Effect of Bracing and Anchor Choice on the Strength of Metal Plate–Connected Wood-Truss Assemblies Carrying Fall-Arrest Loads

AbstractFalls from roofs in residential construction can cause catastrophic injuries with severe consequences. Ensuring that personal fall-arrest system anchors are attached securely to the building with a clearly defined load path is important. In this article, the authors measured the load capacity of a series of five metal plate–connected wood trusses in a roof system using various top chord bracing elements and different fall-arrest anchors. The different types of top chord bracing included wood bracing installed between the joists, wood bracing installed on top of the joists, and a proprietary engineered steel brace. The fall-arrest anchors tested included a stanchion type anchor, a cross-arm strap, and a spreader bar attached to three trusses. Load and displacement of the truss assemblies were monitored continually throughout testing. The in-between bracing performed well because of the compression of the trusses, which created a pinching force on the brace that prevented fastener withdrawal. The three-truss anchor performed well by maintaining the strength of the wood system. The addition of sway bracing and additional top chord bracing located near the cross-arm strap created an anchor strong enough to meet Occupational Safety and Health Administration (OSHA) regulations. Sway bracing is recommended as an effective way to tie the truss structure together because it creates a greater distribution of load through the truss members. Proper bracing of the structure is essential for providing adequate support to fall-arrest anchors.