Connections with inclined screws and increased shear plane friction

Joist to header connectors are widely available in different shapes and sizes. One of the most common types resembles dovetail connections, where two parts slide into each other to enable load transfer (Figure 1a). Usually, aluminium is used for the connectors. One scope of the here presented project was to replace the aluminium with densified veneer wood (DVW). The connectors are mostly fastened with self-tapping and fully threaded screws, which are often inclined by 45° to the connector plane. In such connections with inclined screws, the load parallel to the shear plane is mainly transferred by axial screw loading, see Bejtka & Blass (2002). Due to equilib-rium conditions, a compressive force results perpendicular to the shear plane. This compressive force leads to frictional resistance, which depends on the size of the compressive force and the coefficient of friction µ. For connections with inclined screws, this additional load-carrying capacity can be taken into account by default, although the screws are loaded in tension. This is the difference to connections un-der combined lateral and tensile load, where the load increase due to friction, i.e. ... mehrthe rope effect, cannot be applied. Another scope of the project was to utilize the frictional resistance, which depends on the size of the compressive force and the co-efficient of friction (COF). Therefore, two possibilities can be examined: (i) increasing the compressive force by designing the connection to reach the tensile capacity of the screws and (ii) increasing the COF by treating the surface adequately. The latter was done in this study.