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### Wood Nail Pullout Withdraw Resistance Force Formulae and Calculator

Wood Nail Pullout Withdraw Resistance Force Formulae and Calculator

Various types of nails: (left to right) bright
smooth wire nail, cement coated, zinc-coated, annularly
barbed, and barbed.

The resistance of a nail shank to direct withdrawal from a piece of wood depends on the density of the wood, the diameter of the nail, and the depth of penetration. The surface condition of the nail at the time of driving also influences the initial withdrawal resistance.

For bright common wire nails driven into the side grain of seasoned wood or unseasoned wood that remains wet, the results of many tests have shown that the maximum withdrawal load is given by the empirical equation

p = 54.12 G2 D L (Metric screws)

p = 7,850 G2 D L ( inch-lbs)

Where:

p = Maximum withdrawal load (N, lb),
G = Specific gravity based on ovendry weight and volume at 12% moisture content,
D = Ddiameter of the nail (mm, in.),
L = Length of penetration of the nail into the wood (mm, in.).

The loads expressed by the above Equation represent average data. Certain wood species give test values that are somewhat greater or less than the equation values. A typical load– displacement curve for nail withdrawal (Fig. A) shows that maximum load occurs at relatively small values of displacement.