In timber connections, screws have a benefit over dowels or nails, as due to their withdrawal capacity they can transfer loads both perpendicular and parallel to the screw axis. Screws display their largest stiffness and load-bearing capacity in the direction parallel to the screw axis. These properties can be taken advantage of in case timber elements are connected with screws inserted under an angle with respect to the shear plane. Although a calculation method for the translational stiffness of connections with inclined screws is currently not included in Eurocode 5, multiple methods are discussed in the literature. This work focuses on the rotational stiffness of connections with inclined screws, which remains
a considerable knowledge gap to date.

An extensive literature study is carried out, in which methods for the calculation of translational stiffness of inclined screws as well as methods for the calculation of rotational stiffness of dowel-type fasteners are studied. Combinations of these methods are used to put forward fourteen calculation methods for the rotational stiffness of inclined screw connections. Rotational stiffness tests of connections with inclined screws have been carried out prior to the start of this thesis project. The calculated rotational stiffness values of each of the fourteen methods are compared to the experimentally obtained values. Two prototypes of a novel truss concept developed at Karlsruhe Institute of Technology, in which inclined screws are implemented in the chord-diagonal connections, are modelled in Rhinoceros Grasshopper. The influence of the rotational stiffness of the chord-diagonal connections on the serviceability and ultimate limit state behaviour is studied.

A correction for friction occurring between the timber members as a result of the specific sequence of the application of the loads in a subset of the rotational stiffness experiments is proposed. After this correction, the best method shows good similarity with experimental results, yielding a coefficient of determination of 0.79 for a total of 91 tests. With regard to the truss model, it is concluded that the rotational stiffness has no influence on the deflections of the truss, however, the moments in the connections increase for higher rotational stiffness values. Individual screws in the connections are found to receive an additional load of 5-10 % in their main loading direction as a result of the moments in the connections in the large-scale truss prototype. The model can be used in the preliminary design of these trusses to quantify moments in the connections and the forces per screw as a result of these moments.