Design and Reliability Analysis of Braced Monopod Platform in Natuna Sea
Gary Prayogo 1 dan Rildova 2
Program Studi Teknik Kelautan
Fakultas Teknik Sipil dan Lingkungan
Institut Teknologi Bandung
Jl. Ganesha 10 Bandung 40132
1 antonius.gary22@gmail.com dan 2 rildova@ocean.itb.ac.id
Abstract: Various analysis is conducted to ensure the survivability of an offshore platform in any environment conditions during its service life, such as in-place analysis, seismic analysis, and fatigue analysis. Offshore platform is designed based on a standard, commonly API RP-2A WSD. An offshore platform is designed for operating in Natuna Sea. Its design life is 20 years. It must survive in operating and storm condition, also in the minimum and maximum water level based on the in-place analysis result, by checking the member’s stresses, serviceability in deflection, and joint punching shear. The structure is also designed to survive in strength level earthquake, by the same checking method as in the in-place analysis. Its service life is 29.1 years (with 2.00 safety factor) and the fatigue damage 0.68732 in the fatigue analysis result. Working stress design principle, used for designing an offshore platform, produce inconstant safety index caused by the variability of environment load. API RP-2A LRFD was published to produce structure with more constant safety index. Load and resistant factor design principle apply various load factors to differentiate the variability of each load applied to the structure. The applied Extreme environment load factor, its value is 1.35, was taken from the Gulf of Mexico seas condition, may be different in the Indonesian seas. In this Final Project, a reliability analysis is conducted to two different structure, optimized in extreme environment condition based on WSD principle and LRFD principle. The result is safety index or reliability index. The reliability index of WSD’s structure is 3.6068 and the reliability index of LRFD’s structure is 3.7478. LRFD’s structure has larger reliability index. The reliability index of WSD’s structure is not satisfied to the target of high-risk class from Bai and Jin (2016), with the target value of 3.72. However, the LRFD’s structure is satisfied with that target of reliability index.
Keywords: Offshore Platform, wave, structure analysis, pushover analysis, reliability analysis, reliability index.
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