Integrated Probabilistic Seismic Assessment of Steel Diagrid High‐Rise Structures With Vertical Irregularities

ABSTRACT This study conducts a probabilistic seismic assessment of steel diagrid high‐rise structures with vertical irregularities, evaluating 18‐ and 24‐story configurations—including fully regular (Model A), fully stepped‐back irregular (Model B), and hybrid stepped‐back layouts (Model C)—under near‐fault ground motions. Finite element models, designed according to the Iranian National Building Code (INBC) and Standard No. 2800, were analyzed using Incremental Dynamic Analysis (IDA). Key metrics such as interstory drift and stiffness degradation were tracked to characterize nonlinear behavior, with lognormal fragility curves calibrated via maximum likelihood estimation (MLE). Results reveal that building height and plan irregularities critically influence seismic performance: regular 24‐story configurations demonstrated 15%–20% lower drift responses and higher collapse capacities than irregular counterparts, while 18‐story structures exhibited superior dynamic resilience. Notably, slab removal and setbacks amplified vulnerability under high‐intensity shaking. These findings underscore the necessity of maintaining diagrid continuity at setbacks and redistributing lateral stiffness to enhance seismic resilience in irregular high‐rise systems.