Experimental Evaluation of Laterally Skewed Reduced Beam Section Moment Connections with and without Composite Concrete Slabs

Existing experimental reduced beam section (RBS) moment frame investigations, particularly those used for prequalification, consider orthogonally oriented beam-to-column connections. While the design commentary provided in current prequalification standards refers to recent skewed special moment frame (SMF) numerical studies and potential performance effects when a lateral beam skew is introduced, no experimental studies have been performed to verify the numerical findings. This study presents an experimental investigation into the cyclic behavior of RBS special moment frames that have lateral skew at the beam-to-column connection. Testing involves both bare-steel and composite skewed moment frame connections. In this study, a total of six single-sided bare-steel RBS connections having two column depths (W14× and W24×) and three skew angles (10°, 20°, and 30°) are considered, along with one composite double-sided RBS connection tested under two different beam bracing conditions (with and without beam bottom flange bracing outside the RBS). Experimental results indicate that current provisions for RBS SMF design can be applied to laterally skewed configurations; however, it is recommended that beam lateral bracing be included within d/2 from the end of the RBS for all connections having beam skews greater than 10°, even if a composite concrete slab is included. Column torsional bracing should be included near the bottom of the beam-to-column connection for medium and deep columns (W24× or deeper) having beam skews greater than 20°. Shallow (W14×) columns having beam bracing at d/2 from the RBS performed satisfactorily (based on current prequalification requirements) at skews up to 30°. Medium (W24×) columns having beam bracing at d/2 from the RBS performed satisfactorily at skews up to 20°, with no observable column flange yielding and moderate column twist. The W24× column configuration at 30° skew also performed satisfactorily based on prequalification requirements; however, the extent of observed column twisting raises stability concerns.