Direct withdrawal strength of multi-staple joints in pine plywood

Although staple joints are common in the construction of upholstered furniture frames in plywood, little information is available about the additive effects of staples on the ultimate withdrawal strength of multi-staple joints constructed of this material. Withdrawal strength tests were carried out on 4-inch-wide, T-shaped, end-to-face, pine plywood joint specimens that were constructed with multiple 16-gage staples in order to evaluate these effects. Test results indicate that the number of staples positively affected the joint direct withdrawal strength. The withdrawal strength of multi-staple joints could be predicted knowing the withdrawal strength of single-staple joints and the multi-staple correction factor, and the withdrawal strength was found to be proportional to the number of staples raised to the 0.75 power. An average ultimate withdrawal strength of 1, 190 pounds can be obtained with five 16-gage staples driven into fastening members with a 1.25-inch penetration depth.