Variation of tensile strength along the length of lumber

Summary A model has been developed for the within member variation of tensile strengths parallel to grain in nominal 38 × 89 mm No. 2 Spruce-Pine-Fir lumber. Tensile strength data from two modulus of elasticity matched groups were considered. Model parameters obtained from data group 1 were used to generate tensile strength profiles of lumber 6.10 m long. Within member tensile strength cumulative probability distributions of the simulated data were evaluated by window analyses. The spatial correlation of the simulated data were evaluated by semivariogram and regression analyses. Good agreement was obtained between model predictions and test results of both groups.The authors gratefully acknowledge the support of the Canadian Forest Service and the technical assistance of Mr. H. Sue, Mr. B. Deacon and Dr. J. Cook for this study. The research was performed while the principal author was working at Forintek Canada Corp.     

The critical stress in various stress levels of bending member on fire exposure for mechanical graded lumber

This study focused on the relationship between stress level and the fire resistance of structural lumber. The 210 samples were prepared from 15-year-old trees of Acacia mangium from the Forest Estate Plantation, Indonesia. Specimens were 20 ® × 20 (T) × 500mm (L) and were air-dried. Sixty samples were tested under four-point bending stress to obtain the modulus of elasticity (MOE) and the modulus of rupture (MOR) for classifying the stress grades of the remaining 150 samples. The tests were performed using a four-point load bending position at various stress level while the specimens were exposed to fire along the shear-free region. Time to failure was affected by the stress levels in an exponential trend. Despite changes in stress level, charring rate, and time to failure, the critical stress of a member from the same species was similar. The fire performance under applied load could be predicted by using simplified fire-testing methods. The developed testing apparatus is valid for evaluating the small-scale fire resistant behavior of structural lumber in bending.     

The temperature and moisture content in lumber during preheating and drying

Summary The time required to thoroughly preheat/presteam green 8/4 (51 mm) thick red pine and white birch lumber was determined. Thermocouples imbedded in the centre of samples were used to determine presteaming/preheating times for experimental material. These data were then compared to time determined by analytical methods (using formulae developed by Kollmann). No significant differences were found.During the subsequent drying period data were collected on interior wood temperature, mousture content and gradient. Results of the drying tests indicated: i) interior temperature increases in direct relation to elapsed time, ii) moisture content drops exponentially with elapsed time, and iii) an exponential relationship exists between average moisture content and the core temperature of the lumber.Results indicate that monitoring of the lumber drying process through measurements of interior wood temperature may be feasible.The first author was visiting Canada under the Chinese Scholar Program established by the Council of Ministers of Education, Canada. His research work was carried out at Forintek Canada Corp., Eastern Laboratory, OttawaThe authors would like to acknowledge the assistance and support of the following: Dr. M. Y. Cech, Manager, Lumber Manufacturing Technology, Forintek Canada Corp., Eastern Forest Products Laboratory-Senior Project Supervisor, and Mr. F. Pfaff, Research Scientist, Forintek Canada Corp     

Potential of Phytophthora pinifolia to spread via sawn green lumber: a preliminary investigation

Phytophthora pinifolia causes the needle and shoot disease of Pinus radiata in Chile known as Daño Foliar del Pino. Although P. pinifolia is primarily a needle pathogen, there are concerns that it might be spread to new environments via the export of contaminated timber. In order to determine whether P. pinifolia can enter or persist in green sawn lumber, its presence in lumber produced from trees exposed to the pathogen for at least four years was examined. Green lumber produced from the infected trees, and green wood samples artificially exposed to P. pinifolia inoculum, were analysed by making extensive isolations on Phytophthora selective media. In addition, PCR was conducted using species-specific primers developed for P. pinifolia. Results of the study showed that the green sawn lumber taken from trees infected by P. pinifolia, or green lumber exposed in infected pine plantations, displayed no evidence of the pathogen surviving in this material.     

Feasibility of near-infrared spectroscopy for online multiple trait assessment of sawn lumber

Near-infrared (NIR) spectroscopy coupled with multivariate analysis was applied to estimate multiple traits of sawn lumber. The effects of the lumber conveying speed (LCS) and measurement resolution of spectra (MRS) on the calibrations were examined. NIR spectra ranging from 1300 to 2300 nm were acquired at LCSs of 10, 20, and 30 m/min and at MRSs of 2, 4, and 16 nm. Prediction models of bending strength (F _b), modulus of elasticity in bending tests (E _b), dynamic modulus of elasticity (E _fr), and wood density (DEN) were developed using partial least-squares (PLS) analysis. LCS and MRS did not significantly influence the calibration performance for any wood property. The regression coefficients also showed no clear differences for any of the conditions. This indicates that the important explanatory variables included in the models are not greatly influenced by these measurement conditions. PLS2 analysis results, when presented graphically, allowed easy interpretation of the relationships between wood mechanical properties and chemical components, e.g., bending strength and stiffness were mainly related to polysaccharides cellulose and hemicellulose. NIR spectroscopy has considerable potential for online grading of sawn lumber, despite the harsh measurement conditions.     

Variation of tensile strength along the length of lumber

Summary The within member variation of tensile strength parallel to grain in nominal 38×89 mm No. 2 Spruce-Pine-Fir lumber has been experimentally evaluated. Window analyses yielded the within member tensile strength cumulative probability distributions of lumber segments with various lengths. Semivariogram and regression analyses have been performed to characterize the spatial correlation of the tensile strength of lumber. The results indicate that the tensile strength values within a piece of lumber separated by a distance greater than 1.83 m can be considered statistically independent.The Authors gratefully acknowledge the support of the Forestry Canada and the technical assistance of Mr. H. Sue, Mr. B. Deacon and Dr. J. Cook for this study. The research was performed while the principal author was working at Forintek Canada Corp.     

Impact of precommercial thinning on tree growth,lumber recovery and lumber quality in Abies balsamea

Abstract

Precommercial thinning (PCT) is often used to improve stand growth and value. While PCT may accelerate tree growth and reduce mortality, it may also have a negative effect on product quality. This study examined the effect of moderate and heavy thinning on tree growth, lumber recovery and quality in a natural balsam fir [Abies balsamea (L.) Mill.] PCT trial 35 years after thinning. Compared with the control, the heavy thinning increased merchantable tree diameter, stem volume per tree and lumber volume recovery per tree by 41.1%, 100.9% and 92.7%, respectively, reduced the Select Structural grade (the best grade) recovery by 33.7%. Thinning did not affect the no. 2 and better grade yield. There was a 12.2% and 15.0% difference, respectively, in the lumber bending modulus of elasticity (MOE) and modulus of rupture (MOR) between the control and heavy thinning. Moderate thinning had little impact on the visual grade recovery, lumber bending MOE and MOR. Heavy thinning is recommended if the goal is to get sizeable sawlogs in the shortest time, whereas moderate thinning is preferable if the intention is to minimize the negative effects on lumber quality while retaining modest tree growth and lumber recovery. Overall, PCT of very dense young balsam fir stands appears to be an effective and viable silvicultural treatment.     

Increased planting density as a means for improving Pinus elliottii lumber stiffness

Faster growth and reduced harvesting ages are causing a reduction in the stiffness of lumber from South African grown pine plantations. The objective of this study was to determine whether increased planting densities of Pinus elliottii would result in improved stiffness of its sawn lumber and whether it would affect other relevant lumber properties. Four planting density treatments (403, 1 097, 1 808, and 2 981 stems ha^?1) of a 12-year-old experimental spacing trial were processed into lumber. The static modulus of elasticity (MOE_stat), modulus of rupture (MOR), warp, knot properties and density of the lumber were measured for 172 boards. Results showed that the planting density had a significant effect on the MOE_stat of the lumber. The higher mean MOE_stat (up to 27% increases) of lumber from densely planted trees seems to be the result of the higher slenderness and the slower diameter growth of these trees. Planting density also had a significant effect on the twist, knot area ratio and the number of knots per board. The magnitude of the effect on each of these properties, however, was relatively low.     

Acoustic and bending properties in Pinus elliottii beams obtained from trees of different ages

In contrast to wood from native forests, the lumber harvested from planted forests is primarily composed of boards from younger trees. Given the possibility of using wave propagation methods to classify wood for structural purposes, it is important to evaluate if the ultrasonic parameters tend to vary with the age of the tree in a similar manner as static bending parameters. Experiments were conducted using structural beams taken from Pinus elliottii trees that were 8, 9, 13, 15, 22 and 23 years old. The beams were tested by ultrasound in the longitudinal direction and by static bending. The results showed that age of the tree influences the wave propagation velocity, stiffness constant and modulus of elasticity. The results were sorted into two groups based on the variation of these parameters: wood pieces from trees up to 15 years old and wood pieces from trees older than 15 years of age. Statistically, the flexural strength did not change with age due to the significant influence of knots on this parameter, which overcomes the influence of age. The data obtained by ultrasound follow the same trends with age as the elastic modulus in static bending.     

Between- and within-site variation of density and bending properties of Picea abies structural timber from Norway

This study provides an analysis on the variability of structural timber of Norway spruce (Picea abies) grown in Norway. Density, modulus of elasticity (MOE) and bending strength were measured on 1188 boards from 205 trees, sampled from 14 sites throughout Southern Norway, Eastern Norway and Trøndelag. The area represents the procurement area for the majority of Norwegian sawmills. The variability of the timber properties was analysed in a linear mixed model where the random variance was divided into variance due to site, variance due to trees and within-tree variance. Models describing variance due to site based on site index, altitude and latitude were developed, and combined with data from the Norwegian National Forest Inventory to estimate mean values and variability of the timber properties. The results showed that major parts of the variance due to site are explained by altitude and site index, and for density also by latitude. Major parts of the variance due to site and the variance due to trees in bending strength and MOE were explained by density.     

Outdoor exposure tests of structural laminated veneer lumber (II): evaluation of the strength properties after nine years

To investigate the durability of structural laminated veneer lumber (LVL), outdoor exposure tests have been conducted since 1990 at a field-testing site at the Forestry and Forest Products Research Institute. This article is the second interim report on the results after 9 years of exposure. Seven kinds of structural LVL with no preservative treatment were subjected to the tests. Almost all the exposed specimens were decayed by a kind of brown rot fungi (Pseudomerulius aureus (Fr.) Julich). The degree of decay varied with wood species; grand fir and western hemlock LVL in particular showed weak resistance against the decay. All the specimens were stored for more than 1 year in a testing room conditioned at 20°C and 65% relative humidity. We then measured the ultrasonic velocity of the specimens by the Pundit method, penetration depth by the Pilodyn method, and bending strength by a conventional bending test. Correlation between nondestructive measurement factors and the density was strong even on LVL with many adhesive layers. The nondestructive testing method was found to be applicable to LVL as well as solid lumber. After the nondestructive measurements, each LVL was cut into three types of specimen (top: T, middle: M, and bottom: B) for the bending tests. The bending strength varied with the type of specimens. Correlation between modulus of elasticity and modulus of rupture was strong even in the decayed specimens.     

Dynamic modulus of elasticity and bending properties of young Taiwania trees grown with different thinning and pruning treatments

The effects of different thinning and pruning methods on the bending strength and dynamic modulus of elasticity (DMOE) of young Taiwania (Taiwania cryptomerioides Hay) were investigated. The average DMOE, modulus of elasticity (MOE), and modulus of rupture (MOR) in the thinning treatments showed the following trend: no thinning > medium thinning > heavy thinning. This indicates that thinning reduces average bending properties. The average DMOE, MOE, and MOR in the pruning treatments showed the following trend: medium pruning > no pruning > heavy pruning. According to this tendency, better average qualities of lumber and specimens were from wood subjected to no-thinning and medium-pruning treatments according to an ultrasonic wave technique and static bending tests. However, most results showed no statistically significant differences among thinning, pruning, and thinning and pruning treatments. The average values of DMOE, MOE, and MOR of visually graded construction-grade lumber were significantly greater than those of below-grade lumber. Moreover, there were very significant positive relationships between density, ultrasonic velocity, DMOE, MOE, and MOR, although the determination coefficients were small.     

Heartwood development and its relationship to growth in Pinus radiata

Summary The rate of heartwood development was examined at four heights in stems of Pinus radiata D. Don from 18 mature stands in south-eastern Australia. While the diameter of heartwood tended to be greatest at stump and breast heights, formation commenced earlier (i.e. with fewer sapwood rings) and/or progressed more rapidly 10–20 m above ground level. Appreciable variation in heartwood development was detected between trees in the same and different stands, with both environmental and genetic factors apparently important. Regression analyses involving three parameters of heartwood development (number of rings, diameter and percentage area) and stem characteristics including height, diameter and ring width suggested that heartwood formation is affected little by tree vigour in the post-juvenile growth phase. Rather it seems that the rate at which annual increments are included in heartwood is largely fixed for any particular height level and stem. Thus the amount (but not necessarily the percentage) or heartwood in a stem is substantially dependent on diameter growth early in tree life.The expert technical assistance of Mr. R. Colley is gratefully acknowledged. Valuable assistance in the measurement of heartwood dimensions was also provided by Ms. V. Kurz and Mr. C. Slatyer. Dr. R. K. Bamber and Mr. A. P. Wilkins offered particularly helpful advice     

Effect of speed on the accuracy of stress-grading machines for lumber

Summary A computer simulation model is developed for predicting modulus of elasticity (E) of uniform lumber measured at high speed by stress-grading machines of the constant-deflection type. Simulations carried out with the model showed that speed had no significant effect on the average E measured along the lumber but largely affected E values measured at individual locations. Tests conducted at 15, 150 and 315 m/min with two machines employing different supports conditions confirmed model predictions. Ability of the grading machines to identify local E values at high speed could be improved by proper filtering of the load signal recorded by the machine.Experimental data analysed in this paper were collected when the author was a Research Scientist at Forintek Canada Corp., 6620 N.W. Marine Dr., Vancouver, B.C., Canada, V6T 1X2. The author is grateful to H. Fraser and L. S. Olson from Forintek for their assistance in perfoming the experiments. Financial support of the Natural Sciences and Engineering Research Council of Canada is gratefully achnowledged.     

Lignin distribution in wood from a progeny trial of genetically selected Pinus radiata D. Don

Summary Cell wall lignin distribution was assessed in Pinus radiata wood using quantitative interference microscopy. Three groups of trees were examined. Five trees, offspring of NZ clone 850-55, and five trees of NZ 850-55 crossed with several parents of the Guadelupe provenance, were compared with five trees of unselected P. radiata. Lignin concentration in the cell corner middle lamella region was significantly lower in both offspring groups of NZ 850-55 when compared with the unselected control trees. No difference in S2 lignin concentration was observed among the three groups. This result represents the first indication that variations in lignin distribution are genetically controlled in pines.The author gratefully acknowledges the assistance of Dr. C. J. A. Shelbourne, Mr. G. D. Young, FRI, and Mr. R. S. Foster, Papro (NZ), during the course of this work     

Variation in wood properties of Pinus kesiya Royle ex Gordon (syn. P. khasya Royle; P. insularis Endlicher); Eighteen trees of Burma provenance grown in Zambia

Summary The variation of six wood properties was studied within and between eighteen trees of Pinus kesiya Royle ex Gordon (syn. P. khasya Royle; P. insularis Endlicher) grown in Zambia from seed of Burma provenance and exhibiting 16 annual rings at 5 ft. above ground. Three trees represented each of two size classes in each of three thinning treatments. Thinning effects were poorly estimated but heavy thinning increased ring width, decreased latewood percentage and caused marginal decreases in tracheid length and density. The two tree classes differed in ring width characteristics. Individual trees varied particularly in density; significant height effects were detected for tracheid length and density. Latewood width (mean 0.9 mm) and grain angle (-1.2°) varied little but total ring width (5.8 mm), latewood percentage (19.6%), tracheid length (4.6 mm) and density (0.46 g/cm³) exhibited systematic patterns of variation within trees; quadratic polynomials including ring number and height as independent variables explained 80 to 90% of the variation. Radial differences were often statistically significant but practically unimportant. For plantation surveys many trees should be sampled by 3–4 annual rings on two radii at breast height.Wood samples were supplied by the Zambian Forest Research Division. Laboratory work was undertaken at the Tree Improvement Research Centre, Agricultural Research Council of Zambia, P. O. Box 1210, Kitwe, Zambia. The author acknowledges the laboratory assistance of Miss P. Waters, Mr. J. Mweetwa, Mr. F. Mulimbwa and Mr. N. Phiri. Data were processed on the IBM 360 computer of the Anglo-American Corporation, Kitwe, and on the KDF 9 computer of the Oxford University Comuting Laboratory; Mr. I. A. andrew, Mr. P. G. Adlard and Mrs. T. Posner assisted at various stages.     

Heartwood formation in living stumps of Douglas-fir

Summary An anatomical and chemical examination was made of living stumps of Douglas-fir. Changes in heartwood and extractives formation are not significant under the conditions of severe physiological stress that existed unless cell morphology was also altered. It is proposed that the factors controlling the amount and composition of heartwood extractives are incorporated in the ray cells during the early stages of their development.The authors are particularly grateful to Mr. J. Walters, Director of the Research Forest and to Professor J. A. F. Gardner, Dean of the Faculty of Forestry, of the University of British Columbia, Canada for their considerable help in the collection and transport of the samples of living stumps which formed the basis of this investigation. They are also grateful to Mr. A. Ceselli, Mrs. J. Juricskay and Miss D. Muston for assistance in the anatomical studies.     

Moisture and blue stain distribution in mountain pine beetle infested lodgepole pine trees and industrial implications

Healthy lodgepole pine trees and trees at three stages (green, red and grey) of infestation by mountain pine beetles (MPB) were examined for moisture and blue-stain distribution in the radial and longitudinal directions. The sapwood moisture content of trees dropped about 100% from the healthy stage while the heartwood moisture dropped about 10%, regardless of green, red or grey attack stages. Moisture content variation with tree height was unique up to the time since beetle attack. The volume of blue stain increased with increasing time since beetle attack. Maximum discolouration in wood occurred at about 3 m above ground level and expanded rapidly upward. Lumber sawn and tracked from the MPB attacked logs showed a decrease in moisture content with increasing time since beetle attack, indicating the need for specific drying schedules employing lower energy levels. The economic implication of the effect of blue stain was evaluated by the percentage of Japanese grade (J-grade) lumber produced. The J-grade lumber yield decreased with increasing time since beetle attack. Early harvest and conversion of MPB infected trees will positively impact product value and recovery. Part of this research was funded by Forestry Innovation Investment Ltd., Government of British Columbia.     

Moisture content adjustments for dynamic modulus of elasticity of wood members

The influence of moisture content (MC) on the dynamic modulus of elasticity of structural lumber was investigated using transverse vibration testing methods. The flexural rigidity (EI) of a transversely vibrating beam was calculated as the modulus of elasticity (E) multiplied by the moment of inertia (I). The increase in E of lumber due to reduction in moisture content was computed by assuming that the flexural rigidity remains constant with changes in moisture content. Reductions in I due to shrinkage were compensated by the increases in E which led to a proposal for a species-dependent MC adjustment model for modulus of elasticity. The model was validated using 38 mm × 89 mm × 4,290 mm western Canadian Spruce–Pine–Fir dimension lumber evaluated in the “as-received” and “dry” conditions. Results obtained from the species-dependent model agreed closely with those from the E adjustment equation for dimension lumber given in ASTM D 1990. The results show that the ASTM moisture adjustment procedures can be used to adjust dynamic E values for changes in moisture content also.     

Modulus of elasticity declines with decreasing planting density for loblolly pine (Pinus taeda) plantations

Context

Loblolly pine is often grown in intensively managed plantations for wood production. In order to fully evaluate the effects of management practices on wood quality and ultimately value, it is necessary to relate mechanical properties to management practices.

Aims

The aim of this study was to evaluate the effect of planting density on mechanical properties of lumber recovered from loblolly pine trees from a 27-year-old spacing trial and develop prediction equations for modulus of elasticity and modulus of rupture from stand, tree, and board characteristics.

Methods

Regression methods were applied to sample trees from three planting densities (2,989, 1,682, and 746 trees ha^?1) and used to relate mechanical properties of lumber extracted from the trees to stand, tree, and board characteristics.

Results

Initial planting density was found to be correlated with modulus of elasticity and, to a lesser extent, with modulus of rupture. Including board characteristics and utilizing the visual grade and board position as regressors produced improved prediction equations.

Conclusions

The mean modulus of elasticity declines with decreasing planting density while the variability increases, suggesting that planting density is a surrogate for frequency and size of knots. Thus, lower planting densities, while producing more lumber, may produce proportionally fewer boards of greater modulus of elasticity than higher planting densities.