Impact of Permanent Diagonal Bracing on Different MPC Wood Truss Types

Abstract

Some webs and interior compression chords of metal-plate-connected wood trusses require continuous lateral braces (CLBs) to reduce the effective buckling lengths of the members. The CLBs must also be braced, typically by permanent diagonal braces. The design of the CLBs and the companion diagonal braces is the responsibility of the building designer. This paper explains why some truss roofs without the required permanent diagonal bracing installed to stabilize the web CLBs perform better than engineering practices might predict. The results derived for a truss web requiring one CLB were contrasted to the general case of a long (interior) compression chord requiring many lateral braces. For the case of a long compression chord, it is especially critical that the builder designer specify the necessary permanent diagonal bracing needed to stabilize the CLBs, and moreover that the braces be installed. Motivation was given for using full sheathing as an alternate method for bracing interior compression chords, and it is suggested that a permanent bracing manual for wood trusses be developed and made available for practicing structural engineers.