Flush-driven common nail joints had a 32 percent reduction in strength compared to flush-driven cooler nail joints.
The compaction of the plywood underneath the nailhead, therefore, is more uniform for joints with cooler nail joints than joints with common nails.
Also, the additional chemical bonding between the cooler nail and wood may contribute to a slight increase in joint stiffness.
Reduction in displacement capacity due to overdriving is 38, 60, and 77 percent for cooler nail joints overdriven 1/16, 1/8, and 3/16 inch, respectively (compared to joints flush driven with cooler nails).
Plywood joints constructed with 15/32-inch plywood sheathing attached to 2 by 4 wood members using 8d common or 8d cooler nails were tested using the sequential phased displacement (SPD) loading protocol.
9 percent for the wood members in joints using 8d cooler nails (0.
Cooler nails were driven using a pneumatic nailing gun equipped with a nail stop to prevent overdriving the nails.
Further research is needed to validate this procedure, especially for joints with cooler nails because the strength is partly dependent on the thermal plastic resin.
A failure mode was not observed in seven joints tested with flush-driven 8d cooler nails.
Plywood joints overdriven 1/16 inch with 8d cooler nails experienced different modes of failure: nail tearing of plywood was observed in five joints; nail fatigue was observed in one joint; and no failure was observed in four joints.
Compared to joints with common nails, joints with cooler nails experienced considerably less nail fatigue.