Hybrid adhesively bonded timber-concrete-composite floors

Timber-concrete-composites (TCC) floors are composed of timber beams or plates connected to a concrete layer by means of a shear connector. Usually, the two materials are connected with mechanical fasteners where some degree of relative slip under load occurs. Alternatively, using adhesives to bond the concrete layer to the timber, an almost perfectly rigid connection can be created. The combination of these two jointing techniques is referred to as hybrid. In the research presented in this paper, hybrid TCC floors were investigated combining self-tapping screws with an adhesive layer. The goal was to provide sufficient adhesive bonding to satisfy the serviceability limit state (SLS) requirements, and to provide a redundant screw connection to satisfy the ultimate limit state (ULS) requirements. As a result, less adhesive is required than if designing for the ULS, and fewer screws are required than if designing for SLS; while at the same time obtaining predictable failu re modes. In total, 36 small-scale specimen tests and four full-scale floor bending tests were conducted. Two of the full-scale hybrid TCC floor segments were tested after having been exposed to serviceability loads for approximately 2.5 years. The long-term loading did not cause significant structural degradation, effective bending stiffness decreased by less than 5%.