Search Results (40)

This study focuses on the development of lignin-based carbon-fiber-reinforced laminated veneer lumber (LVL) beams for garden timber structures, addressing wood shortages and environmental concerns. The research consisted of three main phases: the extraction and characterization of the lignin from corn stalks; the preparation and characterization of lignin-based carbon fibers; the fabrication and testing of reinforced LVL beams. Lignin was extracted from corn stalks using a deep eutectic solvent, followed by the preparation of lignin-based carbon fibers through electrospinning. These carbon fibers were integrated with poplar veneers to create reinforced LVL beams. The test results demonstrated significant improvements in mechanical properties, with the reinforced LVL beams exhibiting a 17% increase in elastic modulus and a 30% enhancement in flexural strength compared with conventional LVL beams. Notable improvements were also observed in tensile strength, compressive strength, and shear strength. This research provides a novel approach for producing high-value-added carbon fibers from agricultural waste, advancing the development of sustainable building materials. Full article

Laminated Veneer Lumber (LVL) presents an alternative material for offshore wind turbine towers and blades for an energy sector whose greenhouse gas emissions are substantial. In compliance with AS/NZS 4536, this case study facilitates a specifications’ selection framework that embraces a validated, cost–benefit determination via life cycle cost analyses (LCCA) specification comparisons. A structured consultation with three key Western Australian offshore industry experts, compliant with a standard phenomenological qualitative approach, further facilitates offshore wind turbine (OWT), LCCA cost comparisons between traditional steel and fibreglass components and LVL wooden components. LVL is found to have a higher capital cost but can generate long-term savings of AUD 30,400 per comparable unit less than Traditional OWT specifications, noting a 5% lower LVL operation and maintenance cost. Where decommissioning recycling facilities exist, OWT LVL specification components are encouraged. This work argues that LVL options uptake in Western Australia (WA) is both practicable and whole-cost effective. Full article

Due to the development of wooden construction as an ecological alternative to brick construction with a high carbon footprint, there is increasing interest in materials such as plywood and LVL (Laminated Veneer Lumber). These engineered wood products have many advantages compared to wood, such as a more uniform distribution of bending, shear, tensile, and compressive strength. However, they require improvements in fire and biological resistance. The flammability of wood and wood composites is a challenge that will allow these materials to stand out as structural or finishing materials. During combustion, toxic gases may be released, which can be harmful to people and the environment. Therefore, it is crucial to clarify whether fire-resistant wood materials are truly resistant to fire and non-toxic in fire conditions. On the other hand, flame retardants should not reduce the mechanical parameters of panels. This work analyses the current requirements (standards) regarding plywood intended for construction and the existing flame retardants for plywood and LVL based on the latest reports in the literature. We then propose an original method for evaluating future chemicals. Additionally, methods for assessing the flame retardancy of plywood and LVL based on the latest reports in the literature are described, and an original method for assessing flame retardancy methods is proposed. Full article

This study outlines a method of utilizing the finite element method and a simple mathematical model to predict the behavior of laminated veneer lumber (LVL) beams strengthened with composite sheets. The numerical models were created using the Abaqus 2017 software. The LVL was considered as a linearly elastic or elastic–plastic material, factoring in Hill’s yield criterion. The composites were simulated as linearly elastic–ideally plastic materials. The mathematical models were predicated on the methodology of transformed cross-section. The theoretical and numerical outcomes were juxtaposed with previous empirical investigations. The comparison encompassed load-bearing capacity, stiffness, and deformation under peak force. Furthermore, presentations of normal stress maps in the LVL and composite have been illustrated. The derived maps were juxtaposed with the delineations of failure modes. An adequate correlation was identified between the theoretical, numerical, and empirical values in the case of beams reinforced with aramid, glass, and carbon sheets. The relative deviation varied from several to multiple percentages. This technique is not applicable for evaluating load-bearing capacity and deformation when only dealing with sheets with low elongation of rupture. This is a consequence of their premature failure. The proposed models may be utilized by researchers and engineers in the design of reinforcements for timber structures. Full article

Among the many benefits of implementing numerical analysis on real objects, economic and environmental considerations are likely the most important ones. Nonetheless, it is also crucial to constrain the duration and space necessary for conducting experimental investigations. Although these benefits are clear, the applicability of such models must be appropriately verified. This research subjected validation of numerical models depicting the behavior of unstrengthened and strengthened laminated veneer lumber (LVL) beams. As a reinforcement, a carbon fiber reinforced polymer (CFRP) sheet and laminates were used. Experiments were conducted on full-scale members within the framework of the so-called four-point bending testing method. Numerical simulations were performed using the Abaqus software. Two types of material models were examined for laminated veneer lumber: linearly elastic and linearly elastic–perfectly plastic with Hill’s yield criterion. A distinction was made in the material properties of carbon composites based on their location on the height of the cross-section. The outlined numerical models accurately depict the behavior of real structural elements. The precision of predicting load-bearing capacity amounts to a few percent for strengthened beams and a maximum of eleven percent for unstrengthened beams. The relative deviation between numerical and experimental values of bending stiffness was at a maximum of seven percent. Applying the elastic–plastic model enables accurate representation of the load versus deflection relation and the distribution of stress and deformation of strengthened beams. Based on the findings, directives were provided for further optimization of the positioning of composite reinforcement along the span of the beam. Reinforcement design of existing laminated veneer lumber members can be made using presented methodology. Full article

123 withdrawal tests were conducted to investigate the change in axial stiffness of fully threaded screws under axial loading and up to four loading cycles. The screws were initially loaded in two cycles within the elastic range, followed by two cycles up to 90% of the characteristic load-carrying capacity. Several parameters relevant to construction practice were varied. The angle between the screw axis and the grain ranged from 30° to 90°, the timber material was varied between glued laminated timber (glulam) and laminated veneer lumber (LVL) made of beech, and the screw diameter ranged from 8 mm to 12 mm. The test results indicate that axial stiffness increases upon reloading compared to the initial loading. On average, axial stiffness increases by 11% between the first and second loading and remains at this level during unloading and further load cycles. However, if the load exceeds the linear–elastic range, the axial stiffness is reduced due to plastic deformation. A comparison with tests on the composite axial stiffness of fully threaded screws in glulam shows that even with a different test setup and testing objective, there is a slight increase in axial stiffness from the first to the second load cycle in the range of 4 to 8%. Full article

Analyzing the feasibility of reinforcing new and existing wooden structures is a valid problem, being the subject of numerous scientific papers. The paper presents the preliminary results of a study on reinforcing Laminated Veneer Lumber (LVL) panels with composite materials bonded to exterior surfaces using epoxy resin. Glass-Fiber-Reinforced Polymer (GFRP) sheets, Carbon-Fiber-Reinforced Polymer (CFRP) sheets, and Ultra-High-Modulus (UHM) CFRP sheets were used as reinforcement. The variables in the analysis were the type of reinforcement and the number of reinforcement layers. The tests were carried out on small samples (45 × 45 × 900 mm) subjected to the so-called four-point bending test. Reinforcement positively affected the mechanical properties of composite section. The highest increases in load bearing were 37 and 48% for two layers of GFRP and CFRP, respectively. The bending stiffness increased up to 53 and 62% for two layers of CFRP and UHM CFRP, respectively. There was a change in failure mode from cracking in the tension zone for unreinforced beams to veneer shear in the support zone (for CFRP and GFRP sheets) and sheet rupture (UHM CFRP). Good agreement was obtained for estimating bending stiffness with the presented numerical and mathematical model; the relative error was up to 6% for CFRP and GFRP and up to 20% for UHM CFRP. This preliminary study proved the effectiveness of combining LVL with FRP sheets and indicated their weak spots, which should be further analyzed to improve their competitiveness against the traditional structures. The key limitation was the shear strength of LVL. Full article

Timber architectures have arisen as sustainable solutions for high-rise and long-span buildings, assisting in implementing a circular economy. The creep strain dissipation of laminated veneer lumber (LVL) was investigated in this work to understand the inherent creep behaviors of LVL derived from natural wood. The results demonstrated a significant loading regime dependency of the creep behaviors of LVL. Coupled creep strain dissipation that transits/is parallel to the wood–adhesive interface was proven in the creep deformation of flat-wise and edge-wise bent LVL. In contrast, the creep strain dissipated considerably along the wood–adhesive interface when the LVL was subjected to axial compression creep. Further investigation into the morphologies of LVL after creep revealed that direct contact between the loading plane and wood–adhesive interface could be a plausible trigger for the accelerated deformation and the resultant plastic deformation of the LVL after creep. We believe that this work provides essential insights into the creep strain dissipation of LVL. It is thus beneficial for improving creep resistance and assisting in the long-term safe application of LVL-based engineered wood products in timber architectures. Full article

In this paper, the results of dynamic laboratory tests of four laminated veneer lumber (LVL) slabs of different thicknesses, widths, and types were presented. In three of the tested slabs, LVL with all veneers glued lengthwise was used (LVL R). In one LVL slab, a fifth of the veneers were glued crosswise (LVL X). Laminated veneer lumber slabs are engineering wood products with several important performance characteristics, making them a sustainable and preferred solution in civil engineering. To ensure the safe operation of a building with LVL structural elements, it is important to know their dynamic properties. The basic dynamic characteristics of the slabs obtained from experimental tests made it possible to validate the numerical models of the slabs. The slab models were developed in the Abaqus program using the finite element method. The elastic and shear moduli of laminated veneer lumber used in the four slabs were identified through an optimization process in which the error between the analyzed frequencies from the laboratory tests and the numerical analyses was minimized. In the case of slabs that possess the same thickness and are composed of different LVL types, the elastic modulus of LVL R in the longitudinal direction was 1.16 times higher than the elastic modulus of LVL X in the same direction. However, the elastic moduli of LVL R in tangential and radial directions were lower than the elastic moduli of LVL X in the same directions. The above was the result of the fact that the 45 mm LVL X slab had 3 out of 15 veneers glued crosswise. In the case of slabs possessing different thicknesses but the same width and type, the elastic modulus of the thicker panel was 1.13 times higher than that of the thinner panel. After validating the models, the numerical analyses yielded results consistent with the experimental results. The numerical models of the LVL slabs will be used to develop numerical models of composite floors with LVL panels in future research. Such models will allow for the analysis of floor dynamic characteristics and user-generated vibrations, which is required when verifying the serviceability limit state. Full article

Optimization of structural elements via composition of different components is a significant scientific and practical point-of-view problem aimed at obtaining more economical and environmentally friendly solutions. This paper presents the results of a static work analysis of small-size laminated veneer lumber (LVL) beams reinforced by a Carbon Fiber Reinforced Polymer (CFRP) sheet. The nominal dimensions of LVL beams were 45 × 45 × 850 mm, and 0.333- and 0.666-mm thick reinforcement layers were used. The reinforcement was applied on opposite sides of the cross section obtaining a sandwich-type structure. An epoxy resin was used as a bonding layer. The bending tests were conducted in the so-called four-point bending static scheme in edgewise and flatwise conditions. The results of experimental tests confirmed the validity of this combination of materials. The highest load-bearing capacity was obtained for configuration, where CFRP sheets with a thickness of 0.666 mm were placed on the sides of the core, parallel to the direction of loading and the veneer’s grain in the core. The increase in this case was up to a maximum of 57% compared to the core alone. The highest bending stiffness increase, 182% compared to the core alone, involves placing two layers of sheets perpendicular to the direction of loading, i.e., on the upper and lower surfaces. The presented novel sandwich structure can be competitive against traditional steel and reinforced concrete elements in civil engineering and can be utilized as beams or slabs. Full article

This study presents a testing campaign aimed at evaluating the strength and stiffness properties of laminated veneer lumber (LVL) specimens. LVL is an engineered wood product composed of thin glued wood veneers whose use in construction for structural applications has increased due to its sustainability and enhanced mechanical performance. Despite LVL’s growing popularity, there is a lack of comprehensive information regarding stress–strain responses, failure modes, and the full set of strength and stiffness properties. These are particularly essential when LVL is employed in pure timber structures or composite systems such as steel–timber or timber–concrete load-bearing elements. This research aims to bridge this knowledge gap, focusing on crossbanded LVL panels, known as LVL-C, crafted from Scandinavian spruce wood, which is an LVL product with 20% of crossbanded veneers. The study explores LVL-C mechanical behavior in three primary orthogonal directions: longitudinal, tangential, and radial. A series of mechanical tests, including compression, tension, shear, and bending, was conducted to provide a thorough assessment of the material’s performance. In compression tests, different behaviors were observed in the three directions, with the longitudinal direction exhibiting the highest stiffness and strength. Tensile tests revealed unique stress–strain responses in each direction, with gradual tension failures. Shear tests showcased varying shear stress–strain patterns and failure modes, while bending tests exhibited significant strength and stiffness values in flatwise bending parallel to the grain and flatwise bending perpendicular to the grain. This paper summarizes the comprehensive testing results and discusses the obtained strength and stiffness properties of LVL-C panels, providing valuable insights into their mechanical behavior for engineering applications. Full article

This study develops a framework for determining the material parameters of layered engineered wood in a nondestructive manner. The motivation lies in enhancing nondestructive evaluation (NDE) and quality assurance (QA) for engineered wood or mass timber, promising construction materials for sustainable and resilient civil structures. The study employs static compression tests, guided wave measurements, and a genetic algorithm (GA) to solve the inverse problem of determining the mechanical properties of a laminated veneer lumber (LVL) bar. Miniature LVL samples are subjected to compression tests to derive the elastic moduli and Poisson’s ratios. Due to the intrinsic heterogeneity, the destructive compression tests yield large coefficients of variances ranging from 2.5 to 73.2%. Dispersion relations are obtained from spatial–temporal sampling of dynamic responses of the LVL bar. The GA pinpoints optimal mechanical properties by updating orthotropic elastic constants of the LVL material, and thereby dispersion curves, in a COMSOL simulation in accordance with experimental dispersion relations. The proposed framework can support estimation accuracy with errors less than 10% for most elastic constants. Focusing on vertical flexural modes, the estimated elastic constants generally resemble reference values from compression tests. This is the first study that evaluates the feasibility of using guided waves and multi-variable optimization to gauge the mechanical traits of LVL and establishes the foundation for further advances in the study of layered engineered wood structures. Full article

In timber construction, there are still no standardized wall–ceiling system connectors made of wood for cross laminated timber construction (CLT). Based on experimental investigations of the bar-shaped dovetail connections, a wood–wood system connection was developed at the University of Innsbruck. First, the traditional dovetail connection for bar-shaped beam connections was investigated. The findings showed the high potential of force transmission in the flank area, especially for beam connections of the same height, where the height of the pre-timber is too small. To date, the load-bearing capacity of the flanks has not been taken into account in the calculation methods. To increase the force transmission paths in the base of the tenon, it was shaped in steps. This led to a load redistribution and thus delayed the failure of the connection. The knowledge gained formed the basis for an independent connecting element that resulted in the so-called “double dovetail”. The connector is a three-dimensional, statically effective double dovetail element. The wood system connector is made of block-glued laminated veneer lumber (LVL) and is manufactured in a CNC-milling process. The results of the tests showed the high performance potential of the LVL system connector, which can play an important role in future timber construction. Full article

Core–shell composites with strong weather resistance, mechanical strength and creep resistance can be prepared using co-extrusion technology. Considering the weak bonding strength between core–shell interfaces, this study started from the concept of a mortise and tenon combination; three types of conical, rectangular and trapezoidal mortise and tenon joints were prepared, and their bending properties, long-term creep properties, interfacial bonding properties, and dimensional stability properties were tested. Results showed that the mortise and tenon structure could form a mechanical interlock between the outer-shell-layer polyvinyl chloride (PVC) wood–plastic composite (WPVC) and the inner-core-layer laminated veneer lumber (LVL), which could effectively improve the interface bonding property between the two layers. Among them, the trapezoidal mortise and tenon structure had the largest interface bonding force compared with the tapered and rectangular mortise and tenon structure, where the interface bonding strength reached 1.01 MPa. Excellent interface bonding can effectively transfer and disperse stress, so the trapezoidal mortise and tenon structure had the best bending properties and creep resistance, with a bending strength of 59.54 MPa and a bending modulus of 5.56 GPa. In the long-term creep test, the deformation was also the smallest at about 0.2%, and its bending properties, creep resistance and interface bonding performance were also the best. The bending strength was 59.54 MPa and the bending modulus was 5.56 GPa; in the long-term creep test, the strain curve was the lowest, about 0.2%. In addition, the mortise and tenon structure could disperse the stress of the inner shell LVL after water absorption and expansion, thus significantly improving the dimensional stability of the co-extruded composite after water absorption. Full article

This paper presents the results of experimental testing of the bending strength and modulus of elasticity in edgewise bending of unreinforced and reinforced seven-layer LVL (laminated veneer lumber) poplar veneer panels. The aim of the research is to determine the influence of woven carbon fibers on the improvement of the bending properties and modulus of elasticity of LVL bending in the plane of the plate, as well as the influence of adhesives on the bending properties of the composite product, in order to test the potential of using this newly obtained material as a structural element. Bending was performed on small-scale samples. The main research task is the examination of three types of reinforcement, which differ from each other in position, orientation, and number of layers of reinforcement, using two different types of adhesives: epoxy adhesive and Melamine Urea Formaldehyde Resins (MUF). The composite material was produced in four different combinations in relation to the orientation and position of the reinforcement in the layup. The applied reinforcement is defined through three different configurations (EK1, EK2, and EK3) and a fourth control sample (EK4). Each configuration was produced by applying the two previously mentioned types of adhesives. The research findings showed that in the case of samples produced by applying CFRP (carbon fiber reinforced polymer) using epoxy adhesive, it significantly affected the increase in bending strength and flexural modulus of elasticity. The average improvement in bending strength is 32.9%, 33.2%, and 38.7%, i.e., the flexural modulus of elasticity is 54.1%, 50.7%, and 54.7%, respectively, for configurations EK1, EK2, and EK3, compared to control sample EK4. During the testing, the test samples from reinforced panels EK1 and EK2 showed partly plastic behavior up to the fracture point, while the diagram for the test samples from reinforced panels EK3 shows elastic behavior to a considerable extent, with a significantly smaller plastic behavior zone. This research proved the impossibility of using melamine-urea formaldehyde adhesive to form a composite product based on veneer and carbon fabric. The greatest contribution of this work is the experimentally verified and confirmed result of the possibility of applying poplar veneer to design structural elements in LVL using epoxy adhesive. Full article