Dynamic stability of deep and slender wide-flange steel columns - Full scale experiments

In North America, a common design practice for steel frame buildings with perimeter steel special moment frames (SMFs) is to employ deep and slender wide-flange steel columns (i.e., range of column depth, d > 16 inches). Till recently, very little was known regarding the hysteretic behavior of such members because of lack of available experimental data. This paper discusses selective findings from a full-scale testing program that was conducted at Ecole Polytechnique Montreal with the use of a 6-degree-of-freedom experimental setup. The testing program investigated the cyclic behavior of 10 full-scale beam-columns. The specimens had a depth of 24 inches (i.e., W24xl46 and W24x84 cross-sections) and were subjected under various lateral-loading protocols coupled with constant compressive axial load. The boundary conditions of the specimens simulated a fixed support at the column base and a flexible boundary at the column top end to mimic the flexibility of a beam-to-column connection at the floor level. The tested specimens represented typical interior first-story columns in mid-rise steel SMFs. This paper summarizes the main observations related to the effect of local and global slenderness ratios on the cyclic behavior of beam-columns. The effect of bidirectional lateral loading on the dynamic stability of beam-columns is also addressed. Observations related to the effect of the employed loading history as well as the lateral bracing force design requirements on steel wide- flange beam-columns are also provided based on the available experimental results.