Load resistance factor design (LRFD) calibration of load factors for extreme storm loading in Malaysian waters

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Load resistance factor design (LRFD) calibration of load factors for extreme storm loading in Malaysian waters

Nichols, N W / Khan, R / Rahman, A A / Akram, M K M / DrChen, K

Petronas Carigali Sdn Bhd (PCSB) performs its operations in three regions in Malaysian waters. Currently, fixed offshore structures are designed in accordance with ISO 19902, which is meant to provide guidance for the design of fixed offshore structures internationally, but the load factors in ISO 19902 are often derived from studies performed in the Gulf of Mexico and the North Sea environments. One such load factor is the 1.35 for environmental loading that has been prescribed within ISO 19902. Site specific metocean studies in Malaysian waters reveal environmental conditions that are more benign than the Gulf of Mexico and the North Sea. This study presents the results of a component-based approach and investigates the suitability of the 1.35 load factor for environmental loading in Malaysian Waters to achieve the same target reliability for a similar structure designed consistent with the provisions of the API RP 2A-WSD. First-order reliability methods (FORM) have been undertaken using a database of tubular components with representative geometries, bending-to-axial stress ratios, dead-to-live load ratios and environmental to gravity load ratios. The analysis results show that if the target were to be based on the weighted average probabilities inherent in the API RP 2A-WSD 21^st Edition, an environmental action factor of 1.245 (Region A), 1.295 (Region B) and 1.255 (Region C) with the ISO provisions will on average achieve similar reliability.