Influence of random variable on reliability index of braced monopod platform based on fatigue analysis in Madura North Java Sea

Abstract

This paper carried out fatigue reliability analysis on braced monopod structure located in Madura North Java Sea to find the most suitable fatigue performance function so better service life prediction of each structure’s components can be done by testing the influence of some load random variable. Fatigue reliability analysis is a local analysis therefore analysis will be conducted only on four critical joints. Reliability analysis is done on several performance function using First Order Reliability Method (FORM). The load random variables which will be tested are yearly fatigue damage, local and global stress analysis, and S-N curve parameter. Randomness of fatigue damage is obtained by running fatigue analysis using only one-year wave data for 59-year SEAFINE wave data. Fatigue damage from analysis will be divided by safety factor and service life to obtain yearly fatigue damage. Reliability index from several performance functions show S-N curve parameter hardly influence the result of reliability analysis. Therefore, fatigue reliability analysis will only include yearly fatigue damage and local and global stress analysis as load random variable. Reliability index with 2 as the value of safety factor and 20 years of service life for four critical joint which are 301L, 303L, 203L, and 201L respectively are 1.24, 1.30, 1.30, and 1.30.