The objective of this paper is to illustrate the application of structural reliability methods for calibration of safety factors for tubular joint design. Reliability assessment models for Ultimate Limit State (ULS) are developed. Uncertainties involved in the assessment and calibration are assessed and measured. Comparisons between API prediction and tests are made to estimate the model uncertainty. The target reliability levels, which depend mainly on the consequences of failure and safety philosophy, are reviewed and discussed. Sensitivity studies are performed to identify critical factors affecting failure probability. A case study is given to demonstrate the procedure of calibrating safety factors by applying structural reliability. The proposed procedures may also be applied to the calibration of safety factors for design of marine pipelines, ships and other structures.

INTRODUCTION

To ensure safety of offshore platform, codes and rules are made for the planning, design and construction of offshore platforms by API, DNV, etc. Besides conventional deterministic rules, API have developed LRFD rules for design of jackets (API RP2A, 1993). API RP2A code is widely used in offshore oil and gas exploitation. The international Standards Organization (ISO) has undertaken an effort to develop guidelines based on reliability methods (ISO, 1994, 1995). During the last two decades, many efforts have been given on structural reliability and their application to practical structural engineering. The experience from other structures have been valuable in the extension of this process to offshore, with the issue of the load and resistance factor version of API RP2A code (API, 1993). This approach not only requires evaluation of the ability of a structure to resist the applied loads but also evaluation of these loads in probability terms. Also, the development of an alternative based on reliability methods to the existing practices of API RP2A has been started years before (Lloyd and Karsan, 1988) and several projects related to this topic have been reported.

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