Performance-based design of reinforced concrete buildings subjected to seismic forces

Abstract

An approach for evaluating reinforced concrete crographics. structural frame systems subjected to seismic forces under the framework of performance-based design methodology was developed. The method integrates the design criteria according to the proposed 1997 NEHRP Recommended Provisions for Seismic Regulation for New Buildings & Other Structures (BSSC 1997), structural limit states, pushover analyses, various seismic hazard levels, non-linear time history dynamic analyses and structural fragility curves. Three performance levels (or limit states) consisting of immediate occupancy, life safety, and collapse prevention according to FEMA-273 (ATC 1997a) were considered. Monte Carlo simulation technique was used to model the variability of strength and stiffness involved in estimating the structural limit state capacities. Three different hazard levels representing standard frequent event (50% probability of exceedance in 50 years), design basis event (10% probability of exceedance in 50 years) and maximum considered event (2% probability of exceedance in 50 years) according to FEMA-273 (ATC 1997a) were used. The probabilistic nature of earthquakes was simulated by using 25 different records of measured time histories, from previous seismic events and scaled to various response spectra intensities (hazard levels). Inter-story was used as an indicative parameter for evaluating structural performance in form of structural fragility curves for the three limit states. The fragility curves developed in this study correlate the conditional probability of exceedance of the three structural performance limit states (BSSC 1997) to the three different seismic hazard levels prescribed by the FEMA-273 (ATC 1997a) and FEMA-274 (ATC l997b). Structural fragility curves can be used for establishing design criteria for new buildings, for evaluating the extent of damage incurred by a building under seismic demands and for comparing the performance of various structural systems.