Cross laminated timber (CLT) diaphragms under shear: Test configuration, properties and design

The orthogonal structure of cross laminated timber (CLT) diaphragms under shear can cause three possible shear failure mechanisms: (i) gross-shear (in case of narrow-face bonded laminations), (ii) net-shear and (iii) torsion. While the resistance against torsion has been investigated comprehensively, the determination of in-plane gross- and net-shear strength remains a challenging task. Whereas gross-shear properties are proposed in analogy to glulam, for net-shear only properties derived from testing single CLT nodes are available. The verification of these approaches for full CLT elements has yet to be confirmed. We aim on verifying the applicability of a corresponding novel test configuration. For this aim and for evaluation of net- and gross-shear strength and modulus, an experimental study comprising in total 23 series featuring different parameter settings was conducted. In doing so, the operational efficiency of the test configuration together with reliable shear failure of all tested CLT elements was observed. With regard to the conducted parameter study, results qualitatively correspond with tests on single CLT nodes. Gap execution and layer thickness are confirmed to be the main parameters significantly influencing in-plane shear properties. Based on gathered experiences, characteristic shear properties and a conclusive design concept are proposed.