Damage Analysis of Steel Concentrically Braced Frame Systems under Seismic Conditions

The overall objective of this research is to understand the potential for earthquake-induced damage of the steel self-centering concentrically braced frame (SC-CBF) system and compare this damage potential with the damage potential for the conventional special concentrically braced frame (SCBF) system. The SC-CBF system is a new seismic lateral force resisting system (SLFRS) that was developed and studied at ATLSS Engineering Research Center at Lehigh University. Extensive analytical simulations and experimental hybrid simulations were conducted on a 60% scale 4-story SC-CBF system using the Network for Earthquake Engineering Simulation (NEES) facility located at the ATLSS center. While the SC-CBF system was damage free under the ground motions at the DBE hazard level and self-centered under the ground motions at the MCE hazard level, the potential for damage of the SC-CBF system at hazard intensities beyond MCE had not been studied. The scope of this research includes: (i) collapse performance evaluation of the SC-CBF and conventional SCBF in accordance with FEMA P695; (ii) development of a probabilistic seismic damage analysis framework considering damage states other than building collapse; (iii) including system parameter variability and modeling uncertainty in the probabilistic damage analysis framework; and (iv) developing and comparing damage scenario fragilities for the innovative SC-CBF and conventional SCBF systems.;Collapse performance evaluations for the innovative SC-CBF system and the conventional SCBF system were conducted in accordance with FEMA P695. It was observed that the margin against collapse for the SC-CBF system is greater than the margin against collapse for the SCBF system. Residual drift for the SC-CBF system is observed at relatively large hazard intensity levels compared to the SCBF system.;A probabilistic seismic damage analysis framework was developed for buildings using the event tree diagram concept. Damage states other than the collapse of the building were considered in developing the probabilistic seismic damage analysis framework. In the framework, damage assessments are performed at the system level, subsystem level, and component level. Damage scenarios are defined using the three levels of damage assessments.;System parameter variability and modeling uncertainty were included in the probabilistic seismic damage analysis framework using results from Monte Carlo simulation. An approximate method for including the system parameter variability and modeling uncertainty in the damage scenario probabilities was developed and presented.;Fragilities were developed for different damage scenarios for the SCBF and SC-CBF systems using the probabilistic seismic damage analysis framework. Damage scenario fragilities were compared for the SCBF and SC-CBF archetype buildings. It was observed that the SC-CBF system has a smaller probability of collapse than the SCBF system, and has smaller probability of structural damage (when collapse has not occurred) than the SCBF system.