Development of the Energy Method in the Fragility of Steel Moment Frames Designed Using Energy-Based Performance-Based Design

This study investigates and compares the seismic performance and fragility of steel moment-resisting frame structures designed using two methods: the energy-based performance approach and the conventional force-based method. The fragility of each structure was calculated through two approaches: the conventional method (based on maximum story drift) and the method based on dissipated plastic strain energy in the structure. To do so, three steel moment frame structures including 4, 8, and 12 stories were designed using both the force-based method and the energy-based performance design method, and their seismic performance was compared. Energy-based fragility curves for these structures were developed by first determining the allowable strain energy at performance levels corresponding to boundary conditions. Then, energy-based fragility curves for three performance levels (elastic, life safety (LS), and collapse prevention (CP)) were computed and compared with the conventional method. The results indicate that the exceedance probability in the energy method and the conventional method align more closely at the CP performance level compared to the LS level. However, when the energy-based fragility assessment is applied to energy-designed structures, the fragility results at the CP level for the 4- and 12-story structures closely match those obtained when the fragility of the force-based design structure is calculated based on maximum story drift.