Collapse Response and Design of Deep Steel Columns Subjected to Lateral Displacement

Recent experimental and computational studies have shown that the inelastic behavior of deep steel columns, where the cross-section depth is substantially greater than the flange width, is not yet well understood. To address this shortcoming, detailed finite element models that are validated using available experimental data, are used to study the response of deep steel columns subjected to combined axial and lateral loading. Two loading protocols are considered: (1) members that undergo monotonic lateral loading under a constant compressive force until failure (load then drift, i.e., LTD protocol); and (2) members that are subjected to various initial axial loads, displaced to a specified drift and then further loaded until failure (drift then load, i.e., DTL protocol). The loading protocols are designed to determine the effect that initial axial load, axial shortening, and local buckling effects play in predicting the failure mode and axial resistance of the member. Regression analysis is performed on the results to determine which parameters are most significant. The simulation studies show that global out-of-plane slenderness is a key parameter influencing behavior and that the effective buckling length of deep steel columns could be substantially greater than its initial value, a finding that has implications for seismic design.