<span lang="EN-GB">Probabilistic Collapse Assessment of Reinforced Concrete Moment Frames Retrofitted with Buckling-Restrained Braces in Eccentric Configurations under Near-Fault Ground Motions

Existing reinforced concrete (RC) moment-resisting frames designed to pre-modern seismic codes often lack adequate lateral stiffness and ductility, rendering them vulnerable to collapse during strong earthquakes. While buckling-restrained braces (BRBs) are an efficient retrofit due to their stable hysteretic behavior, their application in eccentric configurations (E-BRB) to RC frames remains largely unexplored from a probabilistic collapse perspective. This study presents a seismic collapse evaluation of RC moment frames retrofitted with E-BRBs using the FEMA P۶۹۵ methodology. Three archetype buildings of ۴, ۸, and ۱۲ storeys were designed for two BRB lateral-force participation levels (۵۰% and ۱۰۰% of design base shear). Detailed nonlinear finite element models were developed in PERFORM-۳D, incorporating distributed plasticity, cyclic degradation, and P–Δ effects, and subjected to incremental dynamic analysis using ۲۷ near-fault ground motions (۱۴ pulse-like, ۱۳ non-pulse). Collapse fragility curves were generated, and the adjusted collapse margin ratio (ACMR) was compared against FEMA P۶۹۵ criteria. Results show that the E-BRB retrofit substantially enhances lateral stiffness, ductility, and collapse capacity. Under pulse-like motions, the median collapse spectral acceleration for the ۴-storey frame increased by ۸۸%, and the collapse probability at the Maximum Considered Earthquake level fell from over ۹۹% in the bare frame to negligible values. All retrofitted configurations satisfied FEMA P۶۹۵ requirements, with ACMR values two to three times acceptance thresholds. The system proved particularly effective against near-fault pulses, confirming its potential as a reliable, code-conforming retrofit strategy for RC buildings in high-seismicity regions.

کلیدواژه ها:

Buckling-restrained brace ، Eccentric configuration ، RC moment frame ، seismic retrofit ، FEMA P۶۹۵ ، Near-fault ground motion ، Probabilistic collapse assessment