Table 3.2. Section Properties of the Studied Column SectionsIn addition, the effect of lateral bracing on the connection assembly performance was also investigated by introducing actual lateral supports from transverse beams and the concrete with metal deck floor that exists in almost all steel framed buildings. To study bracing effects of the floor slab, in some analytical cases, the beam was laterally braced along the beam top flange outside the RBS. Two different boundary condition cases were considered: (1) Unbraced case – where the beam had no lateral restraints similar to specimens tested by Gilton et al (2000); and (2)
Use of Deep Columns in Special Steel Moment Frames, J. Shen, A. Astaneh-Asl and D. B. McCallen, 2002. 24Braced case – where the beam was laterally restrained in its panel zone and top flange except in the RBS region. For comparison, an additional beam-to-column connection with a non-compact beam section, W30x90, and a W27x194 column, was also included in this study. The cyclic analyses applied a maximum displacement of 6% story drift ratio in the same manner as conducting a physical test per FEMA-350 (2001). The following sections will present a summary of the analytical results together with discussions of various issues. 3.3.1. Overall Cyclic Behavior of Deep Column Connections Figures 3.7, 3.8, and 3.9 show the cyclic behavior of the connection assemblies with W30x191, W33x169, and W201x201, respectively. The cyclic loops of the connections demonstrated that the connections with deeper columns were stable. With lateral bracing (the solid-blue lines in the figures), the connections did not have any significant strength reduction before the 4% drift ratio. Under the cyclic loading, the strength degradation occurred upon the Figure 3.7. Cyclic Behavior of the Connection with W30x191 Column and W36x150 Beam.
Use of Deep Columns in Special Steel Moment Frames, J. Shen, A. Astaneh-Asl and D. B. McCallen, 2002. 25load reversal in both positive and negative deformation regions after the plastic hinge formed in the RBS region at about 3% drift ratio, mainly due to inelastic local web and flange buckling. Without lateral bracing (the dashed-red lines in Figures 3.7, 3.8, and 3.9), the connections experienced column twisting and beam lateral torsional buckling after 4% drift ratio, demonstrating a larger strength reduction than those with lateral bracing. It seems apparent that the lateral supports to the beam flange under compression improved the inelastic behavior of connections with deep columns. In particular, the post-buckling strength degradation was reduced considerably by lateral supports provided by the floor, as shown in Figures 3.7, 3.8, and 3.9. The lateral supports to the beam prevented lateral movement of plastic hinge area and extended the deformation prior to the onset of strength degradation. The local buckling of the flanges and web was mainly responsible for a slow degradation in strength at a later deformation stage for the braced connections. A larger strength degradation under negative bending moment, when the beam top flange was in tension, in the above figures indicates that extra lateral supports to the bottom flange can help to enhance inelastic cyclic behavior. Note that