Withdrawal Properties of Self Tapping Screws

The withdrawal capacity Fw is especially important for joints with self-tapping screws, because these joints are, above all other joints with dowel-type fasteners, perfectly suited to transmit high forces in axial direction of the fastener. Consequently, a considerable amount of publications is available dealing with withdrawal behaviour of screws, with publications by Ringhofer (2017), Brandner et al. (2018; 2019), Brandner (2019) and Westermayr and van de Kuilen (2020) being the most recent. All studies contain large testing series that vary parameters such as timber products, screw types or insertion angles. Usually, the final aim is to derive empirical design equations, where Westermayr and van de Kuilen relate the withdrawal capacity of screws inserted parallel to the grain with the longitudinal shear strength. A particular study was carried out in Hölz (2021), who investigated the influence of pitch and thread angle on the withdrawal behaviour with the aim to develop an optimised thread geometry.