Experimental and numerical investigations on timber-concrete connections with inclined screws

In new and existing buildings, it is important that floors are sufficiently strong and stiff in plane. In comparison with pure timber floor systems, timber-concrete composite structures are often used as floor solutions to better combine acoustic separation with both greater load-carrying capacity and increased stiffness, also resulting in significant improvement of the serviceability vibrational comfort. The choice of a structurally effective yet inexpensive shear connection between the concrete topping and the timber joist is crucial to make the composite floor a viable solution that can compete with reinforced concrete and steel floors. The use of inclined screws to connect the timber beam to the concrete topping represents a possible solution to maximize the slip modulus of the connection and, at the same time, to keep the construction cost within acceptable values. In this paper, the mechanical behavior of such a type of timber to concrete connection is explored via experimental pushout tests and numerical investigations. The specimens tested were made of an inner timber block connected to two outer concrete slabs by means of two 8 mm diameter screws per side. To reproduce the timber flooring used in real practice as permanent formwork for the placement of the concrete topping, an OSB layer was introduced between the timber block and the concrete slabs of the specimens. Experimental results were statistically assessed to compute the mean slip moduli and the characteristic values of the shear strength. A mathematical model of an inclined elastic beam on an elastic foundation capable to provide the slip modulus of the system was developed. The dependency of the slip modulus upon the screw inclination and the interlayer flooring thickness was also investigated. The accuracy of the theoretical results was assessed through comparisons with experimental results.