Bracing for load-bearing framing to resist racking under wind and seismic loads
Diagonal tension strapping and gusset plate components are used in combination to provide shearwall (racking restraint) for light-gauge load- bearing framing under wind and seismic loads. They are normally installed on both sides of the wall directly over framing members and are easily covered with facing materials. Straps are positioned diagonally from the bottom track to the top track. In order to resist load in each direction, an X-configuration should be used. At a minimum, double studs are positioned at ends of the X-brace to serve as compression studs.
Straps are either attached directly to the compression studs or are attached via Gusset Plates. Compression studs must be anchored to the foundation, normally with ClarkDietrich Holdowns. For multi-story construction, the uplift loads are extremely high. It is not uncommon to require 20,000 to 40,000 pounds of uplift force at these connections. Since ClarkDietrich Holdowns are not designed to resist this magnitude of force, it is recommended that embedded plates be installed prior to pouring the concrete foundation. A heavy steel assembly is then welded to the embedded plate and to the compression studs.
Caution: Racking loads are first transferred to the roof or floor decking and then to the shearwalls (X-bracing). The X-bracing then relies on a proper foundation to resist uplift and shear forces. In order for the system to function properly, the load path from the roof or floor deck to the shearwalls to the foundation must be complete. This normally requires additional bracing, blocking, track and rim splices, drag struts, uplift anchors and heavy-duty foundations.
- Strapping is available in flat lengths and coil form.
- Available widths are 2”, 4”, 6”, 8”, 10” and 12”.
- Gauges: 20 (33 mils), 18 (43 mils), 16 (54 mils), 14 (68 mils) and 12 (97 mils).
- Standard gusset plate sizes are 6”x 6”, 6”x 12” and 12”x 12”.