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### Pressed Drift Pin Bolts in Wood Force Formulae and Calculator.

Wood Pressed Drift Pins / Bolts Pullout Withdraw Resistance Force Formulae and Calculator

A drift bolt (or drift pin) is a long pin of iron or steel, with or without head or point. It is driven into a bored hole through one timber and into an adjacent one, to prevent the separation of the timbers connected and to transmit lateral load. The hole in the second member is drilled sufficiently deep to prevent the pin from hitting the bottom.

The ultimate withdrawal load of a round drift bolt or pin from the side grain of seasoned wood is given by seasoned wood may be expressed as:

p = 45.51 G2 D L (Metric screws)

p = 6,600 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 = shank diameter of the screw (mm, in.),
L = Length of penetration of the threaded part of the screw (mm, in.).

This equation provides an average relationship for all species, and the withdrawal load for some species may be above or below the equation values. It also presumes that the bolts are driven into prebored holes having a diameter 3.2 mm (1/8 in.) less than the bolt diameter.

Data are not available on lateral resistance of drift bolts. The yield model should provide lateral strength prediction, but the model has not been experimentally verified for drift bolts. Designers have used bolt data and design methods based on experience. This suggests that the load for a drift bolt driven into the side grain of wood should not exceed, and ordinarily should be taken as less than, that for a bolt of the same diameter. Bolt design values are based on the thickness of the main member in a joint. Thus the depth of penetration of the drift bolt must be greater than or equal to the mainmember thickness on which the bolt design value is based. However, the drift bolt should not fully penetrate its joint.

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References:

• AF&PA. 1997. National design specification for wood construction. Washington, DC: American Forest & Paper Association.
• ASCE. 1995. Standard for load and resistance factor design (LRFD) for engineered wood construction. Washington, DC:
• American Society of Civil Engineers. ASCE. 1996. Mechanical connections in wood structures. Washington, DC: American Society of Civil Engineers.