INFLUENCE OF RANDOM VARIABLE ON RELIABILITY INDEX OF BRACED MONOPOD PLATFORM BASED ON FATIGUE LIMIT STATE IN NATUNA SEA

• Main Author: Prayogo, Gary
• Format: Theses
• Language: Indonesia
• Subjects: Teknik (Rekayasa, enjinering dan kegiatan berkaitan)
• Online Access: https://digilib.itb.ac.id/gdl/view/57083
• Institution: Institut Teknologi Bandung

The uncertainty of load variables affects fatigue reliability of offshore structure. Reliability analysis on several fatigue performance functions was carried out to analyze the influence of the load variable. Braced monopod structure was designed optimally with API RP2A WSD with environmental condition of Natuna Sea. FORM II is used to perform reliability analysis. The reviewed variables are the annual fatigue damage from random waves, S-N curve, and model uncertainty of stress analysis. Annual fatigue damage uncertainty was obtained from fatigue analysis for each 1-year data of 59 years SEAFINE wave data. S-N curve uncertainty recommended from Wirsching (1984) and model uncertainty of stress analysis from JCSS were used. The result is relation graph between structure fatigue life and reliability index for each performance function. Annual fatigue damage uncertainty has the most influence on reliability index and the S-N curve uncertainty is the least. Uncertainty of load variable result in structure that still has reliability at the fatigue life around safety factor (SF) times fatigue design life, with the reliability index is about 50% of structure reliability index (at design life). Structural reliability degrades because fatigue damages are accumulated every year. Uncertainty of S-N curve gives the least influence compared to other random variable, with the degradation of reliability index around 0.1. Reliability index of critical joint of this braced monopod is 1.16.