Withdrawal Resistance of Plain and Galvanized-Steel Nails During Changing Moisture Content Conditions

Plain and galvanized-steel nails were driven into Douglas-fir and red oak specimens which had been conditioned to 5 percent or 20 percent moisture content. Nail withdrawal resistance was measured after the specimens had been subjected to cycles of changing moisture content. Withdrawal resistance values were obtained immediately after nail emplacement and after 1, 2, 5, and 10 cycles of changing moisture content.. Total elapsed time for 10 cycles was 27 months. Although corrosion was immediate and extensive on both the plain and the galvanized-steel nails, average withdrawal resistance values at the end of the 10 exposure cycles were somewhat higher than values obtained upon withdrawal immediately after emplacement. The following conclusions were stated: 1) There is no significant difference in withdrawal resistance between nails having medium and blunt diamond points when the nails are subjected to a corrosive environment for a considerable period of time. 2) In general the relative magnitude, of withdrawal resistance of 6, 8, and 10 penny nails for a given nail type is unaffected by time. 3) There is an initial increase in withdrawal, resistance with time as nails corrode; the increase is dependent upon the wood species in which the nail is driven and nail type as well as time. This initial increase tapers off with time and will decrease as time continues. 4) Galvanized nails in Douglas-fir offer significantly higher withdrawal resistance than plain nails under the conditions imposed and during the time period covered by this experiment. 5) Plain nails in red oak offer significantly higher withdrawal resistance than galvanized nails under the conditions imposed and during the time period covered by this experiment. 6) Nails driven into Douglas-fir at a moisture content of 20 percent have higher withdrawal resistance than those driven at 5 percent. 7) Nails driven into red oak at a moisture content of 5 percent have higher withdrawal resistance than those driven at 20 percent. 8) The large and opposing species differences in nail withdrawal resistance indicate that increased precision in prediction of nail joint performance requires recognition of wood species as well as nail type and moisture content conditions. 9) The obvious severity of the cyclic conditions imposed in this study, resulting in extremely severe corrosion effects, is a normal circumstance in time-related, accelerated experiments and leads to difficulty in applying the experimental results to actual service situations. It is recommended that further investigation be conducted under more realistic time any exposure conditions.

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