Development of Calibrated Deterministic Design Approach for Design and Assessment of Offshore Structures Exposed to Environmental Loading

Abstract The integrity of offshore structures is commonly demonstrated by proving the structure has sufficient strength to pass code-based strength checks (limit states). Hence, the reliability of any structure exposed to environmental loading from waves, wind, etc. is inherently linked to the requirements of codes and standards. Design requirements in European codes and standards for onshore structures are commonly calibrated to link code compliance to acceptance criteria expressed in terms of target annual probability of collapse. However, this is not generally the case for codes and standards used in the offshore industry to verify structural integrity and so designers, asset owners etc. of offshore installations will usually not know the failure probability of their code compliant structures. In 4 the common design criteria for the most important offshore code, ISO19902 5 has been (re-)assessed, and a huge variability across a range of different failure mechanisms is found. In other words, the reliability of code compliant structures is far from uniform: it depends upon the structural configuration, the environment at the installation site, and the location (within the structure) of the weakest failure mechanisms. The result is that structures either have a too low or too high failure probability and cost-benefit is not optimized as a few weak links may control integrity, while major parts of the structure are relatively too strong. To mitigate the above, we have used a newly developed SRA model 3 that accounts for non-breaking, spilling-breaking and plunging-breaking 3D waves, to calibrate a deterministic engineering approach to align with user defined target failure probability. The work is described in the present paper.