Influence of Middle Member Thickness on Properties of Double-Shear Nail Joints

For three-member nail joints under double shear loading, the Canadian timber design standard specifies a minimum thickness of the middle member of eight times the diameter of the nail (8d). This requirement has created difficulties in the specification of midply shear wall because of the use of the relatively thin wood-based sheathing as middle member in the sheathing-to-lumber joints. The objective of this project was to evaluate if the European Yield Model adopted in the Canadian timber design standard can still provide acceptable prediction of strength and failure mode of double-shear nail joint that has middle member thickness less than 8d. Six groups of double-shear nail joints, covering two nail sizes and three sheathing thicknesses, were tested under both monotonic and reversed cyclic loads. Six parallel groups of single-shear nail joints were also tested. The effect of nail penetration into the point-side member was investigated through testing of two groups with different nail lengths with all other parameters being equal. The test results show that the European Yield Model can still be used to estimate the strength and failure mode of double-shear nail joints when the center member has a thickness much less than 8d. Therefore, a value of 2.5d is recommended on the basis of this test project. The nail penetration into the point-side member does not affect the strength of joints when the penetration length is more than 5d.