Module: Timber connections Unit: Dowel-type fasteners
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There are four criteria designers should take into account when selecting and detailing connections for a particular application: load transfer (stiffness, ductility, robustness and differential movement), appearance, fire resistance and durability.
The traditional mechanical fasteners for structural timber connections are divided into two groups depending on how they transfer the forces between the connected members – ‘dowel-types’ and ‘metal connectors’.
Metal fasteners have negligible fire resistance and absorb and transfer heat quickly. Where required, fire protection with plasterboard is the most common solution.
Metal fasteners are efficient but the relative weakness of the timber perpendicular to the grain remains the governing factor.
The most popular dowel-type fasteners are staples, nails, screws, bolts and dowels.
The most common nail is the round wire nail which is produced from a steel wire with a minimum tensile strength of 600 N/mm2 although twisted and annular shank nails have better pullout resistance than round nails.
Wood screws can be used for plain timber-to-timber joints.
Metal screws are often used for steel-to-timber and panel-to-timber joints.
The most common types of screws are countersunk head screw, round head screw and coach screw.
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