Experimental and Numerical Evaluation of Steel Columns for Performance-Based Seismic Assessment of Steel Moment Frames

This paper summarizes the findings of a long term experimental program corroborated with detailed finite element simulations that investigated the hysteretic behavior of wide-flange columns in steel moment-resisting frames (MRFs) designed in highly seismic regions. Several aspects of the steel column behavior are thoroughly investigated. It is shown that steel column axial shortening is a failure mode that strongly influences the steel column stability under earthquake-induced loading. The amount of axial shortening can be considerably different in interior columns compared to end (exterior) columns that experience transient axial load demands due to dynamic overturning effects. Axial shortening is typically followed by column out-of-plane deformations that become maximum near the dissipative plastic hinge zone and migrate near the column top end. This failure mode is strongly influenced by the considered column end boundary conditions. Routinely used symmetric loading histories provide insufficient information for modeling the cyclic deterioration in flexural strength and stiffness of steel columns near collapse. Modeling recommendations for updated backbone parameters for nonlinear modeling of steel columns are proposed inline with the current ASCE 41 nonlinear modeling recommendations for performance-based seismic assessment of steel moment frames.