EXPERIMENTAL CYCLIC TESTS ON CLT HOLD-DOWN CONNECTIONS SUBJECTED TO A COMBINATION OF SHEAR AND TENSION

Cross-Laminated Timber (CLT) structures dissipate energy during earthquake only in mechanical connections, which are located in few specific zones. The full definition of their structural behaviour and their correct design is then of crucial importance, especially in seismic conditions. Many studies were carried out on this topic during the last decade in Europe, North America and Japan in order to define monotonic and cyclic behaviour of mostly used connections when only one action (i.e. tension or shear) is prescribed. Nevertheless, some questions are still unanswered. In particular, during earthquakes, connections are subjected simultaneously to both shear and tension. The interaction between shear and tension forces may affect connector’s capacity in terms of strength, stiffness, ductility and dissipation capacity. Moreover, the possibility of brittle failure or excessive strength degradation of connections subjected to combined tension and shear action must be taken into account. This work presents the results of an extended experimental programme on CLT hold-down connectors conducted at CIRI Buildings & Construction Laboratory, University of Bologna. Cyclic tests were performed using a specifically developed test setup suitable to apply both tension and shear actions on the connections, simultaneously. In particular, the experimental tests on hold-downs were conducted prescribing a shear deformation and then loading the connection in tension according to the cyclic loading protocol prescribed by standards. The results of these tests, in terms of strength, stiffness, energy dissipation, strength degradation and ductility, are presented and critically discussed. A comparison between the experimental values of load-carrying capacity and stiffness and those obtained with calculations using existing design code provisions are given. Results obtained in this work allow to define some design guidelines and calculation rules for metal connectors in CLT structure. In addition, they provide the basic information for advanced and reliable investigation on the behaviour of CLT structure when subject to earthquake loadings.