Analytical Fragility Curves of Open Frame Platform Structures

Abstract

The seismic performance of open frame platform structures which is a complex structure commonly found in large oil refineries is evaluated in this study. Analytical Fragility curves are developed to evaluate the performance of each platform models at Immediate Occupancy damage state after an earthquake. The methodology that were used to develop the curves, are based on calculating axial deformation of the brace member using nonlinear time history analysis for different ground motions with different intensities and frequency contents. The fragility curves are developed based on the acceptance criteria for the brace member given from the FEMA 356. It was found that as the bracing member size increases within the same structural shape, the performance of the structure in reaching/exceeding immediate occupancy performance level decreases. Additionally, as the height of the structure increases the probability of reaching immediate occupancy increases. It was also found that certain structural members are not to be used as bracing members for these structures.