Buildings With Large Clearspan Wood Trusses
Using Post Frame To Ensure Structural Security
Figure 12: Truss resting on outer ply of a laminated post. Steel L-bracket placed on outer face of truss to help reinforce post-to-truss connection.
Component connections are critical to the structural integrity of a framing system. In buildings with large, clearspan wood trusses, the most critical connections are those between the truss and its supports. In addition to gravity-induced forces (a.k.a. bearing loads), these connections must resist shear forces acting perpendicular to the plane of the truss and uplift forces due to wind. Depending upon overall building design, the connections may also be required to transfer bending moment.
Wood posts enable the fabrication of strong, direct, yet inexpensive connections between large trusses and walls. Exact details for post-to-truss connections vary from designer to designer, and may be influenced by post type. Solid-sawn timber and glulam posts are generally notched to form a truss bearing surface. The truss is rested on the notches and bolted into place. A special plate/bracket like that shown in figure 12 may be added to increase connection load transfer capabilities. With mechanically-laminated posts, the truss may rest on a shortened outer-ply or on a shortened inner-ply. The later scenario, which is shown in figure 13, places the bolts in double shear and is a very effective connection.
Figure 13: When truss is sandwiched between outer plies of a mechanically-laminated post, bolts are placed in double-shear for a very effective connection.