Estimation of the internal shear strength distribution of the element for laminated veneer lumber by nonlinear least-squares method

Until now we developed an estimation method for strength distributions of laminated veneer lumber (LVL) element by nonlinear least-squares method (NLM). Estimated strengths by this method were modulus of elasticity (MOE) and modulus of rupture (MOR) in the horizontal use direction and the vertical use direction, tensile strength and compression strength. But to use LVL for structural members, shear strength was also needed. Therefore, we tried to estimate the shear strength distribution of LVL element by NLM same as MOE and MOR in the horizontal use direction and the vertical use direction, the tensile strength of LVL and the compression strength of LVL in the previous reports. We conducted shear strength test for LVL and estimated element shear strength distribution by LVL strength data in the horizontal and vertical use direction. Next, we simulated LVL shear strength distribution using element shear strength distribution and compared with experimental ones in each use direction. They were overlapped in both use direction. Therefore, we could validate NLM for estimating element shear strength distribution.     

Fire protection of a laminated veneer lumber joint by wood carbon phenolic spheres sheeting

Laminated veneer lumber joints made with metal plate connectors were protected with wood carbon phenolic spheres (CPS) sheeting and tested for creep under fire. The effects of the carbonizing temperature of charcoal, used as raw material for the CPS sheets, the thickness, and the location of the sheet on the joint regarding the fire-resistance performance of the joint were studied. The time to rupture of the joints covered with CPS sheets made from charcoal carbonized at 800°C (CPS800) was slightly prolonged compared with that of uncovered joints. On the other hand, the time to rupture of CPS sheets made from charcoal carbonized at 1600°C (CPS1600) was markedly extended. The changes in the charcoal properties due to increasing the carbonizing temperature might be the main reason the CPS1600 sheets had higher fire-resistance performance. The thickness and location of CPS1600 sheets have significant effects on the fire resistance of the joint. A highly fire-resistant laminated veneer lumber joint was obtained using a CPS1600 sheet. The CPS1600 sheet with a thickness of 3mm covering three sides of the joint prolonged the time to rupture 16-fold compared with that of unprotected joints.Part of this paper was presented at the 4th International Wood Science Symposium, Serpong, Indonesia, September 2002     

Modeling of a cylindrical laminated veneer lumber I: mechanical properties of hinoki (<Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis>) and the reliability of a nonlinear finite elements model of a four-point bending test

The use of low-grade logs to build spirally wound laminated veneer lumber (LVL) has been studied and improved from the point of view of the gluing process, fiber orientation angle, and end joint of the LVL. The butt joint appears to be the fracture point when the column is submitted to a compressive or bending load. Owing to the complexity of cylindrical LVL, we used a finite element method to simulate the mechanical behavior of part of its wall. This part was small enough to be considered flat but was representative of the structure, especially in the area of the butt joint. This allowed us to test the validity of different settings of the parameters involved in the manufacturing process. To feed data for this model, we used the results established for the linear and nonlinear behavior of raw hinoki in Part I of this series of articles. We then used this numerical model to improve the quality of the butt joint by testing different settings of the joint. We show that reducing the butt joint gap under 0.5 mm, which requires only a few changes in the production line, provides an important increase in the modulus of upture and nonnegligible improvement of the modulus of elasticity compared to that for a ≥ 1 mm butt joint gap.     

Development of constitutive model for laminated veneer lumber using digital image correlation technique

This paper describes the development of a three-dimensional constitutive model for laminated veneer lumber (LVL) needed for new developments using this material. The LVL was manufactured in New Zealand from Radiata Pine. Experimental testing has been performed according to European timber testing standards. Block compression testing has resulted in modulus of elasticity values in the three material directions. Digital image correlation (DIC) technique has been used to determine the six Poisson’s ratios. Shear testing, whereby timber specimens were glued between two steel plates, has given stiffness values using DIC measurements. Experimental testing results have been compared with values found in literature. Results from this experimental testing programme have made it possible to create a three-dimensional elastic material model of LVL for the use in finite element analysis programmes. Although the material properties do not result in a symmetrical constitutive matrix, only minor adjustments are needed to gain the benefits of a symmetrical matrix.     

尾巨桉/金属板复合材料层间正应力分布特征的有限元解析

利用三层尾巨桉单板之间嵌入与两张性能相同的金属薄板组成五层尾巨桉单板/金属网层积复合材,并采用预实验优化的热压工艺参数压制成板。采用大型通用有限元分析软件ANSYS10.0构建了尾巨桉/金属网复合材料的有限元数值分析模型,模拟了尾巨桉/金属复合材料界面自由边附近与板材内部界面应力的分布规律,解明了最可能引起分层破坏的正应力的分布规律。主要结果与发现如下:(1)复合材料四层界面处三个正应力的二维应力场分布云图表明自由边附近出现奇异应力的分布特征,自由边处正应力σx的值最大,其最大值为99.72 MPa;(2)复合材料四层界面处三个正应力的三维应力场分布云图表明在四层界面处正应力的应力σx集中现象都最为明显,最大应力集中值可达280.0 MPa。     

Strength properties of laminated veneer lumber in compression perpendicular to its grain

Tests of compression perpendicular to the grain were carried out on laminated veneer lumber (LVL) and timber. The species tested were sugi, radiata pine, karamatsu, akamatsu, and dahurian larch; two sets of sugi specimens were tested, with the sugi LVL products being manufactured in different plants. The strength properties of the materials for different loading directions were compared for LVL and timber. At 5% compressive strain in the same materials, the average stress in the tangential direction of timber was larger than that in the radial direction for all species except for radiata pine, and the average stress in the edge-wise direction of LVL was larger than that in the flat-wise direction for all species except for radiata pine. When the stress at 5% strain was compared in the same direction, the average stress of LVL in the edge-wise direction was larger than that in timber in the tangential direction for all species, but there were no great differences between the average stress of LVL in the fl at-wise direction and that of timber in the radial direction for all species except for radiation pine. There was a close relationship between density and stress at 5% strain in LVL, especially in the edge-wise direction. For all results, radiata pine did not follow the trend of the other species; The large annual ring width of radiata pine was considered to have affected the results.     

Effect of size on the bending strength of laminated veneer lumber

Summary The effect of size on bending strength has been experimentally determined for laminated veneer lumber. Width was found to have no effect on bending strength. The effect of depth times length on bending strength obtained by the slope method was about 0.075, which is in good agreement with the results obtained by the shape parameter method. The effect of length is somewhat more severe than the effect of depth. Size was found to have no effect on modulus of elasticity or modulus of rigidity.In addition, the relationships between bending strength, modulus of elasticity and density of laminated veneer lumber were experimentally modelled.The author is pleased to acknowledge Research and Development Manager Matti Kairi, who represents the Kerto laminated veneer lumber manufacturer of Finnforest Oy, for fruitful co-operation over several years. The patience of senior research scientist Markku Kortesmaa, who calculated and several times explained the details of Appendix A for the author, is also acknowledged     

Fire-resistant performance of a laminated veneer lumber joint with metal plate connectors protected with graphite phenolic sphere sheeting

Creep under fire of laminated veneer lumber (LVL) joined with metal connectors was studied. The fire-resistant performance of LVL butt joints connected with metal plates protected with graphite phenolic sphere (GPS) sheeting was discussed. The GPS sheeting was overlaid on the joint in different sizes and locations. The joint was exposed to a burner with a top flame temperature of 800°C and loaded with a load of 200 N to test for creep under fire. The results showed that the fire-resistant performance of the joint was markedly improved by the sheeting. The size and location of the GPS sheet significantly affected the time to rupture of the specimen, which was six times longer than that without GPS. Temperature measurements at the joint showed that the GPS sheeting distributed the heat along the surface and delayed failure. Thermographic images and analyses clarified the improvement in fire-resistant properties due to GPS.     

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.     

Outdoor exposure tests of structural laminated veneer lumber I: evaluation of the physical properties after six 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 paper is an interim report on the results after 6 years' exposure. Seven kinds of structural LVL with no preservative treatment were subjected to the tests. These specimens were sampled at the testing site each year and then stored for more than 1 year in a testing room conditioned at 20°C and 65% relative humidity. We then measured the modulus of elasticity (MOE) by longitudinal vibration frequency, the penetration depth by the Pilodyn method, weight loss, color difference (E ^*) by the CIEL ^* a ^* b ^* system, swelling, compression strength, and bending-shear strength. Deterioration caused by outdoor exposure was obvious in the color, weight, MOE, and compressive strength of LVLs, but not in the penetration depth by the Pilodyn method or the bending-shear strength. The retention values of MOE and compressive strength after 6 years of exposure were 78% and 77%, respectively. The difference in durability among material species was not significant in general, except that heavy decay by brown rot fungi took place on some of the grand fir specimens. It should be noted that no significant delamination occurred in any of the adhesive layers, although slight checks developed on the surface of the specimens.     

Development of structural composite products made from bamboo II: fundamental properties of laminated bamboo lumber

This experiment explored the technical feasibility of using bamboo zephyr mat with pre-hot-pressed treatment for the manufacture of laminated bamboo lumber (LBL), which is similar in construction to that of laminated veneer lumber (LVL). Six LBL boards (made from four-ply bamboo zephyr mats) with approximate dimensions of 2×42× 42cm were fabricated using resorcinol-based adhesive. The experimental design involved three combinations of layered structures (types I, II, and III) and two LBL loading positions (H-beam and V-beam) during the bending test. These materials were then compared to ordinary LVL. Results indicated that the bending properties (moduli of rupture and elasticity) of LBL were comparable to those of LVL, but there was no significant effect on the physical and mechanical properties among the three types of LBL beam. Interestingly, orienting the glue line to the vertical direction (V-beam) could maximize the ultimate strength of the LBL.Part of this research was presented at the 49th Annual Meeting of the Japan Wood Research Society, Tokyo. April 1999, and at the Pacific Timber Engineering Conference, Rotorua, New Zealand, March 1999     

Modeling lumber yield of white spruce in Alberta,Canada: a comparative approach

Estimation of lumber yield from a forest inventory is important in determining the optimal utilization of available regional wood supply. In this study, we review existing approaches of lumber yield estimation, including knowledge-based empirical board-foot log rules used in the United States and some regions of Canada, survey-based wood conversion factors, and optimization technology-based computer simulations. Lumber yields estimated from different approaches are then compared using six datasets from a white spruce commercial thinning experiment in Alberta, Canada. Our results indicated that (1) estimated lumber yield can be significantly different when different methods are employed; (2) board-foot log rules often underestimate lumber yield; (3) wood conversion factors represent regional average of lumber yield as a constant and thus are unsuitable for forest inventory-based lumber yield estimation; and (4) optimization technology-based computer simulations can provide the best estimate of lumber yield for a given forest inventory as long as the mill conditions and lumber dimensions from market demand are specified. Forestry investment in applying computer simulation methods should be encouraged in sawmill operations to improve lumber yield and enhance environmental protection, because, for a given amount of lumber, improving lumber yield means reduced demand for harvest operations.     

Sensitivity study of the finite element model for wood-framed shear walls

A sensitivity study was performed with a nonlinear elastic finite element model for monotonie analyses of wood-framed shear walls. The objective was to provide information about simplifying a model of wood-framed shear walls with no significant loss in accuracy. The simplifications concern features such as slips in joints between frame members, slips in hold-down connections, and bearing between adjacent sheathing panels. The results from analyses of a shear wall with an opening of window shape show that the effect of constraint by the bearing between sheathing panels and slips in frame joints on the overall stiffness of the wall is limited. Thus, there are great possibilities for reducing the calculation time by not taking these phenomena into account, avoiding an excessive number of degrees of freedom and iterations. The influence of the simplifications on the distribution of vertical reaction forces along the wall is more significant. Furthermore, if each simplification is introduced separately, the effect on the overall stiffness is greater. The difference, however, is less than 10%. The failing pattern of the nail connections is also clearly influenced by the simplifications when they are introduced separately. The results from the analyses show that slips in frame joints can be sufficiently represented by those in connection with the opening.     

Modeling dominant height growth based on nonlinear mixed-effects model: a clonal Eucalyptus plantation case study

Eucalyptus is the most valuable cultivated forest genus in Brazil nowadays. Modeling eucalypts growth has been a challenge for foresters in recent years due to the strong site and genetic variations, management regimes and multiple products generated from those plantations. Because the forest height growth is directly related with the site characteristics and with forest productivity, the improvement on the height growth representation implies in better productivity estimation. A nonlinear mixed-effects model was developed to represent the height growth pattern of eucalypts clonal stands from the Brazilian coastal region. Likewise in other scientific fields, this type of modeling methodology showed to be flexible, precise and accurate, generating multimorphic growth curves for different sites and clones.     

Ultrasonic treatment to improve the quality of recycled pulp fiber

The effect of ultrasound on the quality of recycled fibers was investigated. Ultrasound was applied to recycled pulp fiber suspension before ink removal by conventional flotation. The ultrasonic treatment induced an increase in the sedimentation volume of the fiber, which implies that the flexibility and bulkiness of the fiber increase. The water retention value of the ultrasonically treated fiber recovered from the loss caused by the recycling. These facts are due to a beating effect of the treatment. The paper sheets prepared from the ultrasonically treated fiber suspension showed higher sheet density, tensile strength, and brightness than that from an untreated fiber suspension. The process, which consists of ultrasonic treatment for 1 min following flotation deinking, requires about 1.4 times as much energy as the conventional flotation deinking process, but it induced 20% improvement in brightness. The results indicate that the ultrasonic treatment is effective in improving recycled fiber quality.This report was presented in part at the 48th Annual Meeting of the Japan Wood Research Society, Shizuoka, April 1998; and at the 5th Annual Meeting of the Japan Cellulose Society, Kyoto, July 1998     

Development of a joint system using a compressed wooden fastener II: evaluation of rotation performance for a column-beam joint

In the present study, a plate and a doweled fastener made of compressed wood (CW) were newly introduced into a moment resisting column-beam joint system for a small portal frame structure. A mechanical model that contains not only an axial spring, but also a rotational spring, considered resistant factors to verify how each element resists rotation. Theoretical performance was compared with experimental data. Consequently, the mechanical model was shown to be suitable and the combination of resisting factors was found to be very effective; i.e., the rotational spring provides more influence on the stiffness and moment compared with the axial spring. Large moment and ductility can be achieved by virtue of the high embedding performance of the CW plate in the rotational spring, accompanied with the high shearing performance of the CW dowel in the axial spring.     

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.