Development and Verification of Template Offshore Capacity Analysis Tools (TOPCAT)

Abstract

Abstract This paper summarizes development and application of the suite of computer programs identified as TOPCAT (Template Offshore Platform Capacity Analysis Tools). TOPCAT provides high utility, simplified analyses of storm, earthquake, and operating loadings, the capacities of the primary structural components that comprise template-type platforms, the fatigue of important structural details, and the reliabilities of the primary structure and foundation components. The loading and capacity algorithms in TOPCAT have been verified with results from detailed nonlinear analyses, with performance characteristics of platforms subjected to intense hurricane loadings, and with data from large scale tests. These verifications have shown that TOPCAT can develop essentially unbiased results with a small coefficient of variation. TOPCAT has proven to be valuable in performing screening analyses for platform requalifications, in development of platform IMR (inspection, maintenance, repair) programs, in reliability and parametric analyses, in preliminary design of new platforms, and in providing verifications of results from detailed analyses. Introduction The work to develop TOPCAT was initiated in 1993 in a project that was performed for UNOCAL in the Gulf of Thailand. This project involved developing preliminary estimates of the lateral loading capacities of template platforms subjected to extreme condition typhoons. A technique identified as ULSLEA (Ultimate Limit State Limit Equilibrium Analyses) was formulated and applied during this project.1, 2,3,4 Comparisons of results from ULSLEA with those from sophisticated nonlinear analyses indicated that ULSLEA could produce storm loadings and capacities that were very close to those developed with the sophisticated programs.5,6,7 Additional testing developed similar results.8,9 In 1994, a joint industry - government sponsored project was initiated to continue this development. The culmination of this project was development and verification of the computer program identified as TOPCAT (Template-type Offshore Platforms Capacity Analysis Tools). This paper summarizes the background of this development and the verifications of the analytical results. To date (2000), TOPCAT has been verified with results from more than 100 cases involving analyses from several sophisticated nonlinear analysis computer programs. In addition, it has been verified with results from studies of platforms that have failed, been severely damaged, and survived severe hurricanes,9,10,11 and with results from large scale frame tests.12 Applications of LSLEA / TOPCAT have demonstrated the high utility of a simplified suite of computer programs that can be used by engineers to perform 'back of the envelope' analyses. These analyses have proven to be valuable in screening platforms for requalifications,2,4,13-16 in development of IMR (inspection, maintenance, repair) programs,17,18 in performing reliability and parametric analyses,19,20 studying the damage tolerance of 'minimum' structures,21,22,23 validating results from complex and sophisticated analyses,11,24 and in preliminary design of new platforms. Background TOPCAT enables a user to quickly develop a simple structural model for several standard platform types and then analyze the model for the following conditions:25