Seismic performance of fixed offshore structures under far field earthquake

Abstract

Malaysia is located at a very low seismic activity area but the active earthquake fault line is through the centre of Sumatran, Indonesia which lies just approximately 350km from Peninsular Malaysia. The earthquake that occurs in Indonesia was due to the strike-slip fault that has affected the building structure in Malaysia. It happens because of the amplification process generated from the source of the event. The aim of this study was to evaluate performance and vulnerability of offshore structures using real peak ground acceleration. Between 2004 and 2012, a few interpolate earthquake events with magnitudes of Mw = 3.5 were recorded. These data were provided by Malaysia Meteorological Department Malaysia (MMD) and 10 of the events were shallow strikeslip events. The earthquake Off West Coast of Sumatra that happened on 26th December 2004 has been selected as the biggest earthquake event in the Malaysia region during that time. By using regression analysis, attenuation function that has been developed and the value of maximum ground acceleration that hit offshore platform was identified. Using the real peak ground acceleration, vulnerability and performance of 5 models of typical offshore platforms were evaluated. The typical fixed offshore platform was analysed by using SAP 2000 finite element software. Time history analysis and pushover analysis were done on the models in which the results were compared to the resistance value itself and the performance indicator produced by FEMA-365. The offshore structure was analysed by several steps in pushover in terms of x-direction and y-direction and some parts of the structure were classified as Immediate Occupancy (IO), Life Safety (LS), and Collapse Prevention (CP) level of performance. Moreover, the results retrieved from the real scale analysis were compared to the experimental work that employed the harmonic shaking table machine. In conclusion, the findings contribute to the seismic performance of offshore platforms in Malaysia. It proves that the offshore platforms in the country is very well sustained with a high-end performance.