Axially Loaded Self-Tapping Screws in Solid Timber and Laminated Timber Products

Within the last 25 years, self-tapping screws have become the most relevant fasteners in contemporary timber engineering. Restricting the scope to their axial loading, the present thesis aims on gaining a fundamental knowledge concerning the specifics of this kind of dowel-type fastener. The related considerations are divided into the two main topics, namely the (steel) product “self-tapping screw” itself and the withdrawal behaviour, defined as the axial composite interaction with the timber material where it is inserted into. With regard to the product performance, the main outcomes are the derivation and verification of a mechanical approach, describing the relationships of its relevant design properties in dependence of a geometrically varying thread profile, as well as some fundamental findings in terms of fatigue-relevant loading and hydrogen-induced stress corrosion cracking (HISCC). In case of the withdrawal behaviour, based on about 14,000 experimental results, the impact of several influencing parameters is determined, discussed and described by means of empirical, stochastic and mechanical modelling. Parameters, where a significant influence was found, are finally included in the determination of a universal approach for the prediction of the screw’s mean and characteristic withdrawal strength, irrespective the timber product used and the position the screw is inserted into.