The National Design Specification for Wood Construction, American Forest & Paper Association, contains design provisions and design values for bolts with diameters up to 1 in conforming to the ANSI/ASME Standard B18.2.1. Bolt design values in the NDS apply to connections that have been snugly tightened and to connections that have loosened due to shrinkage of the wood components.
Following are some important NDS requirements for bolts: Bolt holes should have a diameter from 1â„32 to 1â„16 in larger than the bolt diameter. In establishment of design values, careful centering of holes in main members is assumed. Tight fit of bolts in the holes, requiring forced insertion, is not recommended. A metal plate, strap, or washer (not smaller than a standard cut washer) should be placed between the wood and bolt head and between the wood and the nut. The length of bolt threads subject to bearing on the wood should be kept to a practical minimum.
Two or more bolts placed in a line parallel to the direction of the load constitute a row. End distance is the minimum distance from the end of a member to the center of the bolt hole that is nearest to the end. Edge distance is the minimum distance from the edge of a member to the center of the nearest bolt hole. Figure 10.12 illustrates these distances, the spacing between rows, and the spacing of bolts in a row. NDS requirements are listed for minimum end distance in Table 10.34, for minimum edge distance in Table 10.35, and for minimum spacing between rows and between bolts in a row in Table 10.36. The geometry factor C discussed in Art. 10.14.5 is applied to the design value for a bolted connection when the end distance or spacing between bolts is less than that given in these tables for full design value.
