Pith-to-bark increment cores were obtained at breast height from 199 interior Douglas-fir parent trees located in the east Kootenay region of British Columbia. The cores were divided into equal lengths and were analyzed separately for wood density. The half portion close to the pith (inner half) was used to estimate the juvenile wood density; the outer half was used to estimate the wood density of the mature volume of the tree. The outer half was significantly higher in wood density than the inner half. When compared to other parent trees of the same species located in other interior seed zones, the outer half of these east Kootenay trees had significantly lower wood density.
The objective of this study was to determine the representativeness of density determined from a small size near the failure location of a lumber test specimen for the density of the total lumber specimen. Other objectives were: to check on the moisture distribution within parcels after the lumber had been stored in the laboratory for several weeks; and, to check on differences in density between species. Results, discussion, conclusions and recommendations are presented.
This report presents the results of a pilot study of the equilibrium moisture content and tensile strength of 20.5 mm thick Canadian Softwood Plywood and 15.9 mm thick waferboard exposed to a range of climatic conditions. Plywood and waferboard were conditioned until they reached constant weight at 20 C/65%RH and 5 C/90%RH. In addition some of the plywood and waferboard test specimens conditioned at high humidity subsequently were moved to a 20 C/65%RH atmosphere where they remained until an equilibrium moisture content had been achieved. A fourth group of plywood and waferboard specimens were kept at ambient conditions in the laboratory. Additional groups of plywood specimens were conditioned at 20 C/50%RH, 20 C/80%RH and also reconditioned from wet to 20 C/50%RH. Density, moisture content and tensile strength of all specimens were determined after they had reached equilibrium moisture content. The results indicate that there can be large differences in the equilibrium moisture content of wood-based panel products. The results also indicate a strong moisture dependency for the tensile strength of waferboard. No clear trend for the tensile strength of plywood in relation to moisture content could be established by this study.
The objectives of this project are to rationalize the compression perpendicular-to-grain design for lumber, glued-laminated timber and dowel connections in CAN3-O86 and propose characteristic strength values. Work concentrated on two areas: a finite element analysis of common wood to steel and wood to wood support bearing conditions incorporating nonlinear material behaviour; and, a comparison of the bearing values for lumber, glued-laminated timber and panel materials in CSA O86.1-1989.
To assure the appropriate use of wood in large residential and non-residential buildings, it is necessary to carry out a comprehensive study of the resistance provided by these wood structures to lateral loads due to wind and earthquakes. Given that this is a topic of international interest, and there is a strong movement towards worldwide harmonisation of codes and standards, the proposed work requires the cooperation of a number of specialists in Canada and abroad. As a first step in creating a coordinated program of research, a consultation on the seismic resistance of timber structures has been carried out. A group of six seismic experts from Japan, New Zealand, USA, Germany, Italy and Greece were brought together in Vancouver, B.C. for two days in May, 1993. This consultation was joined by six Canadian experts on seismic analysis and timber engineering research. Following this meeting, a five-year research program on the lateral resistance of engineered wood structures to seismic and wind loads was launched. The objective of the program is to provide designers and code writers with the test data and analytical tools needed to design large timber buildings for wind and earthquake forces. The program includes wood-framed and sheathed walls and diaphragms, braced timber structures, structural wood frames and arches. In the first year of the program, in cooperation with Dr. M. Yasumura, a visiting scientist from the Building Research Institute, Tsukuba, Japan, and Mr. D. Kishi, a structural engineering consultant from British Columbia, a total of 21 16' x 8' (4.8 m by 2.4 m) wood shear walls have been tested at Forintek under static and reversed cyclic loading. In these walls, three types of sheathing material (plywood, Oriented Strand Board, and Gypsum Wall Board (GWB) were used to investigate the effects of sheathing position (vertical or horizontal), blocking, nail spacing, and taping (in the case of GWB). The structural behaviour of elements such as shear walls is dependent on the behaviour of individual connections. Research alliances are currently being formed with the University of New Brunswick and the University of British Columbia for the development of test data and analytical models on the behaviour of connections.
The progress in the second year of the 5 year research program entitled "Lateral Resistance of Engineered Wood Structures to Seismic Loads" is presented. Because of the international scope of the problem, the work is being carried out in cooperation with scientists from several universities and research institutes. A procedure for determining force modification factors for timber structures is presented using the experimental data collected on nailed shear walls.
A literature survey on experimental data and analytical studies of the structural behaviour of wood framed shear walls and diaphragms has been carried out. The utility of various analytical methods for the study of internal forces in these structural elements due to external static or dynamic forces has been noted. It also has been concluded that the complexity of these analytical methods precludes their use as a tool for standard designs on a daily basis. For these standard designs currently established design methods will likely be continued to be used for some time. Establishment of design data by means of testing for panel thicknesses currently not included in the Canadian design code is recommended.
Tests were carried out to determine the resistance of lumber bolted to concrete and subjected to ramp loading in the longitudinal direction of the wood. Specimens were made from Hem-Fir and from SPF lumber. Anchor bolt sizes studied were nominal 1/2 in. and 3/4 in. in diameter. Both lumber and anchor bolts were representative of material usually used in the construction of low-rise timber structures. It was found that the minimum strength of a connection with a single bolt exceeds the characteristic strength used by current design procedures in CSA O86.1 by a factor of 1.6 for 1/2 in. diameter bolts and a factor of 2.0 for 3/4 in. diameter bolts. Reasons for this underestimate of the strength of bolted wood-to-concrete connections are attributed to (a) a low estimate of the calculated embedment strength of bolts in wood, (b) a low estimate of the embedment strength of bolts in concrete, (c) bolt yield strength 14 to 37 percent higher than that specified in CSA O86.1, and (d) lack of a model for the strength of bolted connections which accounts for the anchorage of wood provided by washers, and friction between the concrete and the wood member. Some changes in the current design method which would improve the ability of this procedure to predict the strength of bolted wood-to-concrete connections are recommended.