Cyclic tests on beam-to-column joint with steel link for timber seismic resistant structures

For the design of dissipative heavy timber frame structures, brittle timber failure modes should be avoided. To this purpose modern timber connection technology can be integrated into hybrid timber-steel system, entrusting the dissipation function to ad hoc conceived dissipation devices, like steel links, as an alternative to connections. With reference to Moment Resisting Frames (MRF), steel links can be located at the ends of the beams, for providing dissipative capacity, by means of cycles of deformations in plastic field. To this purpose, timber members and steel connections should be designed with adequate over-strength to remain in elastic field. In this perspective, the paper investigates the mechanical characterisation of two different timber beam-to-column joints with steel links for heavy timber frames, both consisting of a timber beam connected to a steel link by means of an end-plate and glued-in steel bars. This type of joint has some interesting properties in terms of mechanical performance, versatility and prefabrication. The proposed design criteria of the joints are validated through an experimental campaign carried out at the University of Minho in Portugal. In all it consists of 2 monotonic and 2 cyclic tests for each specimen up to collapse. In this work the results of the cyclic tests are presented and compared with those of monotonic tests. The tests results indicate a satisfactory agreement with the theoretical ones. In particular, the reliable prediction of the joints collapse modes allows to design moment resistant beam-to-column joints with steel link, which can undergo high plastic deformation without brittle failures, with a remarkable level of global ductility and energy dissipation under cyclic loading.