M.Ing. / Timber is an organic, orthotropic material of which the strength is currently not fully utilised in structural designs. Most design codes treat timber as an isotropic material with special clauses to compensate for the weaker strength across the grain. Several safety factors are used to accommodate the large variations in the strength of timber. In the orthotropic approach presented here, the unidirectional properties of timber are assumed as constant. It is also assumed that the large strength variation which is observed between samples of the same group, can mostly be attributed to the grain slope variation in a sample. The finite element method is employed to model grain slopes around a predetermined defect in a sample. The sample is then forced to fail at this defect, and the finite element model is then analyzed at the failure load to determine which stress combination led to the failure. Initial unidirectional material strengths are used in a failure criterion to evaluate the critical stress combination. The method of least squares is used to fit the predicted strength against the experimental strength. In this process new values are found for the unidirectional material strengths. The process is then repeated to determine whether another stress combination is not more critical than the original choice. As soon as the numerically acquired material strengths stabilise, it is compared with known values. The results indicate that the strength of a timber section can be predicted on the grounds of the observed fibre directions if the unidirectional material strengths are known.

Creep and recovery tests in compression parallel to the grain were conducted on 2 in. by 2 in. Douglas-fir specimens 4 in. long at four different levels of moisture. Specimens were loaded in stages up to a predetermined load. Instantaneous axial and lateral deformation as well as creep measurements were taken at each stage. Creep was observed over periods ranging from five minutes to twenty-five hours. Similarly, recovery was observed during unloading at successively lower stress levels. There are indications that creep as well as negative creep and negative recovery were mainly due to moisture present in the cell walls. Creep, In general, appeared to be more marked in the green specimens than in the intermediate and air-dry conditions. The only oven-dry specimen showed less creep than the air-dry specimens. Results also show that the values of the coefficient of lateral deformation(formula omitted) (both radial and tangential), during the load rise were entirely different from those during the period of creep, indicating that the corresponding deformations were entirely different. The µ’s for the change In load were always higher than those for the periods of creep. All specimens tested showed a recovery of more than 50% of the longitudinal creep. This indicates that creep in wood is made up of two parts, recoverable and permanent creep. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Present methods of determining design values for compression perpendicular to grain involves the testing of specimens of one specific geometry. The geometry of this test is very different from the geometries of bearing conditions occurring in practice. It was hypothesized that this test does not represent actual bearing conditions in practice and the object of this thesis was to find a more representative method of designing for compression perpendicular to grain. This thesis found the behaviour of wood in compression perpendicular to grain loading is strongly dependent on geometry in both the linear and nonlinear ranges of applied loading. A finite element analytical model, verified by testing, was used for the analysis. The analysis found the deflection is strongly dependent on the modulus of elasticity perpendicular to grain and nearly independent of other material properties. Also the capacity was found to be dependent on a characteristic material term and only weakly dependent on other material properties. A design method, one which includes an estimate of the deflection of the bearing plate, was developed from the results of this research. This proposed design method is valid for the capacities of the different geometries of bearing conditions occurring in practice. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The results of two hundred and fifty-eight static bending tests on young Douglas fir were obtained from the Vancouver Laboratory of the Forest Products Laboratories of Canada. Twenty-two trees had been sampled; seven of approximately sixty years of age from Port Moody, eight of about seventy years of age from Coombs (on Vancouver Island), and seven of approximately ninety years of age from Stave Lake. Stand site quality in each locality was similar and above average for second-growth fir from the coastal region of British Columbia. The laboratory's results were separated into two classes. Ninety-seven tests represented wood formed within the first five inches of radial growth in the tree. The remaining one hundred and sixty-one tests typified the older wood lying between the inner zone and the bark. Analyses of variance revealed highly significant differences in properties between zones. Wood from the inner zone had a faster growth rate, lower density (though wider bands of summerwood) and less strength and less stiffness in bending than wood from the outer zone. The influence of ring width, summerwood width and specific gravity on the moduli of elasticity and rupture was assessed for each zone by regression analyses. Ring width and summerwood width accounted for a significant amount of variation in modulus of elasticity and modulus of rupture in the two zones. Their influence on both moduli, however, was completely due to their association with specific gravity. Specific gravity, alone, accounted for almost twice as much of the variation in elasticity and bending strength as did ring width and summerwood width combined. The presence of compression wood in a few specimens from the outer growth zone weakened the relationship between modulus of elasticity and specific gravity in this zone but had no effect on the modulus of rupture — specific gravity relationship. In consequence, the influence of growth zone on modulus of elasticity could not be determined. The difference in average values of specific gravity between zones did not fully explain the similar difference between zones for average modulus of rupture values; an indication that radial growth zone in the tree had some influence on the bending strength independent to that exerted by density. / Forestry, Faculty of / Graduate

A high extractive-content temperate conifer wood (Pinus elliottii) was examined as a pulpwood source by organosolv pulping. Particularly, the behavior of the resin- and fatty acids during the lignin solvolysis process was studied in detail. For this purpose the resin-and fatty acids were characterized in the wood, and after pulping trials in order to reveal their fate during pulping, using catalyzed 80% aqueous alcohol (methanol) as solvent. Wood extractives were removed by both methanolic cold maceration and Soxhlet extraction techniques. The resin-and fatty acid fractions thus collected were saponified and/or methylated and characterized by gas liquid chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). No significant differences were found in regard to extraction efficiencies between the two types of cold extractions. Furthermore, there was no significant difference between these two types of cold extractions in comparison with the procedure described by TAPPI standard T 204 os-76. Pulping experiments were performed at 205°C for periods of 5, 20, 40, and 60 min. Lignins, which precipitated on cooling of the black liquor (Lignin fraction I), were set aside for further extractions and chemical analyses. The molecular weight distribution of these lignins was determined by size exclusion chromatography on an HPLC and their quantity was determined either gravimetrically or volumetrically. Precipitated Lignin Fraction I, suspected of containing some adsorbed extractives and some fiber fragments, was transferred to a tared crucible. The lignin and extractives were sequentially dissolved by using tetrahydrofuran (THF), acetone and methanol. This solution was evaporated, the residue redissolved in methanol-water (80:20) and the solution liquid-liquid extracted with diethyl ether in a separatory funnel followed by methylation prior to GC and GC-MS analysis. Quantification of the resin- and fatty acids in the wood and those recovered after organosolv pulping was performed using an internal standard (methyl heptadecanoate) added prior to the extraction steps. The extractives dissolved in the black liquor were isolated by a ternary liquid-liquid extraction scheme using diethyl ether, methylated with fresh diazomethane, and the resin- and fatty acids methyl esters characterized by GC and GC-MS. The extractives present in the pulp were isolated (removed) by a Soxhlet extraction procedure with methanol and" the resin- and fatty acids fractions characterized as above. Resin- and fatty acids surviving the high-temperature pulping process, were found mainly in the black liquor. After the 60 min cook, the black liquor contained 78.1% and 71.6% of resin- and fatty acids, respectively, while the pulp retained 11.7% and 8.2%, respectively of the extractives originally present in wood. "Lignin fraction I" adsorbed 10.2% and 20.2% of the resin- and fatty acids, respectively. Contrarily, if all of the lignin is precipitated (Lignin fraction II). prior to liquid/liquid extraction of the black liquor with diethyl ether, 98% and 60.4% of the resin- and fatty acids co-precipitate with the lignin and 2.0% and 39.6%, respectively, remain dissolved in the aqueous filtrate. Industrial organosolv lignin isolated after solvent pulping of pine was thus shown to contain most (98%) of the resin acids and 39.6% of the fatty acids normally found in pines. Although not tested, it is supposed that lignins isolated by precipitation from the black liquor after organosolv pulping of other species cannot be considered as "pristine lignins" as described hitherto in the technical literature, since such lignins are heavily contaminated by the extractives of the wood species. In light of these findings all data on chemical and physical characterization of organosolv lignins and their reactivity will have to be reexamined and reassessed to remove the effect of the extractives as contaminants. / Forestry, Faculty of / Graduate

A new approach to the problem of failure prediction of wood components and structures is that of fracture mechanics. In order to implement this approach knowledge of flaw growth (or crack propagation) in wood subjected to various stress systems and environmental conditions is required. The extension of flaws is accompanied by the release of energy in the form of acoustic or stress wave emissions, which can be detected and have been found to be reliable indicators of crack growth. Using acoustic emissions as a measure, flaw growth was investigated in stressed bending specimens of three species. The test pieces contained a variety of knot configurations, seasoning checks and resin pockets. Three wood moisture contents were used; specimen size was 2-by-4-inch (nominal) cross section and 50-inch length. A detailed description of the system used for detecting, measuring and recording acoustic emissions is given. Emission activity was measured using an electronic counter. Simultaneous count, load and deflection measurements were recorded and count-deflection and load-deflection curves plotted. The association between acoustic emissions and crack growth is discussed. Four types of integrated count- deflection patterns were found, which generally exhibited two common features. Firstly, a rate change point, where the count rate increased rapidly, and secondly a count increase just prior to failure. The rate change point was approximately coincident with the proportional limit in the load-deflection curve, suggesting an association between elastic behaviour and microfailure development. Several qualitative relationships between the count and load curves are presented. A correlation between stable crack growth and the entire load-deflection curve is postulated. The presence of checks and resin pockets affected the microfailure pattern, shown by increased acoustical activity, without appreciably influencing modulus of rupture. Green specimens for the most part produced lower counts than drier ones. Also clear or essentially clear boards exhibited lower emission counts. Species differences were not apparent. The estimation of modulus of rupture employing parameters from the count-deflection curves is discussed and compared to that using modulus of elasticity. Precision of the prediction was not improved using count parameters. A method for determining the direction of crack propagation in a fractured bending member is described. / Forestry, Faculty of / Graduate

The stress distribution near the centerline apex of pitch-cambered glulam beams is analysed. The analysis is done with an orthotropic trapezoidal finite element utilizing the stiffness approach. The element is tested with various grid sizes against known solutions and shown to give an overall accuracy to within five percent. Radial tension stresses perpendicular to grain due to moment, were calculated for various geometries and plotted as a design aid. These stresses can be several times those found in a uniform curved beam. The effect of changing the elastic moduli of the whole beam or individual laminations was investigated and found to be unimportant. Radial stress due to shear forces was found to be unimportant. Radial stress for one typical geometry due to moisture change was investigated in detail. This showed that ten pounds per square inch tensile stress was generated for a one percent change in moisture content. Twenty two tests were performed on tension perpendicular to grain to indicate that the allowable stress would be near thirty five pounds per square inch. A numerical example and design recommendations are included. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Because of an interaction between the load history and the material's properties a reduction in the serviceability of safety of a structure may be seen as the result of a random process of damage accumulation with time. A damage model is proposed and verified to deal with this type of problem in general, and specifically with duration-of-load effects in timber structures. Through comparisons with and discussion of other damage accumulation models, the proposed model is found to be both suitable to represent experimental results and relatively easy to use. A reliability analysis for a single structural member with a service life of 30 years is studied for different snow loading conditions of three Canadian cities,using the damage model in combination with Rackwitz-Fissler's algorithm. A simplified analysis method is proposed and compared with a large-scale Monte-Carlo simulation. The results of the reliability analysis are found to be satisfactory. Finally, the implementation of the reliability analysis in a simple design guideline for load duration effects is discussed. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

No description available.

A new method is presented for rapid differentiation between coniferous woods commonly found in mixtures in major lumber producing regions of British Columbia. The species mixtures differentiated are the group known as "spruce/ pine/ fir" (SPF) containing white spruce (Picea glauca Voss), lodgepole pine (Pinus contorta Dougl.) and subalpine fir (Abies lasiocarpa Nutt.); the pair western larch (Larix occidentalis Nutt.) and Douglas-fir (Pseudotsuga menziesii Franco.); and the group of western hemlock (Tsuga heterophylla Sarg.), Sitka spruce (Picea sitchensis Carr.) and amabilis fir (Abies amabilis Dougl.). The method entailed measuring the reflectance infrared spectrum of a sample set of small wood pieces at a resolution of two wave numbers, determining which wavelengths were useful for differentiating species through a combination of correlation analyses and principal component analyses and using measurements at these wavelengths to develop species models using discriminant analysis. These models were then used to classify a larger set of samples measured under the same conditions. This approach was used to classify both green wood samples and the same samples after freeze-drying. For the SPF group the most effective overall classification model for the dry samples used 30 wavelengths and correctly classified 76% of samples, including 74% of heartwood samples and 89% of sapwood samples. For the green samples, the most effective sort used 10 wavelengths and correctly assigned species to 83% of green samples representing 84% of heartwood samples and 76% of sapwood samples. Classification was unsuccessful when the same classification parameters were applied to a matched set of extractive-free SPF samples, indicating that the sorting criteria are dependant upon the presence of extractive chemicals, both in heartwood and sapwood. The same classification parameters applied to a SPF mixture from eastern Canada (black spruce (Picea mariana B.S.P.), white spruce (Picea qlauca Voss.), jack pine (Pinus banksiana Lamb.), red pine (Pinus resinosa Ait.), white pine (Pinus strobus L.) and balsam fir (Abies balsamea Hill) were less successful than for the western SPF mixture. This suggests that each species may have unique sorting criteria based upon the somewhat different extractive chemical complex present in its wood. For the western larch/ Douglas-fir, the most effective overall classification model used 18 wavelengths and classified 98% of dry samples correctly for both heartwood and sapwood. For green samples, the best sort used 12 wavelengths and correctly assigned species to 91% of green samples, representing 90% of heartwood samples and 91% of sapwood samples. For the western hemlock/ Sitka spruce/ amabilis fir mixture, the most effective sort for the dry samples correctly classified 83% of the samples, 85% of heartwood samples and 56% of sapwood samples. Classification of the green samples proved difficult, with the best sort only 67% correct and using 15 wavelengths. However, if only western hemlock and Sitka spruce were sorted, the effectiveness rose to 82%. / Forestry, Faculty of / Graduate