Effect of Drift Loading History on the Collapse Capacity of Deep Steel Columns

The use of deep wide flange steel columns is prevalent in seismic zones. However, their inelastic behavior, in general, and collapse capacity, in particular, under combined axial and lateral loading are not yet well understood. In order to address this shortcoming, the effect of drift loading history on the performance of deep columns subjected to various levels of constant axial force with different boundary conditions is investigated. Detailed finite element models that are validated using available experimental data are employed in this study. Three drift loading protocols are used: (1) symmetric cyclic loading, (2) asymmetric cyclic loading, and (3) monotonic loading. The drift loading histories are specifically selected to highlight key differences between idealized and realistic seismic demands as observed from complete frame analyses for collapse-susceptible first-story columns. The simulation results show that selecting a proper loading history is critical for assessing the collapse capacity of deep columns. The failure modes observed from the simulations are dominated by the global out-of-plane slenderness ratio, local slenderness ratio, and boundary conditions. The simulation results are used to assess the suitability of current design criteria.