Reliability-based design criterion for TLP tendons

This paper presents a methodology to perform a Load and Resistance Factor Design (LRFD) criterion for the design of Tension Leg Platform (TLP) tendons in their intact condition. The proposed design criterion considers the Ultimate Limit State (ULS) for the tendon sections, expressed in terms of the expected value of the extreme Interaction Ratio (IR), considering long-term storm sea states, and takes into account the dynamic load effects interaction and the statistics of its associated extreme response. The partial safety factors are calibrated through a long-term reliability-based methodology for the storm environmental conditions in deep waters of the Campeche Bay, Mexico. Different target reliability values are considered in order to evaluate the effect of this key parameter on safety factors. The results show that the partial safety factors reflect both the uncertainty content and the importance of the random variables in structural reliability analysis. When tendons are designed according to the developed LRFD criterion, a less scattered variation of reliability indexes is obtained for different tendon sections across a single or a variety of TLP designs. Finally, it is observed that the target reliability value has a strong influence over the safety factor values and thus over the final size of the structural elements.