Key Factors that Affect the Behavior of Steel Beams and Columns in Special Moment Frames

Abstract

Steel Special Moment Frames (SMFs) are favored seismic force-resisting systems due to their architectural flexibility and high ductility. While shallow columns (section depth less than 356 mm) were commonly used in these systems before the Northridge earthquake, deeper columns (section depth greater than 356 mm) have become more popular in recent years to meet code-enforced story drift requirements economically. However, limited research exists on the hinging behavior of deep columns under axial compression and cyclic drift. Since deep columns exhibit larger slenderness ratios and are more susceptible to local and global buckling, understanding their behavior is crucial. This study investigates the behavior of fifteen four-story steel SMFs using finite element program simulations, focusing on four key factors affecting frame behavior: 1) Column bracing, 2) Beam bracing, 3) Column stiffening, and 4) Strong Column Weak Beam (SCWB) ratio. The influence of axial force level and column section properties is also examined. Results demonstrate that deep columns may experience local and/or global instabilities at relatively low story drift levels. Findings suggest that SMF performance can be enhanced by bracing deep columns at the top and bottom levels of beam flanges and adding stiffeners to the columns' web. Controlling column shortening by increasing the SCWB ratio is also recommended.