Finite Element Study of Seismic Compactness Limits for Tubular Columns in Seismic Frames

Current local seismic compactness limits specified in the American Institute of Steel Construction Seismic Provisions (AISC 341-22) for hollow structural section column members are extrapolated from uniaxial tests of hollow structural sections braces, where the developed plastic hinge is concentrated over a short length at the center of the member. This behavior is very different than the behavior observed in a first story column of a seismic moment frame. To address this difference and explore the behavior of hollow structural section columns in moment frame systems, detailed finite element models of square hollow structural sections are validated to ensure their accuracy under combined large axial loads and cyclic bending moments. These models are then used to explore the influence of different axial load ratios and local slenderness values that cover a range of design parameters for square hollow structural sections. The constant applied axial loads range from 20% to 40% of the column yield strength. The lateral loading protocol is representative of a far-field type earthquake. The performance of these columns is evaluated with regards to maximum moment capacity, moment capacity degradation with continued cycling and rotational capacity. The results will provide a means of developing a rational set of seismic compactness limits for highly ductile hollow structural section columns used in seismic moment frames in the future.