Evaluation of Fatigue Design Curves for a Double-Side Welded Connection Used in Offshore Applications

Abstract

One of the major concerns in offshore structures are the welded connections where fatigue failures are highly relevant. In many cases of offshore welded connections, the fatigue cracks initiated may grow from the weld to the base material, but also from the root of the weld. In this study, the evaluation of design S-N curves for a double-side welded connection made of S355J2 steel used in offshore applications is proposed. The characteristic fatigue curve of the double-side welded connection is obtained using statistical analyses based either in the ASTM E739 standard as well as the probabilistic fatigue model proposed by Castillo & Fernández-Canteli. This study concludes with a comparison between the experimental fatigue curves obtained and the design S-N curves proposed in design codes for offshore structures. Existing code recommendations are very conservative when comparing the design S-N curves with the proposed new characteristic S-N curves. For the joint under investigation the hot spot and nominal stress approaches yield very similar S-N results.