The underside of a common nailhead is chamfered or tapered, unlike the flat head of a cooler nail. The compaction of the plywood underneath the nailhead, therefore, is more uniform for joints with cooler nail joints than joints with common 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.
OSB joints constructed with 7/16 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.
The average moisture content was 15.9 percent for the wood members in joints using 8d cooler nails (0.113 in shank diameter by 2-3/8 in long) and 10.3 percent for the wood members in joints using 8d common nails (0.131 in shank diameter by 2-1/2 in long).
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. Instead, the sheathing remained nailed to the wood member in these joints even though the sheathing around the nail was damaged.
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.
The stiffness of plywood joints with cooler nails increased with increasing nail-drive depth.
Plywood joints flush driven with common nails are approximately 11 percent stiffer than joints flush driven with cooler nails. Based on nail shank diameter, joints flush driven with common nails should be approximately 80 percent stiffer than joints flush driven with cooler nails, all other factors being equal.
(2006) determined the strength of plywood joints with overdriven sheathing by testing several joints constructed with 12 mm plywood sheathing attached to 38 by 89 mm wood members using 8d common or 8d cooler nails
. Four nail-drive depths were investigated using cooler nails
: flush, 1.6, 3.2, and 4.8 mm; common nails were all flush-driven.