Withdrawal strength of threaded nails

Threaded nails are used in wood construction because of their superior perf ormance, but relatively few tests have been conducted on nails larger than 12d (3.76 mm diameter). Experience has suggested that threaded nail withdra wal design values are too conservative. The Forest Products Laboratory and Washington State University have been cooperatively characterizing the stre ngth of threaded nails over a range of wood species and nail types. This pa per focuses on the immediate withdrawal strength of annularly threaded nail s in Douglas Fir and Spruce-Pine-Fir, helically threaded nails in Southern Pine, and smooth nails in Southern Pine and Spruce-Pine-Fir lumber. Average withdrawal strength of threaded nails was greater than that of smooth shan k nails of the same diameter. In comparison of experimental withdrawal stre ngth to existing design procedures for assigning allowable withdrawal stren gth design values, annular shank nails showed thr greatest difference. With drawal strengths of nails from five different manufacturers were not signif icantly different. Comparisons of the effect of galvanizing on withdrawal s trength were inconclusive.