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) netshear
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 grossshear
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.