Numerical model for 3D steel moment frames with H-shaped beams and hollow-section columns under multi-directional seismic ground motions

Abstract In Japan, steel moment frames comprising H-shaped beams and square hollow-section columns with through diaphragms are often used for low- to middle-rise building structures. The column overdesign factor—strength ratio between columns and beams—is specified as ≥1.5 in Japanese seismic design code to ensure adequate energy absorption capacity against bidirectional ground motion by achieving an entire beam-hinging collapse mechanism. However, the required column overdesign factor of steel moment frames is obtained from analysis results conducted under unidirectional ground motions. Additionally, the numerical models of most previous studies considered the behavior of only beams and columns, and ignored the behavior of the panel zone of the beam–column connection. Nevertheless, the panel zone may yield with the beams and columns under severe earthquakes. In addition, the influence of panels on steel moment frames subjected to bidirectional ground motion is not completely understood, as a numerical model for panels under bidirectional shear forces and biaxial bending moments is yet to be proposed. Thus, this research proposes a novel numerical model for studying steel moment frames under multi-directional loadings to consider the 3D elastoplastic behavior of beams and columns, as well as panels. The proposed numerical model was validated by analyzing cruciform subassemblies of beams, columns, and panels, and the analysis results were compared to the experimental results from previous studies. Furthermore, a time-history response analysis was conducted for the 3D steel moment frames, and the energy dissipated from the plastic deformation of the beams, columns, and panels within each beam–column connection was discussed from the aspect of strength ratios between structural members.