A series of plywood and laminated veneer lumber (LVL) panels were prepared using incised veneers in the second phase of this two year project. The primary purpose of the work was to evaluate the effects of steam injection on the pressing times. A secondary objective was to expand the study of warpage in three-ply and four-ply plywood which was begun in phase one. Thirteen-ply 40 mm (1 5/8 inch) thick panels were evaluated for press times and thin 9.5 mm (3/8 inch) and 12.5 mm (1/2 inch) panels were evaluated for cupping and bowing. Press temperatures of 150 degrees C, 175 degrees C and 204 degrees C were used with a commercial adhesive mix for the LVL study while normal plywood pressing conditions were used for the plywood. For the plywood warpage study, the effect of lathe check orientation and species mix were evaluated. The lathe check orientation had little effect while the surface veneer species had a pronounced effect on the warpage in the plywood. Steam used for injection was heated to 260 degrees C at 450 KPa (65 psi) with a super-heater. All panels were made with incised 3.2 mm (1/8 inch) SPF veneers. The project demonstrated that steam injection can shorten press times by fifty percent if incised veneers are used.
At the request of the Council of Forest Industries, a simplified (hand-calculation) design method has been proposed for estimating the ultimate shear capacity and load-deflection response of wood-framed and panel-sheathed diaphragms, by Forintek's Wood Engineering Department. In its current form, the simplified code design approach can predict ultimate shear capacity for a wide range of (blocked) diaphragm constructions, sheathed with panels ranging from 7.5 mm (3/8") to 18.5 mm (3/4") in thickness, with a 22% coefficient of variation. This is comparable to the 21% variability exhibited by the current Canadian diaphragm design method, and not alarmingly larger than the 16% shown by the more detailed APA design method. Indeed, for the three high-shear diaphragms sheathed by 18.5 mm (3/8") Douglas-fir plywood panels, the proposed simplified design method yielded shear prediction errors of only 0%, 1% and 6%. Furthermore, simplified functions were also able to provide good estimates of diaphragms failure mechanisms, and their load-deflection patterns, as measured in earlier verification tests. Predictions from the simplified model need to be experimentally verified for high shear capacity diaphragms sheathed in thick panels fastened to glulam frames by large diameter nails; before its possible introduction to the Canadian wood design code.
