Bolts (Heavy Connections)
Bolts are used with plates, washers, or more efficiently, in conjunction with split rings or shear plates to connect wood members. They are often used in purlin to beam, beam to column, or column to base connections of wood structures. When bolts are used alone with washers or side plates as shown in Figure 5.9 below, the load transfer area of the wood is the surface area of the bolt.
Timber connectors such as split rings and shear plates are a means of distributing loads over a larger area of wood and are discussed later in this section.
Several types of bolts as shown in Figure 5.10 below, are used for wood construction with the hexagon head type being the most common. Countersunk heads are used where a flush surface is desired. Carriage bolts can be tightened by turning the nut without holding the bolt since the shoulders under the head grip the wood.
Depending on diameter, bolts are available in lengths from 75mm (3″) up to 400mm (16″) with other lengths available on special order. Where long length is required, threading rods may be used in lieu of bolts, either alone or with shear connectors.
Placement of bolts is important in design since it can affect load carrying capacity. Minimum end distance is based on bolt diameter and wood species, while minimum edge distance and spacing requirements are based on bolt diameters.
The net section of wood members (area of wood remaining after drilling of holes) in a bolted joint must also be checked by referring to wood engineering codes.
Figure 5.9 Loading Arrangements for Bolts