Experimental investigation on in-plane stiffness and strength of innovative steel-timber hybrid floor diaphragms

An innovative steel-timber hybrid floor diaphragm with modular prefabricated composite elements is presented. Building elements have been designed to be quickly joined on site using only bolts and screws. The paper mainly deals with an experimental study on the response of the hybrid floor under horizontal loads. Monotonic and cyclic shear tests of a full-scale floor were executed in order to investigate the in-plane stiffness, bearing capacity, effective stress state and strain state, as well as damage to floor components. The forces transmitted through the timber and steel components were also assessed. The test results showed that the main deformations of the floor were localised at the beam-to-beam steel joints while the steel-timber hybrid elements behaved elastically without breakages. The use of CLT panel-to-panel connections was very effective in increasing the stiffness and the ability to recover the initial non-deformed shape after the removal of the acting loads. The findings revealed how the diaphragm behaviour of the floor was influenced by the mutual interaction between the modular staggered composite elements and in particular by the response of the connections. Several design recommendations for steel and timber connections are therefore provided here.