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.     

Dynamic modulus of elasticity and bending properties of large beams of Taiwan-grown Japanese cedar from different plantation spacing sites

The effect of plantation spacings (types A-E) on the bending strength and dynamic modulus of elasticity of 41-year-old Taiwan-grown cedar (Cryptomeria japonica D. Don) was investigated. The results indicate that the highest values for the static bending modulus of elasticity (MOE), modulus of rupture (MOR), and dynamic modulus of elasticity (E_D, E _Dt) occurred in trees obtained from those most densely planted (type A); there was a significant difference between type A and the other four spacing types (B, C, D, and E), but there were no significant differences among those four types. Interrelations among MOE, MOR, E _D, and E _Dt could be represented by positive linear regression formulas, which revealed highly significant differences. The relations among the square value of stress-wave transmission velocity (V_t ² and V_t ²⁾ and MOE, MOR, E _Dl, and E _Dt, respectively, could be represented by positive linear regression formulas. The differences were highly significant.Part of this report was presented at the International Wood Engineering Conference '96, New Orleans, LA, USA, October 1996     

原木截面形状的二次B样条曲线拟合

描述了一种模拟原木截面形状的新方法。用自行研制的MQK3102原木形状识别机测得原木截面上的有限离散样点,利用二次B样条参数曲线拟合方法对这些点进行拟合。该方法能较好地模拟出原木截面的真实形状,样点数量要求不多,计算速度快,前一段曲线的计算结果不影响后面的计算,避免了由累计误差引起的图形失真。将其运用到原木长度方向上的多个采样截面,可近似模拟出原木的整体外形,从而为原木的优化下锯提供参考模型。图4参9。     

Influence of loading point on the static bending test of wood

We conducted three-point bending tests by changing the condition at the loading point and then examined the influence of the loading point on the test data. Yellow poplar (Liriodendron tulipfera L.) was used for the tests. First, using loading noses with various radii, static bending tests were conducted by varying the depth/span ratios. Deflections were measured from the displacement of the cross head and at the point against the loading nose: Young's and shear moduli were obtained from the modified Timoshenko's bending equation proposed in a previous paper. Then a similar testing procedure was undertaken by inserting cushion sheets of Teflon between the specimen and the nose. After the measuring these moduli, bending strengths were measured using the loading noses and cushion sheets. The following results were obtained: (1) When the deflection was measured from the displacement of the cross head, the radius of the loading nose had an influence on the additional deflection when the depth/span ratio was high, causing the dependence of the shear modulus on the radius. In contrast, the radius had little influence on the measurement of Young's modulus. By placing cushion sheets between the nose and the specimen, the effect of the radius was moderated. When the deflection was measured at the point against the loading nose, the radius of the nose had little influence on the additional deflection; hence the loading nose had little influence when obtaining Young's and shear moduli. This tendency was commonly observed regardless of whether the cushion sheets were in place. (2) When the specimen had a high depth/span ratio, the bending strength increased with the increase in the radius of the loading nose. However, the influence of the radius was small when the specimen had a low depth/span ratio. There was no significant effect of the cushion sheets used here on the measurement of bending strength.Part of this paper was presented at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998     

落叶松锯材目测分级与力学性能相关性的研究

以落叶松锯材为试验对象,依据GBS0005—2003《木结构设计规范》中外观分等的相关规则。对人工林落叶松锯材进行了以节子为检量对象的外观分等试验,并对分等后的锯材进行了弯曲破坏试验,分析比较了外观分等结果与其弯曲破坏检测结果的相关关系。     

Effect of fungal exposure on the strength of thermally modified Norway spruce and Scots pine

Abstract

Thermal modification at elevated temperatures changes the chemical, biological and physical properties of wood. In this study, the effects of the level of thermal modification and the decay exposure (natural durability against soft-rot microfungi) on the modulus of elasticity (MOE) and modulus of rupture (MOR) of the sapwood and heartwood of Scots pine and Norway spruce were investigated with a static bending test using a central loading method in accordance with EN 408 (1995). The results were compared with four reference wood species: Siberian larch, bangkirai, merbau and western red cedar. In general, both the thermal modification and the decay exposure decreased the strength properties. On average, the higher the thermal modification temperature, the more MOE and MOR decreased with unexposed samples and increased with decayed samples, compared with the unmodified reference samples. The strength of bangkirai was least reduced in the group of the reference wood species. On average, untreated wood material will be stronger than thermally modified wood material until wood is exposed to decaying fungi. Thermal modification at high temperatures over 210°C very effectively prevents wood from decay; however, strength properties are then affected by thermal modification itself.     

Critical section effect during derivation of settings for grading machines based on dynamic modulus of elasticity

Testing of the critical section between the load points in four-point bending testing is required according to [DIN EN 384:2010–08, Structural Timber – Determination of Characteristic Values of Mechanical Properties and Density (Brussels European Committee for Standardization)]. However, strength grading machines based on measurements of the dynamic modulus of elasticity (MOEdyn) benefit as the strength of the weakest section is not always measured when deriving settings. According to the current procedure for derivation of settings, violation of the critical section requirement is accepted. The extent of such violation and its impact on grading settings of strength classes are quantified in two ways using about 3500 recently tested specimens of Norway spruce: empirically and modelled. The results show that for strength grading machines based on MOEdyn, the settings would be higher if the weakest section was always placed between the inner load points. The current procedure, however, leads to lower settings and hence better yields in practice. The settings for machines based on MOEdyn are up to more than 20% higher if the lowest bending strength of the entire board is applied. To treat different grading principles equally, a correction factor for settings of MOEdyn-based grading machines should be introduced – especially for lower strength classes. A simplified factor between 1.00 and 1.20 for standardization is recommended.     

Evaluation of the Hitman PH330 acoustic assessment system for harvesters

Reductions in Pinus radiata D. Don. (radiata pine) clearfell age have increased the juvenile wood proportion in sawlogs, increasing the need to segregate low modulus of elasticity (MOE) material early in the supply chain to avoid the costly processing of low-value, non-structural boards. In Australian radiata pine plantations, variability in MOE is greater between trees than between stands, requiring tests of individual trees to identify those with low MOE. Time of flight of a sound wave in a tree or log is known to be well-correlated to its MOE. The trial examined the ability of a newly developed acoustic assessment tool, the Hitman PH330 (PH330) supplied by Fibre-gen Limited, fitted to a harvester head, to identify and segregate low MOE sawlogs during a cut-to-length harvesting operation in a radiata pine plantation. The impact of using the tool on the harvester’s productivity was also examined. There was a reduction in the mean productivity of the harvester when using the PH330 compared with normal operations not using the PH330 but it was not significant. Mechanical MOE testing showed that boards cut from sawlogs which the PH330 identified as structural, had significantly greater mean MOE than boards from non-structural sawlogs, demonstrating the PH330 was able to separate high and low MOE sawlogs.