Probabilistic Analysis of Live Loads on Offshore Platform Piles

Abstract

Relatively accurate techniques are available to assess structural behavior under given loads, yet the loads themselves remain an estimate based in part on field measurements, in part on professional logic and experience, and in part on trial and error. The design of piled foundations for fixed offshore platforms must consider operating and extreme weather conditions. In the operating condition, the magnitude of live loads on open areas of topside structure is an important consideration. Unfortunately, the design live load intensity that applies to open areas on offshore platforms is not identified in international codes and standards. There does not appear to be any consensus on the value to be adopted in the industry. Some operators suggest the open area live loads need not be considered for pile foundation design, while others stipulate values such as 10 kPa. This is partly due to the variability associated with the different live loads sources. The objective of this study is to obtain a better understanding of open area live loads on offshore platforms and develop a methodology to obtain the long-term and extreme open area live load. A load survey was conducted for the purpose of this study, and a probabilistic analysis was carried out to derive the maximum axial load on piles that is expected during platform lifetime. The results of this study indicate that the use of a single value for the open area live load (OALL) may not be appropriate and suggest appropriate values for Load Resistance Factor Design (LRFD) or Working Stress Design (WSD) methods.