Slip modulus of inclined screws in timber–concrete floors

This paper presents a model for the stiffness of inclined screws used as shear connectors in timber and concrete composite floors. Screws inclined in the direction of slip have been shown to provide a higher stiffness (slip modulus) than vertically placed screws. An increased slip modulus per screw enhances the effective flexural stiffness of a partially composite timber and concrete beam, or, alternatively, allows the same flexural stiffness to be achieved with fewer screws. The model assumes that the screw behaves as a beam on a two-dimensional elastic foundation: it takes account of the inclination of the screw and models the timber as orthogonal springs with differing stiffnesses in the grain and transverse directions. The model also considers axial deformation, and hence shear lag, of the screw. Optimum inclination angle and embedment length of screw can be predicted. Preliminary validation of the model is provided by comparison with some experimental results.