P 1620 - New dimensions of slip resistant joints in steel structures - The use of friction shims to significantly increase the slip resistance coefficient

To optimize connections with HSFG bolts and reduce the amount of work required, friction shims have proven to be efficient in mechanical engineering for increasing slip factors. Friction shims are washers made of different carrier substrates in which friction-enhancing particles are embedded. These particles penetrate into the surfaces of the components to be joined in order to increase the load-bearing capacity of the preloaded connection. So far, there has been no evidence regarding the transferability of this connection technology to steel structures with increased corrosion protection requirements and component-specific imperfections. In addition, the design specifications according to DIN EN 1993-1-8 and DIN EN 1993-1-9 as well as the execution specifications according to DIN EN 1090-2 were not applicable. Therefore, in this research project, slip factors and classes of friction surfaces according to DIN EN 1090-2, Annex G were determined as design parameters in DIN EN 1993-1-8 for characterized surface and friction shim configurations. For surfaces with a base coat according to ZTV-ING (GBEP-Zn), class C (𝜇 = 0,30) could be assigned for various friction shim configurations, and for galvanized surfaces with varying galvanization parameters (galvanization temperature and silicon content), even class A (𝜇 = 0,50) could be assigned. The test program according to DIN EN 1090-2, Annex G takes creep deformation of the surfaces into account, and creep behavior of the friction shims could be excluded. Since blasted surfaces can already be classified in the highest class of friction surfaces (A with 𝜇 = 0,50), connections with friction shims are currently not suitable for use despite the increase in load-bearing capacity (when the friction shim configuration is matched to the surface properties). An introduction of a higher class of friction surfaces would be conceivable. The fatigue resistance according to DIN EN 1993-1-9 was determined for various surface and friction shim configurations to assure the applicability of preloaded connections with friction shims in dynamically loaded structures. The detail categories according to DIN EN 1993-1-9 for connections with HSFG bolts and friction shims could be confirmed, and surface disruption of the friction surfaces was ruled out. Creep deformations occurring as a result of cyclic loading must be limited by restricting the maximum slip factor to the nominal value of the slip factor. In addition, large-scale tests revealed an influence of component imperfections on stress redistribution within the connection, which was further investigated using FE simulations. Further research is r of preloaded connections. Finally, based on the experimental and numerical investigations, design specifications were compiled that enable the design of connections with friction shims in accordance with DIN EN 1993-1-8 and DIN EN 1993-1-9. An execution guideline developed in consultation with friction shim manufacturers and steel construction companies ensures a secure and user-friendly execution of connections with friction shims in future application cases.