Nonlinear Higher-Mode Effects in Torsionally Coupled Low-Rise Buildings

Higher-mode effects in low-rise buildings exhibiting coupled lateral-torsional behavior can significantly influence seismic response and should be properly reflected in the seismic design procedure. Conventional criteria for identifying higher-mode-dominated response are generally based on elastic response spectrum analysis, which limits their direct application to inelastic structures. This study investigated the influence of structural nonlinearity on higher-mode effects in torsionally coupled low-rise buildings through nonlinear static and nonlinear time-history analyses. Existing elastic-analysis-based higher-mode indicators were evaluated through a comparison with the higher-mode effects observed in nonlinear response. Higher-mode-effects generally decreased with an increase in structural nonlinearity, whereas some structures considered in this study exhibited nonlinear higher-mode effects greater than those estimated in the elastic state. These findings provide insights into the limitations of directly applying elastic higher-mode indicators to nonlinear torsionally coupled structures and can serve as bases for developing assessment approaches that account for nonlinear response characteristics.