Comparison of Lag Screws and Threaded Nails in a Typical Structural Joint

Standard lag screws were compared with annular threaded nails (regular and hardened) in a typical laminated southern yellow pine hanger-connected joint (purlin-to-arch). Twenty pairs of joints were tested; in each pair, one was fastened with lag screws, the other with either regular or hardened nails. Companion tests were also conducted qn individual fasteners in direct withdrawal and in shear (“lateral resistance”). Results of the tests of fasteners showed that lag screws had double the withdrawal resistance of nails. In maximum shear resistance regular nails were equal to lag screws and hardened nails clearly superior. In joint tests, although load was applied laterally, bending of fastener shanks introduced a component of withdrawal load, and thus lag screws had a slight edge over regular nails. Because of their greater resistance to bending, the hardened nails provided stronger joints than those made with lag screws. Since distortion of the hanger made the hanger the limiting factor, however, the full potential of the hardened nails was probably not realized.

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