Stability Requirements of Deep Steel Wide-Flange Columns under Cyclic Loading

Just recently, valuable experimental data that characterized the hysteretic behavior of deep wide-flange steel columns (i.e., column depth, d >16 inches) at full-scale became available. Such members are typically used in steel moment-resisting frames (MRFs) in North America. In order to expand the findings of the experimental program, an extensive parametric study is conducted using a validated continuum finite element (FE) modeling approach. The nonlinear behavior of more than 40 steel wide-flange cross-sections is investigated. Each steel column is subjected to a monotonic, a symmetric cyclic, and a collapse-consistent lateral loading protocol coupled with different levels of constant compressive axial load ratios. Based on the FE results, the cyclic deterioration in the column flexural strength and stiffness is evaluated. Accordingly, design recommendations are developed related to the seismic compactness criteria for highly ductile members such that column axial shortening can be reduced under design basis and low-probability of occurrence earthquakes. The range of out-of-plane force demands is also evaluated for the lateral bracing design of columns in steel MRFs. In that respect, the current AISC provisions are evaluated. Empirical equations are developed for predicting the out-of-plane force demands and the plastic hinge length in steel wide flange columns.