Development of a Composite CLT of Japanese Fast-growing Trees Sendan and Cedar

Abstract

Cross-laminated timber (CLT) is attracting attention as a new wood-based material and is expected to contribute to the increased consumption of domestically produced timber, such as sugi (Cryptomeria japonica), and carbon fixation through the use of wood as a building in the city. Sugi CLT are characterized by low shear rigidity and shear strength against bending deformation in orthogonal layers. In general, hardwoods have excellent shearing properties, and when used in orthogonal layers in CLT, the shearing properties are expected to be improved. Therefore, we attempted to improve the shearing performance of CLT using a domestic fast-growing broad-leaved tree, Sendan (Melia azedarach), which has a high carbon fixation capacity. We attempted to improve the shear performance of the CLT by combining sugi and sendan. As a result of measuring the physical properties of Sendan, it was found that it has the same shear strength as beech and better shear performance than softwood such as Sugi. We prototyped a composite CLT made of Sugi and Sendan and conducted bending and horizontal shear tests. Consequently, no shear failure was observed in the composite CLT owing to the bending tests, and an improvement in performance was confirmed. Analysis of the stress distribution in the sandwich panel model showed that the shear stress distribution during bending failure was almost the same for cedar CLT and composite CLT, confirming that the shear failure performance was improved.