INFLUENCE OF RANDOM VARIABLE ON THE FATIGUE PERFORMANCE RELIABILITY INDEX OF BRACED MONOPOD PLATFORM IN MAKASSAR STRAIT

• Main Author: Junsasmi Tambunan, Almaidah
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/70325
• Institution: Institut Teknologi Bandung

<p align="justify">Offshore platforms that are designed need to consider the uncertainty factor to avoid structural failure. Fatigue in tubular element welded joints is a limit state reviewed in this study. The limit state can be expressed in the form of a random variable of capacity and a random variable of load. The structure is said to fail when the load exceeds the capacity of the structure. Reliability analysis is carried out to obtain the probability of structural failure or it can also be expressed in the form of a reliability index. The reliability index is used to review the structural capacity over its service life. The greater the reliability index value, the more reliable the structure will be. In addition, the reliability index can also be used to determine the value of the safety factor. The structure designed in this study is a braced monopod platform in Makassar Strait. In this study, reliability analysis was carried out using the First Order Reliability Method (FORM II) on five fatigue performances. These performance functions are used to review the influence of each random variable involved, especially the wave randomness in Makassar Strait. Wave randomness data for 59 years were obtained from SEAFINE. Furthermore, fatigue analysis was carried out on the data so that 59 annual fatigue damage random data were produced which were used as a function of load. In addition, the random variable of the load function which is also reviewed in the reliability analysis is the randomness of the stress analysis and the K parameters of the S-N curve. The structure is designed with a safety factor of 10 so that the reliability index can reach the target index recommended by Onoufriou (1999). Based on the results of the reliability analysis, the load random variable that have a large influence on the reliability index are the randomness of fatigue damage and the randomness of stress analysis. Then 1 performance function is selected which is recommended for calculating the reliability index. The reliability index of the braced monopod structure based on the performance function for the most critical joint is 3.62.