Performance of Trussed Rafters

Three types of metal plate fasteners and plywood gusset plates of common design were used in fabrication of trussed rafters. The trusses were of a W-type with a span of 26 feet and a slope of 3 in 12. Nearly defect-free western hemlock 2 by 4 lumber was used. In testing, the lower chords of the trusser were dead-weighted with buckets of sand to represent a load of 20 pounds per lineal foot of chord length. Variable loads were placed on the upper chord by means of calibrated hydraulic pistons. The metal plate with circular punched holes exhibited slightly greater resistance to creep deflection that did the other two metal plates. The best performance in all tests was given by the trussed rafters with nail glued gusset plates (frequently by a factor of two).

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