This study addresses a critical gap in seismic design by quantifying how plan asymmetry and multiple earthquake sequences interact to affect the nonlinear response of reinforced concrete (RC) frames. While earthquake-resistant design provisions have evolved, most current codes are based on single-event assumptions and simplified symmetry considerations, overlooking the cumulative effects of repeated ground motions observed in recent international studies.

In this research, symmetrical and asymmetrical low-rise RC frames are analyzed through nonlinear dynamic simulations, considering both single-event and multiple-event ground excitations for comparison. The analyses incorporate three-dimensional ground motions in horizontal and vertical directions, while explicitly modeling the nonlinear inelastic behavior of RC sections under severe seismic demands.

A dimensionless asymmetry ratio, defined by the relative distribution of stiffness and mass, is proposed to systematically evaluate torsional sensitivity in plan-irregular structures. Structural responses are further expressed through normalized indices, which enable consistent comparisons across different frame geometries and seismic scenarios.

The results show that increasing plan asymmetry amplifies inter-story drift, torsional rotations, and plastic hinge concentrations, particularly under successive earthquake sequences. These findings indicate that existing design provisions may underestimate the vulnerability of irregular RC buildings. This work is among the first to integrate plan asymmetry and multi-event seismic loading into a unified evaluation framework, offering a novel tool for refining earthquake-resistant design standards.