Evaluation of Storm Loadings on and Capacities of Offshore Platforms

Abstract

Currently, there are approximately 3,000 major platforms offshore the United States and an equal number of platforms offshore other countries around the world. Approximately one-third of these platforms have exceeded their design lives and are now being called on for extended service. Reassessment and requalification of this massive infrastructure has required development of new engineering procedures. This paper summarizes development of a simplified procedure to evaluate storm loadings imposed on offshore platforms and to evaluate the ultimate limit state lateral loading capacities of such platforms. Verification of these procedures has been accomplished by comparing results from the simplified analyses with results from three-dimensional, linear, and nonlinear analyses of a variety of template-type platforms. Several of these platforms failed, were near failure, or survived loadings from severe hurricanes. The simplified procedure is able to replicate the loadings and capacities indicated by the complex analyses. Verification of the second-generation procedures indicate lateral capacity biases (ratio of result from nonlinear analysis to result from simplified analysis) in the range of 0.80–1.26 with a mean value of 0.95. The simplified procedure is able to replicate the observed performance of the platforms. These methods can be used to help reassess and requalify platforms that are being evaluated for extended service. Because the simplified procedure is much less prone to human errors, this procedure can be used to help verify results from complex analytical models.