The web member is one of three key components to any truss. In additional to the top and bottom chords, webs typically carry axial forces to the chords that eventually pass to the truss bearings. The vast majority of trusses utilize 2x4 dimensional lumber but webs can vary from 2x3 up to 2x12 lumber depending on the design. The grade and species of lumber used for webs is typically different from the chords of the truss to drive economic efficiency. Factors that impact the size of web members include on-center spacing, dead and live loads applied to the truss, span, and pitch, among others.
In floor truss applications, 2x3 or 2x4 material is used to cut webs. When oriented on the flat face of the board, webs will be cut with bevels on each end to create more surface area at the joint for a better fit. In some instances, square cut floor webs can be used but result in larger plates at the joint. Floor trusses oriented in a 4x2 or 3x2 manner are much more stable than floor trusses oriented on edge, allowing installers the ability to easily walk across members without tipping or rolling the trusses during installation while floor decking and bracing is applied.
Webs are typically cut with many angles on each end to allow for a tight fit at the joint. Sophisticated automated computer-driven saws are used to cut webs and other truss parts with very specific angles and lengths that allow for intricate joints and increased surface areas to aid in the transfer of forces. Linear saws are able to quickly cut differing webs out of one piece of lumber thereby minimizing waste. Component saws are utilized to cut high volumes of webs of the same configuration out of a fixed length board using 5 or 6 saw heads. Pull saws, either manual or semi-automated, are used to cut a variety of parts including webs in low quantities. Common trusses are typically designed with symmetrical webs to reduce the number of saw setups and make the overall truss fabrication process less complicated.
Often web members in compression require continuous lateral restraints (CLR) to prevent buckling under the applied design loads. Webs requiring CLRs will be denoted on the Truss Design Drawing with a rectangle with an “X” through it or a rectangle fully blackened on the web. CLRs attached to similar adjacent trusses are required to have a diagonal brace to transfer the forces from the CLR into a lateral force resisting system such as the roof or ceiling sheathing. Alternatively to CLRs, individual web restraints such as scab, “T,” or “L” reinforcements can be installed in the field on the truss in instances where a CLR is not possible due to differences in web patterns of adjacent trusses. Another alternative to field applied restraints are factory installed stacked webs and proprietary metal reinforcements that have been specially designed for this purpose.
For more information on web member restraints and temporary and permanent truss bracing in general, refer to BCSI.