Effect Of Gap Size On Performance Of Metal-plated Joints In Compression
Keywords:Truss plates, compression, joint gaps, serviceability
Metal-plate splice joints with gaps between butting pieces of 2 x 4 lumber were tested in compression to evaluate the effect of gap size on joint serviceability performance. The current design methodology for compression splice joints was also evaluated. Specimens representing floor and roof truss compression joints, with 16- and 20-gauge plates of staggered and aligned tooth configurations, were tested for each of two gap sizes.
Generally, 20-gauge and 16-gauge plates on joints with 1/8 in. nominal maximum gaps buckled under compression loads while 16-gauge plates on joints with nominal 1/16 in. maximum gaps did not buckle before the gap closed. Gap closure with the latter joints was due principally to slip between the teeth nearest the splice and the wood. Joints with 16-gauge plates generally outperformed those with 20-gauge plates, based on the serviceability performance indicators of the test compression splice joints. Furthermore, gap size had less of an influence on joints with 16-gauge plates than on joints with 20-gauge plates.
The current practice of sizing plates for compression splices to withstand one-half of the calculated chord force could not be physically confirmed using joint serviceability criteria. The test results indicated that basing allowable plate ratings on a surface-area basis derived from tension tests is misleading.
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