Lateral Tests of Wood Roof Sections Sheathed with Decking

Several roof sections, 20 by 60 feet and sheathed with nominal 3-inch. laminated decking, have been tested with lateral loading as diaphragms in recent years. Objectives of the tests were to obtain data for use in design for wind and earthquake forces and to improve the strength and stiffness of decking-type construction. The two roof sections that were stiffest and strongest were constructed with nominal 6- by 10-inch laminated joists spaced 12 feet on centers and sheathed with decking placed at right angles to the joists. For one diaphragm, a continuous bead of an elastomeric adhesive was applied between rows of decking to increase stiffness and strength; the other roof section was overlaid with 3/8-inch plywood oriented at 45 degrees with the decking. Lateral loads were applied at fifth points of one 60-foot chord. Maximum deflection occurred at mid-length of the opposite 60-foot chord. At loads of 500, 1,000, and 1,500 pounds per lineal foot (plf) of diaphragm width (multiply by 40 for total load), the roof section with adhesive deflected 0.59, 1.71, and 3.74 inches, respectively. The diaphragm overlaid with plywood deflected 0.29, 0.67, and 1.43 inches. A similar diaphragm with no adhesive or overlaid plywood deflected 6.9 inches at a load of 450 plf, which was ultimate load. Ultimate load for the diaphragm with adhesive was 1,500 plf. The roof section overlaid with plywood was not tested to failure; it was sustaining load, but nearing failure at 1,650 plf.

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