Briefing: Experimental and theoretical bending stiffness of cross-laminated timber panels

Cross-laminated timber (CLT) is an engineered timber product comprising boards of strength-graded timber glued together in laminae to form large plane sections. CLT sections are used to create structural elements including walls, floors and roofs. This briefing paper presents the results of a series of stiffness tests, including both composite sections and their constituent individual component boards. The composite results are compared with the output of three widely used design calculation methods: the shear analogy method, the gamma method and the K-method. This comparison demonstrates the sensitivity of the calculated stiffness to the variation in component stiffness between recorded and graded values. As there is a lack of readily available in-depth test data linking recorded component stiffness to recorded composite stiffness, this paper aims to improve the understanding of the link between these two values. The results have shown that the gamma method was the only design calculation that remained conservative, whether using characteristic properties or true recorded stiffnesses.