SPECTRAL FATIGUE ANALYSIS PROCEDURE FOR JACKET OFFSHORE STRUCTURES

Fatigue remains a critical design and assessment challenge for offshore jacket structures operating under cyclic wave loading throughout their service life. Spectral fatigue analysis offers a robust framework for assessing cumulative damage by combining environmental loading spectra with the dynamic response of structures. This article presents and demonstrates a structured spectral fatigue analysis procedure for jacket platforms, implemented using SACS software in accordance with ISO 19902 and API RP 2A guidelines. The procedure encompasses model calibration with hydrodynamic coefficients and corrosion allowances, derivation of the Centre of Damage (CoD) wave, equivalent linearization of soil–pile interaction, evaluation of natural frequency and mode shape, wave response simulations, transfer function generation and fatigue life estimation using the Palmgren–Miner rule. Application to a 54.5 m water depth jacket platform highlights critical hot-spot stresses at tubular joints, with one joint exhibiting a fatigue life of only 12.94 years. The novelty of this study lies in bridging theoretical formulations with explicit software-based implementation, offering a transparent, stepwise framework that links metocean data, structural dynamics and fatigue assessment outputs. The proposed methodology contributes to advancing best practices for offshore structural design and integrity management, providing a replicable reference for both academic research and industrial applications.