Originally developed in Europe, self-tapping screws (STS) have become the proprietary fastener of choice in recently built mass timber buildings in North America. STS offers some advantages over other types of fasteners, such as (a) installation of STS inside wood members is easier as it does not require pre-drilling of holes inside members, (b) the yield moment, torsional strength and tensile strength of STS is comparatively high as the material forming the screw is usually hardened after rolling the thread, (c) the stiffness of the resulting connection is higher and the chances of slipping are less (Frese and Blass, 2009), and (d) STS with long threaded lengths makes it feasible for use in large structural members, e.g., mass timber products.
Recently, issues have been raised on failures of STS due to shrinkage and swelling of wood products resulting from moisture content changes, particularly during construction in the coastal climates. Failures of STS have been reported by structural engineers and contractors of several mass timber projects in NA. This has greatly increased the liability of practitioners involved in mass timber construction.
This project will investigate the material properties of several types of mass timber products and self-tapping screws. These material properties will be used in an analytical and numerical prediction model to describe the behaviour of self-tapping screws in mass timber products under moisture content variation.