The compressive strength in the major direction of cross-laminated timber CLT is the key to supporting the building load when CLT is used as load-bearing walls in high-rise wood structures. This study mainly aims to present a model for predicting the average compressive strength of CLT and promoting the utilization of CLT made out of planted larch. The densities and compressive strengths of lamina specimens and CLT samples with widths of 89 and 178 mm were evaluated, and their relationship was analyzed to build a prediction model by using Monte Carlo simulation. The results reveal that the average density of the lamina and CLT were about equal, whereas the average compressive strength of the CLT was just about 72% of that of the lamina. Width exerted no significant effect on the average compressive strength of the CLT, but homogenization caused the wider CLT to have a smaller variation than that of the lamina. The average compressive strength of the lamina could be calculated by using the average density of lamina multiply by 103.10, and the average compressive strength of the CLT could be calculated according to the compression strength of lamina in major and minor direction, therefore, a new prediction model is determined to predict the average compression strength of CLT by using the average density of lamina or CLT, the average compression strength of CLT made in this study is about 74.23 times of the average density of the lamina. The results presented in this study can be used to predict the average compressive strength of CLT by using the average density of lamina and provide a fundamental basis for supporting the utilization of CLT as load-bearing walls.
Cross-laminated timber (CLT) is a wood panel product that can be arranged in different ways. The advantage of utilizing CLT is the ability to use lamination even with low density materials or those that have defects, like knots. This study evaluated the bonding and bending performances of CLT utilizing domestic species in a shear wall or floor via a face bonding test of layers and a three-point bending test. The tests were carried out with three-layered CLT made up of Japanese larch and/or Korean red pine in various configurations. The layer arrangement for lamination was divided according to the species and grade of the wood. The out-of-plane and in-plane bending tests were conducted on the CLT according to the applicable direction in a wooden structure. The results of the bonding test showed that the block shear strength and delamination of all types of CLT met the BS EN 16351 (2015) standard requirements. The results of the bending test based on two wood species showed that the bending strength of the larch CLT was higher than that of the pine CLT in single species combinations. For mixed species combinations, the bending properties of CLT using larch as the major layer was higher than those using pine as the major layer. This demonstrated that the major layer had more influence on the bending properties of CLT and that Korean red pine was more suited for the minor layer of CLT.
To develop a high-performance, lightweight cross-laminated timber (CLT) floor, this study tested the delamination performance between carbon fiber-reinforced plastic (CFRP) and CLT and the bending performance of a CFRP composite CLT that was differently reinforced according to the shape of CFRP. The test results showed that the soaking and boiling delamination between CLT and CFRP of the CFRP composite CLT produced by spreading a polyurethane (PUR) adhesive at 300g/m2 were both less than 5%, satisfying the Korean standard. Furthermore, the composite CLT (3ply) of which the entire outer surface of the tension laminae was reinforced with a CFRP plate (thickness: 1.2 mm) showed a mean MOE and a mean MOR higher by 27% and 48%, respectively, than those of the unreinforced CLT (3ply). Furthermore, even though the weight of this CFRP composite CLT was smaller than that of 5ply CLT by approximately 40%, its bending moment was measured higher by 14% than that of the 5ply CLT (thickness: 175 mm) fabricated by limited state design (LSD) as specified in PRG-320.
In this study, cyclic tests were performed on the larch CLT shear walls depending on the half lap reinforcement of half-lap connections and reinforced plywood of spline connections in order to evaluate the horizontal shear performance of the larch CLT walls. The test results show that there is no difference in residual strength depending on the reinforcement of half-lap connection, but their initial stiffness has been increased by 9%. There was no significant difference either in the residual strength of double spline connections depending on the application of reinforced plywood, while the spline reinforcement has failed to increase initial stiffness. All of the larch CLT walls constructed according to the edge connection shape were measured to have a strength reduction ratio of less than 10% in each horizontal displacement intervals and an equivalent viscous damping ratio of less than 10% for energy dissipation in the initial and final horizontal displacement intervals, thereby confirming that their excellent horizontal shear performance and seismic performance.
As timber tends to be weak against the load perpendicular to grains, it can be important to study the consequences of applying loads perpendicular to larch cross-laminated timber (CLT) composed of multiple larch laminae. Compression tests were conducted perpendicular to the in-plane and out-of-plane grains of Japanese larch CLT. Out-of-plane average compressive strength, average yield strength, and average compressive stiffness perpendicular to the grain of the larch CLT were 11.94 N/mm2, 7.30 N/mm2, and 7.30 N/mm3, respectively, whereas the in-plane average compressive strength, average yield strength, and average compressive stiffness perpendicular to the grain of the larch CLT were 21.48 N/mm2, 21.18 N/mm2, and 18.72 N/mm3, respectively. The in-plane compressive strength and yield strength showed a statistically significant relationship with the density of CLT, the modulus of elasticity measured by longitudinal vibration (MOELV), and the average MOELV of the laminae constructing the cross-laminated timber. The in-plane yield strength was affected by the MOELV of the outer laminae and the average MOELV of the larch cross-laminated timber. The compressive strength properties were most affected by the loading surface of the CLT. The variation between the moisture content and compressive strength properties of the CLT, however, was not statistically significant.
The strength performance of edge connections between the cross-laminated timber (CLT) panels, as currently applied to CLT construction, was compared to that of connections reinforced with glass fiber-reinforced plastic (GFRP) by means of a tensile-type shearing test. In this study, the reinforced half-lapped connection is intended to prevent CLT from coming apart due to failure of self-tapping screws (STS) by bonding GFRP sheets to connections between CLT panels. The end-distance and edge-distance of this reinforced half-lapped connection were designed to equal 5D (where D is the fastener diameter) and 4D, respectively, which is shorter than the 6D recommended by European Technical Approval (ETA). Nevertheless, the yield strength was increased by 7%, and the stiffness by 92%, compared to the non-reinforced half-lapped connection. In addition, the internal spline connections using GFRP-reinforced plywood were 57 and 36% higher than the connection made up of LVB or plywood, respectively, and the energy dissipation percentages were 400 and 76%, respectively. These results indicate that the reinforcement effect of the connection by the GFRP was very significant. On the other hand, the half-lapped connection of the larch CLT improved the strength performance as the end-distance increased, and the end-distance had a greater effect on the strength performance than the edge-distance.
Bamboo-like glulam beams with hollow section units and intermittent internal reinforcement pieces were produced with small-diameter larch-wood pieces and one-component polyurethane. To better understand the design reliability, the failure mode, ultimate bearing capacity, and application potential were evaluated. Three types of beams (solid glulam, hollow glulam, and bamboo-like rectangular glulam beams) were compared and analyzed in this work. Stiffener pieces glued inside the bamboo-like beam were found to increase the bearing capacity and improve the failure mode relative to the hollow glulam beam. Comparison of the hollow section with a similar outside diameter showed that the ultimate bearing capacity increased by approximately 12.3% when the spacing between the stiffeners was 270 mm, and the ultimate bearing capacity increased by approximately 18.0% when the spacing between the stiffeners was 135 mm. Compared with the solid timber beams, wood consumption was reduced by 26.4% and 25.7% for the hollow and bamboo-like glulam beams, respectively. Also, a parameter analysis of the reasonable spacing and thickness of the stiffener was proposed by the finite element method.
Cross-laminated timber (CLT) is becoming increasingly adopted into wooden construction of South Korea. Due to the lack of standards and protocol for CLT, there are many problems in the production and utilization phases. This study focused on the deformation and defects of CLT due to humidity variations. In this study, small, cross-laminated specimens were manufactured using three layers of laminated larch planks that had various moisture contents. The dimensional changes of these specimens were measured in response to changing internal conditions including side adhesion or moisture content variation and external conditions such as humidity. Shrinkage in width and thickness was less than 1.0% when using dry planks as the cross-laminated specimen. However, high-moisture content (MC) planks were not suitable when used as the surface layer of the CLT, as the shrinkage in width and thickness were greater than 2.0%. When high-MC planks are used in the inner layer, their shrinkage must be less than 2% to prevent splitting caused by a MC difference between the surface and inner planks. For this purpose, laminates with a MC less than 15% should be used for CLT.
Hollow glilam beam has some advantages that the traditional solid glulam beam does not have, such as the convenience for wiring construction and comparably light weight. Four-point bending tests of three solid glulam beams and 15 hollow glulam beams with various sizes of rectangular holes produced from small-diameter larch timber were conducted to investigate the influence of the hollow ratio and wall thickness on bending stiffness and load capacity. The midspan deflection, cross-section strain, and ultimate load were obtained from the tests, and the detailed failure models and apparent MOE for all specimens are reported. Hollow glulam beams with the hollow ratio ranged from 25% to 40%, and the wall thickness greater than 20m after the assumption of plane section under bending moment. The apparent bending stiffness and ductility of hollow glulam beam were less than those of solid glulamb beam, and the apparent MOE is 0.86 times the elastic modulus value calculated by theory of elasticity. In addition, a calculation formula for the ultimate bending moment is proposed.
The bending strength of hybrid wooden-core laminated timber (HWLT), a composite material made from existing cross-laminated timber (CLT) and plywood, was analyzed. Using plywood makes it possible to decrease the bending strength of the starting material. Korea Larch (Larix kaempferi Carr.) was used as plywood because of its popularity in Korea. To analyze HWLT’s bending properties, each component (lamina, plywood) was tested for bending, compression, and tensile strengths. The results showed that the HWLT’s bending strength depended on the plywood’s number of plies. With an increased number of plies, plywood’s bending strength decreased, and also HWLT’s bending strength decreased. Most of the failure showed in-plate shear failure of plywood. This result meant that use of reinforced plywood made it possible to increase HWLT’s bending strength for structural material.