These are metal devices used with bolts or lag screws for producing joints with fewer fasteners without reduction in strength. Several types of connectors are available.
Usually, they are either steel rings, called split rings, that are placed in grooves in adjoining members to prevent relative movement or metal plates, called shear plates, embedded in the faces of adjoining timbers. The bolts or lag screws are used with these connectors to prevent the timbers from separating. The load is transmitted across the joint through the connectors.
Split rings are used for joining wood to wood. They are placed in circular grooves cut by a hand tool in the contact surfaces. About half the depth of each ring is in each of the two members in contact. A bolt hole is drilled through the center of the core encircled by the groove. For economic reasons, split rings are seldom used now because of the accuracy required for properly fabricating the wood members and the relative difficulty of installation.
A single shear plate is used for wood-to-steel connections (Fig. 10.13a and b).
When used in pairs, split rings may be used for wood-to-wood connections (Fig. 10.13c). Set with one plate in each member at the contact surface, they enable the members to slide easily into position during fabrication of the joint, thus reducing the labor needed to make the connection. Shear plates are placed in precut daps and are completely embedded in the timber, flush with the surface. As with split rings, the role of the bolt or lag screw through each plate is to prevent the components of the joint from separating; loads are transmitted across the joint through the plates. They are manufactured in 25â„8- and 4-in diameter.
Shear plates are useful in demountable structures. They may be installed in the members immediately after fabrication and held in position by nails.
Toothed rings and spike grids sometimes are used for special applications; but shear plates and occasionally split rings are the prime connectors for joints in timber construction requiring transmission of very heavy loads.
The NDS contains tables that give design values for shear-plate connections.
The tabulated values apply to seasoned timbers used where they will remain dry.
See Table 10.29 for wet service factors.
Design values for split rings and shear plates for angles between 0 (parallel to grain) and 90 (perpendicular to grain) may be obtained from the Hankinson formula:
Design values are based on the assumption that the wood at the joint is clear and relatively free from checks, shakes, and splits. If knots are present in the longitudinal projection of the net section within a distance from the critical section of half the diameter of the connector, the area of the knot should be subtracted from the area of the critical section. It is assumed that slope of the grain at the joint does not exceed 1 in 10.
The stress, whether tension or compression, in the net area, the area remaining at the critical section after subtracting the projected area of the connectors and the bolt from the full cross-sectional area of the member, should not exceed the design value of clear wood in compression parallel to the grain.
Tables in the NDS list the least thickness of member that should be used with the various sizes of connectors. The design values listed for the greatest thickness of member with each type and size of connector unit are the maximums to be used for all thicker material. Design values for members with thicknesses between those listed may be obtained by interpolation.
The NDS also lists minimum end and edge distances and spacing for timber connectors (Table 10.37). Edge distance is the distance from the edge of a member to the center of the connector closest to that edge and measured perpendicular to the edge. End distance is measured parallel to the grain from the center of the connector to the square-cut end of the member. If the end of the member is not cut normal to the longitudinal axis, the end distance, measured parallel to that axis from any point on the center half of the connector diameter that is perpendicular to the axis, should not be less than the minimum end distance required for a squarecut member. Spacing of connectors is measured between their centers along a line between centers.
