Fragility Analysis of Fixed Offshore Platform in Malaysia Under Earthquake Effect

Abstract

Abstract In Malaysia, the oil and gas industry contribute significantly to its economy over the past decades. Currently there are over 250 offshore platforms in Malaysian waters. These platforms may be vulnerable to earthquake effects coming from near and far fields since seismic loading was not considered during the design stage for all offshore structures within all three (3) offshore sectors in Malaysia waters, including Sabah. Contrary to common belief that Malaysia is located outside the Pacific Ring of Fire of recent incidents and research is proving the opposite. In this study, seismic vulnerability assessment for fixed offshore platform in Sabah water is performed. Non-linear static (Pushover Analysis) and non-linear dynamic analysis (Incremental Dynamic Analysis or IDA) were performed prior to obtaining the fragility curve. Pushover analysis shows the seismic capacity through determining the drift ratio of the structure. The outcome of the analysis will then be classified into different damage levels according to Federal Emergency Management Agency (FEMA) categories; Operational Procedure (OP), Immediate Occupancy (IO), Damage Collapse (DC), Life Safety (LS) and Collapse Prevention (CP). Incremental dynamic analysis was performed by series of non-linear response histories which enabled PGA values to be systematically scaled. The maximum displacement and drift ratio were computed and compared with the drift ratio from pushover analysis to be classified into FEMA defined damage levels. Then, the mean and standard deviation of the PGA values were computed and substituted into fragility curve equation. The curve describes the probability of damage of the fixed offshore platform under earthquake effects. From the result, the vulnerability of the fixed offshore platform in Sabah water for an earthquake was concluded to be having a low probability of damage, i.e., 6.4% OP and 4.86% IO associated to Sabah PGA value of 0.28g.