Earthquakes have repeatedly demonstrated their capacity to cause severe damage to reinforced concrete buildings, particularly those with structural irregularities in plan, elevation, or mass distribution. Such buildings exhibit complex seismic responses including torsional coupling, stress concentrations, and non-uniform deformations that conventional elastic analysis methods cannot accurately capture. Despite these well-recognized challenges, irregular configurations remain widespread in practice due to architectural and functional demands, making their reliable seismic evaluation a critical concern in earthquake engineering. This paper presents a comprehensive review of seismic behavior and performance assessment of irregular RC buildings, covering classification of structural irregularities, development of nonlinear analysis techniques including pushover methods, and evolution of performance-based seismic design frameworks guided by FEMA, ATC, and ASCE standards. Reviewed studies consistently indicate that linear methods underestimate seismic demand by margins of 15–40%, while nonlinear analysis provides significantly more reliable performance assessment. Key research gaps are identified, suggesting directions for future investigation into advanced evaluation methods for irregular RC structures.

Keywords— Structural Irregularity; Seismic Performance; Reinforced Concrete Buildings; Nonlinear Analysis; Performance-Based Seismic Design; Pushover Analysis.