution is emphasized. This procedure utilizes presently available oceanographic information in a statistical model of the wave environment. The composite probability of exceedance associated with all significant loading events is computed for a lifetime exposure to the ocean environment. For the purposes of demonstrating this procedure, only the resistance of pile foundations to overturning forces is investigated. A simplified technique for estimating the ultimate foundation capacity is presented and compared to a more rigorous method. Failure mechanisms in the jacket are not investigated, i.e., the structural jacket is assumed to be adequate to transfer loads into the pile foundation. Finally, the resistance and load effects are combined to evaluate the reliability of the pile foundation in a wave environment. Results are presented for a recently installed Gulf of Mexico platform. The sensitivity of the results to various input parameters is discussed.