As a Builder, be aware that it is usually unnecessary to call out in working drawings the types of fasteners used for light frame construction. However, this is not the case, for heavy timber construction. To prepare drawings or estimate materials for timber structures, you need a working knowledge of timber fasteners and connectors and the manner in which they are used. The following text covers the more common types.
Bolts used to fasten heavy timbers usually come in 1/2-, 3/4-, and 1-inch diameters and have square heads and nuts. In use, the bolts are fitted with round steel washers under both the bolt head and the nut. The bolts are then tightened until the washers bite well into the wood to compensate for future shrinkage. Bolts should be spaced a minimum of 9 inches on center and should be no closer than 2 1/2 inches to the edge or 7 inches to the end of the timber.
Driftbolts, also called driftpins, are used primarily to prevent timbers from moving laterally in relation to each other, rather than to resist pulling apart. They are used more in dock and trestle work than in trusses and building frames. A drifibolt is a long threadless rod that is driven through a hole bored through the member and into the abutting member. The hole is bored slightly smaller than the bolt diameter and about 3 inches shorter than the bolt length. Driftbolts are from 1/2 to 1 inch in diameter and 18 to 26 inches long.
Butt joints are customarily connected using driftbolts; however, another method of making butt-joint connections is to use a scab. A scab is a short length of timber that is spiked or bolted to the adjoining members, as shown in figure 8-42.
A timber connector is any device used to increase the strength and rigidity of bolted lap joints between heavy timbers. For example, the split ring (fig. 8-43) is embedded in a circular groove. These grooves are cut with a special bit in the faces of the timbers that are to be joined. Split rings come in diameters of 2 1/2 and 4 inches. The 2 1/2-inch ring requires a 1/2-inch bolt, and the 4-inch ring uses a 3/4-inch bolt.
Shear plates are shown in figure 8-44. These connectors are intended for wood-to-steel connections, as shown in view(B). But, when used in pairs, they may be used for wood-to-wood connections as shown in view (C). When making a wood-to-wood connection,
Figure 8-42. - Scabs.
the fabricator first cuts a depression into the face of each of the wood members. These depressions are cut to the same depth as the shear plates. Then a shear plate is set into each of the depressions so that the back face of the shear plate is flush with the face of the wood members. Finally, the wood members are slid into place and bolted together. Because the faces are flush, the members easily slide into position, which reduces the labor necessary to make the connection. Shear plates are available in 2 5/8- and 4-inch diameters.
For special applications, toothed rings and spike grids are sometimes used. The toothed ring connector (fig. 8-45) functions in much the same manner as the split ring but can be embedded without the necessity of cutting grooves in the members. The toothed ring is embedded by the pressure provided from tightening a
Figure 8-43. - Split ring and split-ring joints.Continue Reading