A Contribution to Friction in Timber Connections

Timber connections with inclined screws are state-of-the-art and widely used. Due to their inclination regarding the shear plane, inclined screws are practically only loaded in tension. The load-carrying capacity of connections with inclined screws can be increased because of friction in the shear plane. This work investigates surface modifications to increase the friction between connecting parts. Friction tests with the manufactured surfaces and softwood showed increased friction coefficients compared to untreated surfaces. Tests with connections with modified surfaces in the shear plane showed increased load-carrying capacities and stiffness values. An analytical model predicts the load-carrying capacity well for different surfaces and friction coefficients, screw lengths, and numbers. Overall, this work provides insights into the short-term and long-term behaviour of connections with inclined screws and increased friction in the shear plane.