Withdrawal resistance of ring-shank nails embedded in Southern pine lumber

Abstract

The overall goal of this research was to was to gain a better understanding of ringshank nail connections, and to critically evaluate allowable design values for withdrawal. Specific goals ]Included: 1) measuring and comparing withdrawal resistances of ring-shank nails embedded in Southern pine lumber, 2) identifying candidate probability distributions for the withdrawal data, 3) critically evaluating currently published design values for withdrawal resistance of ring-shank nails, and 4) examining the failure mode of nail head pull-through. Withdrawal resistances were measured for 3.76 mm (0. 148 in.), 4.50 mm (0. 177 in.), and 5.26 mm (0.207 in.) diameter galvanized and ungalvanized ring-shank nails from two different manufacturers embedded in Southern pine lumber. Data were statistically evaluated to determine the effects of threading and galvanization on withdrawal resistance. Results indicated that the threading process and galvanization had significant effects on withdrawal resistance. The mean withdrawal values for the 3.76 mm (0. 148 in.) bright and galvanized were, respectively, 64 N/mm (367 lb/in.) and 60 N/mm (343 lb/in.). The means for the 4.50 mm (0. 177 in.) bright and galvanized nails were 76 N/mm (434 lb/in.) and 69 N/mm (396 lb/in.). The mean for the 5.26 mm (0.207 In.) nails was 83 N/mm (474 lb/in.). Coefficients of variation ranged from 0.226 to 0.269. The Welbull and lognormal were the best-fitting probability distributions for the withdrawal data. Current allowable design values were critically evaluated. If the current method of dividing the mean ultimate resistance by a factor of five to obtain design values were used, an increase of 26% to 29% over current design values was noticed. Using the method of 5% parametric tolerance limit, values increased over 50% compared to current design values. Ring-shank nails were found to have approximately twice the withdrawal resistance of smooth-shank nails of the same diameter. ,Although head pull-through was found to have a slight effect on mean ultimate connection strength, the left tall of the strength distribution was not affected. From a design standpoint, head pull-through was not as significant. Current design values appeared to be conservative. Further research is needed on a variety of lumber species and nail sizes.