A study was conducted with the primary objective of gathering information for the development of a protocol for evaluating the surface quality of cross-laminated timber (CLT) products. The secondary objectives were to examine the effect of moisture content (MC) reduction on the development of surface checks and gaps, and find ways of minimizing the checking problems in CLT panels. The wood materials used for the CLT samples were rough-sawn Select grade Hem-Fir boards 25 x 152 mm (1 x 6 inches). Polyurethane was the adhesive used. The development of checks and gaps were evaluated after drying at two temperature levels at ambient relative humidity (RH).
The checks and gaps, as a result of drying to 6% to 10% MC from an initial MC of 13%, occurred randomly depending upon the characteristics of the wood and the manner in which the outer laminas were laid up in the panel. Suggestions are made for minimizing checking and gap problems in CLT panels. The checks and gaps close when the panels are exposed to higher humidity.
Guidelines were proposed for the development of a protocol for classifying CLT panels into appearance grades in terms of the severity of checks and gaps. The grades can be based on the estimated dimensions of the checks and gaps, their frequency, and the number of laminas in which they appear.
Work reported in this study was carried out with the key objective of evaluating fasteners holding capacity in commercial wood panels for the purpose of exploring potential markets or expanding existing ones for OSB and other panel products in the upholstered furniture industry.
In order to have a better understanding of the upholstery furniture industry, visits were made to major upholstered furniture manufacturers in the Montreal area in November and December of 2003. These visits provided the research group with a comprehensive knowledge on the various types of wood materials and processing technologies being used at these plants, including ways of connecting the various components of the frames. Interviews with the plants staff indicated that fasteners holding capacity in OSB and other panel products are some of the major issues that are currently limiting the increased use of wood-based panels in the upholstered furniture industry.
In order to better understand the relationship between the fasteners holding capacity and the density distribution in panels, a comprehensive testing program was established. A total of 20 panels of medium density fiberboard (MDF), 16-mm thick, particleboard (PB), 16 mm thick, and oriented strand board (OSB), 11 mm, 15 mm, and 18 mm thick, with 4 replications each, were scanned using a commercial X ray system to obtain in-plane (horizontal) density distribution of the full size panels. In addition, basic panel properties (i.e., bending strength (MOR) and stiffness (MOE), internal bond (IB) and density profile) were determined. Sampling of test specimens from mapped panels was carried out in such away to cover low and high horizontal density zones.
Fasteners holding capacity tests including; lateral resistance of screws, edge and face withdrawal and head pull-through resistance of screws and staples were carried out. Correlations between fasteners holding capacities and localized horizontal density distributions were established in order to investigate how density distribution within the plane of the panel could affect the fasteners holding capacity. Investigations on the fasteners holding capacity in panel specimens subjected to static and cyclic loadings were made as well for the purpose of examining the effect of repeated cycles of loading and unloading events (i.e., short-term fatigue).
Findings from this study indicated that poor fasteners holding capacity especially on the edge of the panel is one of the key panel attributes that is currently limiting the use of OSB and other wood panel products in the upholstered furniture. Fastener driven in low density points or zones may fail at much lower load level than that driven in high density points with failure initiating at those low density zones and progressing to other zones from there (i.e., loaded end or edge distance). For the type of cyclic loading regimes used in this study (90 cycles at different load levels), no significant differences were observed.
Recommendations are given on how to improve the panel attributes in order to increase the fasteners holding capacity and resolve some of the technical issues limiting the market access of wood panel products in the upholstered furniture industry.
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.
