Geir I. Vestøl

Variability of density and bending properties of Picea abies structural timber

Abstract Density, modulus of elasticity and bending strength were measured on 333 boards from 54 Picea abies trees, sampled from six sites in a small area in southern Norway. The variability of the properties was analysed in a linear mixed model with relative tree size and log type as fixed effects, and with site and tree as random variables. Relative tree size was the most important fixed effect, and both density, MOE and MOR all decreased with increasing relative tree size. Log type explained a smaller part of the variance, but it was important when predicting MOR from MOE since these had different longitudinal variations.

Liquid water absorption in uncoated Norway spruce (Picea abies) claddings as affected by origin and wood properties

Abstract Uncoated Norway spruce specimens from different spatial positions within stems from two origins with different growth conditions were exposed to liquid water over a prolonged time, and apparent diffusion coefficients and rates of void filling were calculated from sorption curves. Both apparent diffusion and rate of void filling were significantly affected by origin and by the difference between inner and outer boards. The differences between inner and outer boards were explained by heartwood proportion and density, but some effects of origin remained when these properties were accounted for. The apparent diffusion coefficient was reduced by increasing density, and increased by increasing heartwood proportion. Void filling rate was reduced by both increasing density and increasing heartwood proportion. Since the effect of heartwood proportion was more pronounced in the material from the highly productive area, it may have been confounded with properties of juvenile wood.

Pre-sorting of Norway spruce structural timber using acoustic measurements combined with site-, tree- and log characteristics

This study assesses whether acoustic velocity alone or in combination with information about the timber obtained in the forest or on the log-yard can be used for pre-sorting of Norway spruce (Picea abies [L.] Karst) structural timber. The study is based on 1235 boards from 205 trees sampled from 14 sites in Norway. In addition to various site-, tree- and log variables, acoustic velocity was obtained by Fibre-gen tools, the ST300 on standing trees and the HM200 on logs. Both ST300 and HM200 explained parts of the variability of the indicating property measured by Dynagrade strength grading machine, but the accuracy was better for HM200 than for ST300. The model with ST300 was substantially improved by introducing forest data, i.e., height to diameter ratio, age and relative longitudinal position in the tree while the improvement by combining HM200 with log data, i.e., log tapering, was minor. Grade yield after pre-sorting based on the developed models was simulated, and the results showed a possibility of increasing the C30 yield. The results show that acoustic velocity could be used either as an inventory tool, to give information about the available material from a site, or as a pre-sorting tool before sawing the logs to certain products.

Impact of various measures to optimize the air velocity in an industrial wood-drying process

Abstract The relationship between fan speed and electrical energy consumption, and the price of energy, justify studies on the possibilities for reducing air velocity during the wood-drying process. In this study, effects of air velocity were examined to determine when and how much it can be reduced, without affecting the drying rate of the sawn timber. The first experiments were performed in a laboratory kiln, and 36 samples of 50×100 mm boards (2×log) of Norway spruce [Picea abies (L.) Karst.] were dried at 70°C with varying air velocity. Results show that too early or too sharp a reduction in air velocity gives a reduced drying rate and a large variation in moisture content. The next step in the project was a full-scale industrial study in kilns at a Norwegian sawmill. To optimize air velocity conditions, batten spaces were sealed. This had no significant effect on air velocity in the kiln. A reduction in air velocity in the kiln to 60% frequency at 40% moisture content and to 40% frequency at 20% moisture content, without considerable changes in the drying schedule, resulted in an increase in final moisture content.

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

ABSTRACT 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.

Variation in treatability of Scots pine sapwood: a survey of 25 different northern European locations

The treatability of Scots pine sapwood sampled from 25 locations in northern Europe, which was impregnated with an experimental furfuryl alcohol mix, was studied. A large variation in treatability was found between stands. The treatability was affected by anatomical properties of the trees and therefore also by the immediate climate, the sociological position of the tree in the stand, growth increments and on-stand competition. With the models applied, most parts of the differences in treatability between stands could be explained, while the treatability variation between trees within a stand remained mostly unexplained. Wider annual rings and higher latewood contents were found to increase the treatability. Models that included data on growth conditions and climate explain more of the variation in treatability, indicating that also other anatomical properties are influencing the treatability. Tree attributes and growth conditions that reduce annual ring width and latewood content decreased the treatability. Trees growing under warmer conditions and developing larger growth increments were easier to impregnate. Wood from trees growing near the timberline and under environmental conditions impairing wood growth was more difficult to treat.

Modelling the effects of timber length, stand- and tree properties on grade yield of Picea abies timber

Abstract When the grade is determined by the worst part of a board, the grade yield will decrease with increasing timber length. This length effect varies due to longitudinal variation in the grading features and their appearance on the sawn surface. In this study models identifying the length effects dependence on site, stand, tree and log-level characteristics have been developed. The study comprised boards from 160 Norway spruce trees (Picea abies (L.) Karst.) sampled from six sites in Norway which were selected based on variation in the occurrence of ramicorn branches, forked trees and sinuosity of stems. The boards were visually graded according to appearance by Nordic Timber and strength was graded by INSTA 142. The negative effect of increasing length on grade yield was strongest at stump level and decreased upwards in the trees. The biggest trees within a stand were most affected by an increase in length. In addition to timber length, position of the board within the tree was the most important factor influencing grade yield. The variation in grade yield within stands was greater than between stands for this material. The models predicting grade probabilities seemed to fit within a 10% margin.

Effects of Outdoor Weathering and Wood Properties on Liquid Water Absorption in Uncoated Norway Spruce Cladding

A comparison of liquid water absorption in uncoated Norway spruce (Picea abies L.) claddings before and after 1 year of outdoor weathering was performed. The study was based on 150 specimens from t...

Bending strength and modulus of elasticity of Pinus sylvestris round timber from southern Norway.

Abstract To enable use of round Scots pine timber in structural frameworks it is necessary to estimate the mechanical properties of the material. This paper presents data on density, bending strength and modulus of elasticity (MOE) of 533 debarked Scots pine logs with diameter from 75 mm to 250 mm sampled from 10 sites in southern Norway. The results show that round timber can have high values of bending strength and MOE, depending on the sites from which the trees have been collected. Some of the variation in bending properties can be explained by visual characteristics, but since a significant proportion of the residual variance is related to sites, criteria for visual strength grading have to be conservative to be valid across all sites. The potential for machine grading based on measuring MOE is better since this model is more accurate and the random effect of site is smaller.

Bending strength and modulus of elasticity of squares with wane as compared with round timber of Scots pine (Pinus sylvestris).

A comparison of bending strength and modulus of elasticity (MOE) of squares with wanes to round timber was performed as part of a project on the use of round Scots pine (Pinus sylvestris L.) timber...