Simplified Analytical/Mechanical Procedure for the Residual Capacity Assessment of Earthquake-Damaged Reinforced Concrete Frames

The series of recent catastrophic earthquakes worldwide have further emphasized the evident complexity and difficulty related to the evaluation of the post-earthquake seismic residual capacity of buildings. In the aftermath of a major seismic event, a fast, yet effective, safety evaluation procedure for earthquakedamaged buildings is critical to speed up and support the definition of emergency planning strategies, as well as to provide useful intel to the stakeholders and aid the decision-making process to enhance community resilience. Currently, state-of-the-art procedures for post-earthquake seismic assessment of buildings involve the use of non-linear static (pushover) analyses coupled with capacity reduction factors for plastic hinges’ response of damaged components, in terms of stiffness, strength, and ductility (e.g., FEMA 306). However, a standardized and easy-to-apply procedure, preferably analytical rather than numerical, that allows one to perform safety evaluation and loss assessment in either pre- and post-earthquake scenarios, has not been implemented yet. To achieve that goal, building on the recent developments at the international level, the analytical/mechanical SLaMA (Simple Lateral Mechanism Analysis) method, adopted by internationally recognized guidelines for the seismic assessment of existing buildings (NZSEE 2017) could be extended in order to develop a framework for pre- and post-earthquake safety evaluation and loss assessment of buildings. Therefore, this paper aims to investigate the possible implementations of a SLaMA-based procedure for the seismic assessment of damaged Reinforced Concrete (RC) frame buildings. The proposed procedure is based on the use of reduction factors for damaged structural members, in line with the FEMA 306 approach, and an update of the “hierarchy of strength” at the subassembly level when initial earthquake-related damage is considered. This way, the global force-displacement capacity curve of the structure in its either undamaged or damaged configuration can be evaluated. Finally, safety evaluation and loss assessment are carried out through simplified spectrum-based procedures, in terms of “Safety Index” (IS-V or %New Building Standard, %NBS) and Expected Annual Losses (EAL). An application of the SLaMA-based procedure is presented for a case-study building. By comparing the results of the undamaged and damaged configurations, higher seismic risk and economic losses are observed when cumulative damage is considered. The effectiveness of possible retrofit/repair interventions is also investigated. The proposed SLaMA-based procedure can be implemented within ad-hoc post-earthquake screening forms, supporting the decision-making process of both re-occupancy and repair/retrofit vs. demolition.