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(b) Annular ringed (c) Helical threaded

Nailed connections are simple to form and are suitable for lightly loaded structures and where connections are formed from relatively thin members. They are commonly used in framing, walls, decks, floors and roofs and in nearly every construction that involves light loads and simple elements.

The performance of a nail, both under lateral and withdrawal loading, may be enhanced by mechanically deforming the nail shank to form annular ringed shank or helical threaded shank nails. Such nails provide higher withdrawal resistance than plain shank nails of the same size. Other forms of improved nails are obtained by grooving or twisting of square cross-sectioned nails. The process of twisting not only modifies the nail surface but also work-hardens the steel, increasing its yield strength. Alternative types of nails are shown in Figure 10.1.

10.1.1.2 Screws

Wood screws are used in place of nails in applications requiring higher capacities, in particular in situations where a greater withdrawal capacity is required. They can be used for timber-to-timber joints but are especially suitable for steel-to-timber and panel-to-timber joints.

Screws should always be fixed by being threaded into the timber, not by being hammered into position and the characteristic strengths given for screws in EC5 [2] are based on this assumption. Where screws are used in softwood connections and the smooth shank diameter of the screw is 6 mm or less, pre-drilling is not required. Where the diameter is greater than 6 mm in softwood connections and for screws of any diameter in hardwood connections, pre-drilling must be used and the following requirements stated in 10.4.5 of EC5 will apply:

• The pre-drilled hole for the shank should have a diameter equal to the shank diameter and be of the same depth as the shank length.

• The pre-drilled hole for the threaded portion of the screw should have a diameter of approximately 70% of the shank diameter.

The most common types of wood screws are the countersunk head, round head and coach screw, which are illustrated in Figure 10.2.

Shank diameter, d

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