Designing built-up columns? Now there’s a way to mechanically laminate multiple 2x members to meet the specifications in the National Design Specifications for wood. Simpson Strong-Tie evaluated Strong-Drive® SDW Truss-Ply screws for attaching multiple laminations with easier installation methods. With these screws, there’s no longer a need to nail from both sides of the column, or to use not-so-common 30d nails as specified in the NDS, or to pre-drill for bolts. Instead, installers can now install all the screws from one side of the built-up column, which provides time and cost savings.
In a previous blog post on soft-story retrofits, I briefly discussed beam bracing requirements for moment frames. This week, I wanted to go into more detail on the subject because it’s important to understand that a typical steel moment frame requires lateral beam bracing to develop its full moment capacity. Figure 1 below shows two common methods of beam bracing. While on the surface determining beam bracing requirements may not appear complicated, there are several items that could prove it to be more challenging than you might think, especially when steel moment frames are used in light frame construction.
Figure 1: Steel Beam Bracing
Before going into beam bracing in steel moment frames, it is important to discuss the behavior of a simply supported beam under gravity load. Short beams (Lb < Lp), might not require bracing to achieve the full plastic moment of the beam section. However, when a beam is long (Lb > Lr) and without bracing, the beam can twist or buckle out-of-plane. Figure 2 illustrates these two behaviors along with the case where the beam length is somewhere in between the two (e.g., Inelastic lateral torsional buckling). In addition, if beam sections are non-compact, flange local buckling (FLB) or web local buckling can occur prior to reaching the beams full plastic moment.