Probabilistic seismic assessment of tall RC core-wall systems featuring different coupling beams under short- and long-period ground motions

High-rise reinforced concrete (RC) frame-core buildings are highly susceptible to long-period ground motions due to resonance effects. This study performs a probabilistic seismic fragility assessment of such systems, explicitly addressing uncertainties associated with structural height and earthquake frequency content. Nine analytical models, representing 15-, 25-, and 35-story buildings with identical floor plans, were developed using Perform-3D. Each height group incorporated three coupling beam configurations: reinforced concrete, typical steel, and replaceable steel coupling beams. Nonlinear dynamic analyses were performed through Incremental Dynamic Analysis (IDA) using 22 ground-motion records representing short- and long-period characteristics. Fragility functions were derived for four HAZUS-based damage states. The results reveal a significant increase in vulnerability under long-period excitations, particularly for taller buildings. Systems with replaceable steel coupling beams exhibited 27% and 12% higher median fragility compared to RC and typical steel coupling beams, respectively, under complete damage, while achieving 17% and 11% greater seismic energy dissipation. These findings underscore the importance of coupling beam configuration in enhancing resilience and energy dissipation capacity. The study establishes a comprehensive yet concise probabilistic framework for assessing and comparing the seismic performance of tall RC frame-core buildings under varying frequency contents and height-dependent uncertainties.