Strength Prediction of Mass-Timber Panel Concrete-Composite Connection with Inclined Screws and a Gap

Mass timber panels (MTPs) are a new generation of engineered wood panels that are available in large plane dimensions to facilitate fast floor construction with the obvious environmental benefit of being from a renewable material. In floor construction, concrete slab or topping is often applied over the MTPs to improve various performance attributes, including structural, acoustic, and vibration serviceability. A mass timber panel-concrete (MTPC) composite floor system often consists of a MTP connected to the concrete layer with mechanical fasteners and a sound insulation layer in between. The capacity of this type of composite system mostly depends on the strength of the connection, and often tests are performed to characterize connection properties required for structural design. In lieu of testing, analytical models can be developed to calculate connection properties based on component properties. To that end, two analytical models were developed for solid and layered timber by characterizing all possible kinematical failure modes for directly predicting the strength of a connection with inclined screws and an insulation layer. According to Johansen’s yield theory, the strength of a laterally loaded connection is controlled by the dowel-bearing effect of the fastener in timber, but joints with an inclined screw have a more complex behavior because of the combined bearing and withdrawal action of the screw. In the developed models, both the dowel-bearing and withdrawal action of the screw are considered along with the bending capacity of the screw and friction between the members. Both models were experimentally validated with a wide range of material properties. It was found that the models are capable of predicting the mode of failure of a connection and the load-carrying capacity within 10% of the experimental value.