Joist and Purlin Hangers
Framing connectors are manufactured to connect joists and purlins to supporting wood members. They are generally available for member sizes from 38 x 89mm (2" x 4") joists to 89 x 377mm (4" x 14") purlins or double joists.
Joists and purlin hangers are made from light gauge galvanized sheet metal and are affixed to wood members with special nails. As with framing anchors, the required number of nails must be used to provide the load-carrying capacity.
Hangers can reduce the overall depth of a floor or roof assembly or increase clearance below the framing where joists abut headers rather than rest on top of them as in Figure 5.7 below.
Truss plates are light gauge metal plates used to connect prefabricated light frame wood trusses. Truss plates are produced by punching light gauge galvanised steel (usually 16, 18, or 20 gauge) so that the teeth protrude from one side.
Since most truss plate designs are proprietary, north American engineering design standards do not provide design values but rather require that plates be tested and accredited to establish design values. There are a number of truss plate manufacturers and each has its own tooth pattern for which design values have been determined through testing and accreditation by independant testing agencies.
Light frame trusses connected with truss plates should not be used in corrosive conditions, or when fire-retardant treated lumber in wet service conditions due to the potential for loss of strengthif deterioration of the teeth takes place.
Truss plates are installed by first orienting the members to be connected and then pressing the plate into the members using a hydrolic press, roller, or ram.
Good practice dictates that: identical truss plates placed on opposite faces are directly opposite each other; the plates are not deformed during installation; the teeth are normal to the surface of the lumber; the teeth are fully imbeded in the wood so that the plate is tight to the wood surface ( the plate must not be imbedded into the lumber deeper than half the plate thickness); and the lumber where the plates are situated must not contain wane, loose knots, or knot holes.
Some other types of light metal connectors are shown in Figure 5.8 below, and many other types can be specially ordered to suit a specific need.
Figure 5.8: Miscellaneous Connectors