Roof Connections in Houses: Key to Wind Resistance

Chapter 7. Connections

“…A couple of studies (Reed, et al, 1996;Conner, et al, 1987) have investigated the capacity of roof-to-wall (i.e., sloped rafter to top plate) connections using conventional toenailing and other enhancements (i.e., strapping, brackets, gluing, etc.). Again, the primary concern is related to high wind conditions, such as experienced during Hurricane Andrew and other extreme wind events; refer to Chapter 1.…”

“…Based on the studies of roof-to-wall connections, five key findings are summarized as follows (Reed et al, 1996;Conner et al, 1987):…”

Lessons learned from analyzing tornado damage

“…As wind velocities increase with height above the ground, roof systems usually experience strong wind uplift pressures. Conner et al [1987] showed various illustrations in using straps and tie-downs in securing roofs to perimeter walls. Pull tests conducted by Canfield et al [1991] have shown a dramatic increase in the strength of the rafter-top plate connection when metal rafter ties were used instead of simple toe nailing.…”

Effect of building geometry on wind loads on low-rise buildings in a laboratory-simulated tornado with a high swirl ratio

“…Cheng also found that the allowable capacities (the average maximum load divided by a safety factor of 2.5) of all of the toe-nailed connections using nails were smaller than the required uplift loads of the model building codes ASCE 7-98, IBC 2000, and SSTD 10-99 for a 90 mph wind. Conner et al (1987) conducted tests on several different roof-to-wall connections and compared their capacities to the capacity of the conventional three 16d toe-nailed connection. They then calculated the wind speeds necessary to induce failure in these connections and compared them to the velocity frequency distributions of several different types of extreme wind events and found that with only small changes in the connection strengths would improve the connection performance to be able to resist the loading induced by almost all of the extreme wind events, including tornadoes (Conner et al, 1987).…”

“…Conner et al (1987) conducted tests on several different roof-to-wall connections and compared their capacities to the capacity of the conventional three 16d toe-nailed connection. They then calculated the wind speeds necessary to induce failure in these connections and compared them to the velocity frequency distributions of several different types of extreme wind events and found that with only small changes in the connection strengths would improve the connection performance to be able to resist the loading induced by almost all of the extreme wind events, including tornadoes (Conner et al, 1987). Canfield et al (1991) investigated the capacities of several types of roof-to-wall connections including toe-nailed connections with different types of nails, lag screw connections, and twelve different types of hurricane ties.…”