Structural Lumber Research Articles

The Adhesion Performance in Green-Glued Finger Joints Using Different Wood Ring Orientations

Structural lumber is designed to meet the technical standards that ensure safety, cost-effectiveness, and sustainability. However, some tree species face limitations in their growth, which restricts their widespread use. An example of this is Nothofagus alpina, which has excellent mechanical properties but is not utilized much due to the challenges in extracting its timber and poor utilization, mainly because of the length of the wood. There is little information concerned with the uses and better management of small pieces using Nothofagus species, but it is still insufficient. This study investigates the adhesion performance of green-glued finger joints with varying wood ring orientations and moisture contents ranging from 21% to 25% using Nothofagus alpina. The primary aim is to assess how ring orientation and wet timber affect the green gluing process for creating larger wood pieces than sawn wood. The resulting products could meet the standards for wood serviceability number three for native Chilean wood. The findings indicate that finger joint performance improves with higher timber moisture levels. However, the orientation of the wood fibers did not significantly affect the performance under the tested conditions. It is important to note that this effect may become more significant near the fiber saturation point. These findings emphasize the need for a detailed protocol on the green gluing technique for Nothofagus alpina and the associated drying and surface processes in finger joint construction.

Reverse-cyclic performance of United States prescriptive code connectors in a novel mass timber structural composite panel

Mass timber has been recently increasing in popularity, especially panel products such as cross-laminated timber (CLT), which has spurred innovation in creating new mass timber materials. One recent mass timber material utilizes structural composite lumber to create a PRG-320 compliant CLT, referred to as a structural composite panel (SCP). To increase the knowledge on the connection performance of the new SCP, reverse-cyclic testing was conducted on standard mass timber panel prescriptive connection systems within U.S. codes with SCP as the substrate. Three different types of tests were conducted: shear tests of a floor-to-wall connector, uplift tests of the same floor-to-wall connector, and shear tests of an inter-panel connector. Two monotonic and six reverse-cyclic tests were done per test configuration. The connections typically failed through a combination of wood failure and either nail bending and withdrawal or nail fracture. Two cyclic tests of the floor-to-wall connector in shear and all tests of the floor-to-wall connector in uplift failed through fracture of the plate connection. Results were compared to previous testing on CLT that was used to validate the connection and design methodology. Higher maximum strengths were observed when comparing the SCP to previously tested CLT, with an average increase of 20 percent. The displacement at maximum force and ultimate displacement capacity were similar between the SCP and previous CLT connections. Connections in SCP exhibited a lower stiffness than comparable CLT specimens for all tests, with an average difference in stiffness of 33 percent. This led to a comparatively lower ductility for the SCP specimens than for the CLT. ASCE 41 trilinear parameters were derived for all cyclic tests to aid in the utilization of the connections with this new material.

Erratum to: Evaluation of Adhesive Characteristics of Mixed Cross Laminated Timber (CLT) Using Yellow Poplar and Softwood Structural Lumber

Erratum to: Evaluation of Adhesive Characteristics of Mixed Cross Laminated Timber (CLT) Using Yellow Poplar and Softwood Structural Lumber

MECHANICAL PROPERTIES OF LAMINATED BAMBOO LUMBER MADE OF TROPICAL SPECIES

Bamboo has been the trend for a sustainable material, due to its renewability. Bamboo can grow abundantly throughout the tropical area of the world, such as Latin America, East Asia and Southeast Asia. It is seen that Southeast Asia has variety of bamboo to utilize and many of them are suitable for structural applications. One additional reason is that they are clumping type, so fibers are built stronger. Bamboo is hollow and irregular in sizes and shapes, so it cannot maximize the use out of the materials. Bamboo Laminated Lumber (LBL) is the product to solve bamboo issues on the irregularity be transforming into solid lumber. It can be called the engineered bamboo, which have been transformed conventional form of bamboo using engineering process. This is the same technology as laminated timber. It has more potential to substitute the use of timber. This research is to experiment of making LBL using structural bamboo species that are widely used in Southeast Asia. They are Dendrocalamus Asper, Dendrocalamus Sericeus, Bambusa Multiplex, and Bambusa Blumena. They are tested for mechanical properties; Tension, compression parallel to grain, compression perpendicular to grain, and bending. Those properties are compared to other tropical hardwood and engineered wood. The result shows that LBL of all species are qualified for medium-hardwood quality, while B.Multiplex lumber performs best overall. The rest still have great mechanical properties and can be qualified some structural lumber in order to reduce the use of timber.

Machine Vision for Knot Detection and Location in Chinese Fir Lumber

Abstract In order to be utilized in the design of a wood building, the lumber must pass grade. Machine-vision inspection grading offers higher efficiency and accuracy than traditional manual visual grading. In this paper, a fast and accurate method for identifying defects in large-size structural lumber based on machine vision of Fujian Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) constructional lumber (FCF CL) is proposed. Specifically, the grey matrix of the captured images on the surface of the sawn timber is initially scanned and the pixel weights on the edges of the image greyness variables are calculated. A matrix-valued torus was formed by fitting the knot edge profile and analyzing changes in the gradient values at the knot's edge, as well as calculating the directional derivative's rate of change. The knot three-dimensional mapping curves were projected onto the plane to form horizontal rise contours. Observe from the contour map of the whole large-size sawn timber, and extract the positional information of the knot where there is a trough (groove). The test results show that the rRMSE (Relative Root Mean Square Error) measured at the x axis position of knots is within 0.49 percent; the rRMSE measured at the y axis is 0.35 percent, which has high detection accuracy and meets the production requirements. We also investigated the effect of knots in different positions on the modulus of elasticity and the bending strength of FCF CL, with a view to establishing a link between machine-vision knot detection and mechanical properties of sawn timber in our next work.

Environmental impacts of structural lumber production in Japan

Low-rise buildings in Japan are predominantly made of wood. Furthermore, the government promotes the use of wood in mid- and high-rise buildings to tackle climate change. Therefore, the environmental impact of structural lumber should be assessed. In this study, we evaluated greenhouse gas (GHG) emissions and resource consumption associated with structural lumber production using life cycle assessment. Herein, we focused on Japanese Agricultural Standard certified structural lumber (artificially dried lumber and machine-grade structural lumber) made from Japanese roundwood. To ensure representativeness, 15 companies and 15 sawmills covering more than 50% of Japan's structural lumber production were selected and data on their production were collected. The results show that the GHG emissions and resource consumption of Japanese structural lumber are 7.99 × 10 kg-CO2e/m3 and 1.77 × 10–3 kg-Sb eq./m3, respectively. The major sources of GHG emissions are electricity and roundwood production. Roundwood and metal tools significantly affect resource consumption. The recycling of rare metals in tools is essential for reducing resource consumption. A significant amount of heat energy is utilized for drying, and this heat energy is supplied from both biomass and fossil fuels. GHG emissions and resource consumption are 5.3 and 1.6 times higher, respectively, if biomass fuel is replaced by fossil fuel. Policies supporting the introduction of biomass boilers have been highly effective. It is recommended to further promote measures such as replacing fossil fuel-based boilers with biomass boilers and effectively utilizing biomass boilers in multiple regional sawmills. In addition, switching from grid electricity to electricity generated by renewable energy sources is effective for further reducing environmental impacts. The long-term use of structural lumber is valid for combating global warming because it fixes carbon for decades. In this study, the CO2 emissions from biomasaluated in terms of carbon neutrality. Appropriate forest management is a prerequisite for carbon neutrality, and the promotion of sustainable forest management, such as reforestation after logging, is crucial.

Prediction of withdrawal resistance of self-tapping screws in softwood structural lumber

The withdrawal resistance of self-tapping screws (STS) in Korean structural softwood in the vertical fiber direction was examined. Four representative softwood species were selected based on their specific gravity. Three STS fastener diameters were used for an STS penetration depth of 50 mm. The withdrawal capacity tended to increase with the specific gravity of the specimens and as the diameter of the STS increased. Primarily, the difference in strength was maximized as the STS diameter increased from 8 to 10 mm. Predictive experimental equations were proposed based on the experimental values of the relationship between the specific gravity of the structural material and the withdrawal resistance according to the diameter of the STS. The values were compared with the predicted values calculated using fastener and screw prediction equations proposed by the National Design Specification for Wood Construction (NDS) and European Standards (EN). The results calculated using the NDS prediction equations yielded a peak difference of 43% compared with the experimental withdrawal capacity, whereas the EN prediction equations yielded a difference of 0.7 to 1.14 times the experimental values. The ratios between the withdrawal capacity predicted by the proposed prediction equations and the experimental withdrawal capacity were the most similar, ranging from 0.80 to 1.15.

Impact of Growth Characteristics on Properties of 2 by 8 Southern Yellow Pine Structural Lumber

Abstract Southern pine is one of the most important softwood resources in the United States, and the majority of southern pine is for lumber production, more specifically for construction. The lumber used for construction is required to meet strength-specifications as a method of ensuring the strength values within different classes. Most of the southern pine lumber is visually graded, which is based on knot, slope of grain, and wane. However, the presence of pith is not included in the visual grading system. The presence of pith indicates presence of juvenile wood, which has a negative effect on mechanical properties. The objective of this study was to evaluate the effect of pith on rings per inch, percentage of latewood, modulus of elasticity (MOE), and modulus of rupture (MOR) in 292 samples of southern pine No. 2 2 by 8 lumber. Lumber without pith had significantly greater MOE (11.1 vs. 10.0 GPa), MOR (39.7 vs. 36.4 MPa), and specific gravity (12% moisture content [MC]; 0.55 vs. 0.52) than did lumber with pith. The results show that the presence of pith is an important factor that can improve lumber grading, and it could be included in the visual grade system.

Producing structural grade hardwood lumber as a raw material for cross-laminated timber: Yield and economic analysis

The economic feasibility of producing structural-grade hardwood lumber (SGHL) that qualifies as a raw material for structurally rated cross-laminated timber (CLT) was examined. 126 yellow poplar logs from diameters 12 to 15 inches were selected and divided into test and control samples. A log yield study was then conducted of the yield and revenue generated when producing lumber graded with National Hardwood Lumber Association (NHLA) rules, SGHL rules, and a mix of both rules (NHLA and SGHL-graded lumber). Producing mix-grade lumber added approximately 27% more revenue than producing NHLA-grade lumber on average if sawmills adopt a cant sawing method. Mix-grade lumber production resulted in 32% of the total volume produced as SGHL and the remaining 68% as NHLA lumber. As a result, 2 Common and lower-grade lumber board footage was reduced to only 29% in test samples and remained converted into SGHL compared to more than 85% of 2 Common and lower-grade lumber boards for control samples. 95% of the SGHL produced as mixed-graded lumber with NHLA-grade lumber met the specifications required to produce structural CLT, and the remaining 5% can be utilized to produce non-structural grade CLTs if they meet the minimum requirement of the materials for CLT production.

Performance Evaluation of Manually-Operated Gmelina Fruit Mechanical Depulping Machine

Gmelina tree has been used in revegetation program of the government and for production and utilization of quality wood, structural lumber, plywood, agricultural implements, furniture and even artificial limbs. The fastest way to grow seedlings is through the seeds that can be found in its fruits done by trampling with feet or setting the fruits on the concrete road, run over by vehicle tires. The purpose of these research was to evaluate the performance of the developed utility model for gmelina depulping for community utilization to maximize seeds retrieval, reduce time wastage and provide safety to children of farmers commonly assigned to gather and retrieve seeds in the roadside. Gmelina depulper with Utility Model IPOPhil registration no. 2-2016000797 was fabricated and utilized in the study. Fresh Gmelina fruits, soaked fruits for one (1), two (2), and three (3) days in water were used as materials in the evaluation of the depulping machine. Test trials using 20 fruits/trial and average of 25 seconds test duration per trial revealed that the depulping machine input capacity was 43-50 fruits/minute and recovery rate of 87%. There was no significant difference on depulping capacity and recovery rate with fresh fruit and soaking it for 3 days before depulping. The production cost of one unit was Php. 9,275.00 which could be recovered using 1,855 seedlings sold at Php 5.00 each. It was recommended to depulped gmelina fruits without soaking, fabrication of unit with bigger hopper intended for large gmelina fruits size to increase recovery rate and reduce the percentage of damaged seeds.

Modelling the influence of radiata pine log variables on structural lumber production

We run logit models to explain the variability of Pinus radiata structural lumber in 71 second and third unpruned logs. The response variable was the proportion of lumber with a static modulus of elasticity greater or equal than 8000 MPa, pMSG8+, and the explanatory variables were log volume, branch index, largest branch, log internode index, wood basic density, and acoustic velocity. The average pMSG8+ volume was 44,30 % and 36,18 % in the second and third log respectively. Ten models were selected based on meeting statistical assumptions, their goodness of fit, and the statistical significance of their parameters. The best models (R2 - adj. > 0,75) included acoustic velocity (AV) as explanatory variable, which explained 56,25 % of the variability of pMSG8+. Models without AV presented goodness of fit ranging from 0,60 to 0,75 (R2 - adj.), and variables with the highest weight to explain the variability of pMSG8+ were volume, followed by wood basic density, branch index, and largest branch. It is possible to model pMSG8+ from log variables even when acoustic velocity is not available; however, this requires wood basic density models calibrated for the Pinus radiata growing zone.

The Dimensional Stability and Bonding Performance of Hybrid CLT Fabricated with Lumber and COSB

The differences of physical and mechanical properties of different laminations, such as softwood, hardwood or other structural composite lumber, in hybrid cross-laminated timber (HCLT), lead to their dimensional stability and bonding performance more complex than generic cross-laminated timber (CLT). In this paper, the spruce-pine-fir (SPF) dimension lumber and construction oriented strand board (COSB) were employed to fabricate HCLT. The effects of four configurations and three adhesives on the dimensional stability and bonding performance of CLT and HCLT were evaluated in term of the water absorption (WA), thickness swelling (TS), block shear strength (BSS), wood failure percentage (WFP) and rate of delamination (RD). The results showed that with the increase of the COSB laminations, the WA of HCLT specimens decreased, and the values of TS, BBS and WFP increased. The configuration had a significant influence on the dimensional stability, BBS and WFP of the specimen. The adhesive had a significant influence on the dimensional stability and some bonding performances of the specimen. The phenol resorcinol formaldehyde (PRF) specimens had the lowest average RD value compared with the one-component polyurethane (PUR) and emulsion polymer isocyanate (EPI) specimens. Failures were prone to occur in the middle of the thickness of COSB lamination during block shear and delamination tests. The outcome of this paper could help the engineering application of HLCT.

Experimental Study of Bending and Bearing Strength of Parallel Strand Lumber (PSL) from Japanese Larch Veneer Strand

This study examined the structural performance of experimental parallel strand lumber (PSL) from a Larch veneer strand. The prototype of PSL from a Larch veneer strand was manufactured in the experimental laboratory and tested. The bending and dowel bearing strength were determined from the modulus of elasticity (MOE), modulus of rupture (MOR), and dowel bearing strength based on a 5% offset yield load. The test results indicated that the average MOR of PSL was higher than that of 2 × 4 dimension lumber, and the average MOE of PSL was lower than that of 2 × 4 dimension lumber. A linear relationship was observed between the MOR and MOE. The allowable bending stress of PSL was derived as specified in ASTM D2915 and compared with other research. The dowel bearing strength of PSL in parallel to the grain was approximately double that perpendicular to the grain of PSL. A comparison of several theoretical calculations based on each national code for the dowel bearing strength was conducted, and some theoretical equations produced results closer to the experimental results when it was parallel to the grain, but the difference was higher in the case perpendicular to the grain. The test results showed that PSL made with Japanese larch veneer strands appeared to be suitable for a raw material of structural composite lumber (SCL) appeared to be used as a raw material for SCL.

Flexural properties of visually graded southern pine 2×4 and 2×6 structural lumber

Flexural properties of visually graded southern pine structural lumber were evaluated. Several grade controlling characteristics were considered relative to bending properties and compared with current design values. A total of 751 southern pine lumber specimens were obtained from a broad spectrum of regions in the southeastern United States. Visually graded No. 2, nominally two inch thick specimens, in four and six inch widths, were obtained from commercial sawmills. All specimens were evaluated by a certified grader in the laboratory. Actual dimensions, weight, and moisture content (MC) were measured. Growth and manufacturing related characteristics were identified and classified into two categories: strength reducing characteristics (SRC) and grade reducing characteristics (GRC). Specific gravity (SG), bending modulus of elasticity (MOE), and modulus of rupture (MOR), were determined for each specimen. The presence of knots was identified as the most significant SRC; their presence had the most significant impact on SG, MOE and MOR. For GRC, specimens with knots, warp and specimens that fell into the category none, were significantly lower in SG, MOE and MOR. MOE and the allowable design bending strength values yielded in this study met the current design value criteria for both widths tested.

Challenges Facing the Development and Market Introduction of Hardwood Cross-Laminated Timbers

Abstract The interest in softwood-based cross-laminated timber (CLT) production has in turn generated a great deal of interest in producing CLT from hardwood species. This prospect of a new market for hardwood lumber is a significant driver behind efforts to gain certification of hardwoods within American Panel Association (APA) PRG 320, Standard for Performance-Rated Cross-Laminated Timber. However, a number of challenges present significant hurdles for gaining acceptance of hardwoods in CLT manufacturing. These include differences in how softwoods and hardwoods are produced and marketed (e.g., structural lumber markets [softwoods] vs. appearance-grade markets [hardwoods]), lumber grading differences, available sizes of hardwood lumber, drying differences between hardwoods and softwoods, and gluing particularities with hardwoods. This paper identifies the various issues involved with introducing hardwoods into a softwood-dominated market and what it will take to be competitive within the overall CLT market.

Demonstration Project Reporting Detection of Subterranean Termite (Blattodea: Rhinotermitidae) Infestation and Spray Polyurethane Foam

Demonstration Project Reporting Detection of Subterranean Termite (Blattodea: Rhinotermitidae) Infestation and Spray Polyurethane Foam

Evaluation of Low-Grade Yellow-Poplar (Liriodendron tulipifera) as Raw Material for Cross-Laminated Timber Panel Production

Abstract Utilization of low-grade yellow-poplar (Liriodendron tulipifera) lumber would provide for alternative structural lumber sources and promote the growth of cross-laminated timber (CLT) manufacturing facilities within the Appalachian Region. A significant amount of low-grade yellow-poplar lumber (i.e., National Hardwood Lumber Association [NHLA] No. 2A and Below Grade) is utilized for wood pallets. In practice, this material is not graded for structural purposes. Additionally, research on yellow-poplar for structural use has focused on grading lumber from a small population of selected logs, not by regrading NHLA lumber from manufacturing facilities. Therefore, the research's objective was to investigate the structural grades of a typical population of NHLA graded No. 2 and lower lumber and evaluate their potential to meet structural grades necessary for CLT panels. NHLA graded lumber was regraded and assigned to visual structural grades following Northeastern Lumber Manufacturers Association rules and evaluated for flatwise bending modulus of elasticity (MOEb) by nondestructive proof loading. The results of the study indicated that 54.6 percent of the boards possessed a minimal structural visual grade required for CLT panels according to American National Standards Institutes/The Engineered Wood Association (ANSI/APA) PRG 320-2019 (2020). Splits were the most common limiting defect that downgraded boards to nonstructural grades. Also, 96.6 percent of the boards evaluated had a MOEb above the required minimal board value of 1.2 ×106 psi (8,274 MPa) listed in ANSI/APA PRG 320-2019 (2020). The results of the study indicated that a majority of NHLA low-grade yellow-poplar, when regraded for structural purposes, meets or exceeds minimum lumber grade values necessary for use in CLT panel production.

Low-cycle fatigue life and duration-of-load effect for hybrid CLT fabricated from lumber and OSB

Given the nature of cross-laminated timber (CLT), with an orthogonal arrangement and rolling shear characteristics of transverse layers, it has a more complex duration-of-load (DOL) effect than other engineered wood products, such as glued-laminated timber. Developing hybrid CLT (HCLT) with structural composite lumber, which can improve the mechanical properties and material sources of CLT, is gaining increasing interest. Construction oriented strand board (COSB) and spruce-pine-fir (SPF) dimension lumber were used to fabricate HCLT specimens for this study. The regular SPF CLT and HCLT specimens having different lay-ups and numbers of layers were subjected to low-cycle fatigue bending and shear loading tests. The Foschi and Yao damage accumulation model was calibrated using the test results. The DOL factors for the CLT and HCLT specimens were calculated using the stress ratio evaluation method. Results showed that the primary failure modes for the fatigue test specimens were the same as those observed in previous short-term ramp loading tests, and a good fit was observed between the model's predictions and the test data. The DOL factor corresponding to a load duration of 50 years, for a three-layer shear CLT specimen, was determined to be 0.53, which was lower than that recommended in CSA O86-19. The fatigue life and long-term performance of CLT were improved by using COSB panels as CLT layers. The HCLT specimens that used COSB only as the transverse layer showed advantages in fatigue life, long-term performance, and practical applications.

Раскрой круглых сортиментов с ядровой гнилью на конструкционные пиломатериалы

Softwood lumber is widely used for the manufacture of load-bearing structures. However, the quality of round timber for lumber manufacturing has been deteriorating recently. The average diameter of round timber entering sawmills is constantly decreasing, and heart rot is common in large-diameter round timber. This is due to the fact that more and more conifers in the forest are being affected by heart rot. The rot infestation is related to the deterioration of the ecological situation caused by environmental pollution. As a rule, the removal of rot occurs at the stage of round timber harvesting. Therefore, during harvesting, most of the wood with heart rot continues to remain in the forest. In addition to littering the area, it continues to infect sound wood. At the same time, together with the wood affected by rot, the sound sapwood, which has good strength characteristics, is also removed. A method for processing round timber with heart rot into elements of load-bearing structures is proposed. In particular, a technological scheme for manufacturing I-beams from such timber has been developed for low-rise house construction. Corner elements are produced as a result of cutting round timber and removing heart rot by milling. The corner elements are dried in clamped state using special devices. Then they are glued together to obtain beams with a cross-section in the form of an I-beam. A set of equipment for the processing round timber with heart rot was selected. The paper presents the results of calculating the costs for organizing the production. The effectiveness of the technological project is evaluated using the method of discounted cashflows by the following indicators: net present value, profitability index, and discounted payback period. The assessment results confirm the effectiveness of the production organization of load-bearing structures made of round timber affected by heart rot. The processing of wood that remains in the forest into elements of building structures not only increases the wood reserves for construction, but also creates conditions for improving the ecological situation in forest areas. For citation: Toropov А.S., Byzov V.Е., Toropova Е.V., Sergeevichev А.V., Sazanova E.V. Cutting of Round Timber with Heart Rot to Structural Lumber. Lesnoy Zhurnal [Russian Forestry Journal], 2021, no. 6, pp. 160–172. DOI: 10.37482/0536-1036-2021-6-160-172

Modeling of radial variations in wood properties and comparison of juvenile and mature wood of four common conifers in Mongolia

Abstract Pinus sylvestris L., Pinus sibirica Du Tour, Picea obovata Ledeb., and Larix sibirica Ledeb. are important forest tree species in Mongolia. The radial variations of wood anatomical characteristics, physical and mechanical properties were evaluated by linear or nonlinear mixed-effects models for effective wood utilization of those of conifers. Many of these wood properties either increased or decreased from the pith to the bark and then became nearly constant based on the selected models. The properties of mature wood were estimated by nonlinear mixed-effects models, suggesting that P. sylvestris and L. sibirica are suitable as structural lumber, P. sibirica can be used for furniture and other interior products, and P. obovata is suitable for structural lumber as well as for furniture or interior products.