Stainless steels are becoming more and more popular as a construction material in both building and civil engineering structures, because of their high material strength, ductility and corrosion resistance. In this frame, the execution of slip-resistant connections made of stainless steel is necessary, e. g. in footbridges, facades etc. As no design regulations exist in any code, special experimental testing has to be performed in each case. Stainless steel alloys are thought to suffer more than carbon steels from time dependent viscoplastic deformation at room temperature. It could lead to higher preload losses and consequently to lower slip factors than achieved for carbon steels with comparable surface treatment. However, no evidence of this behaviour can be found in literature for preloaded bolted connections. For this reason, slip factors for the various stainless steel grades have to be determined experimentally if they want to be used in the steel structures. In the frame of the European RFCS-research project SIROCO, the preloading behaviour of stainless steel bolted connections as well as the slip-resistant behaviour of slip-resistant connections made of austenitic, various duplex and ferritic stainless steels have been investigated. In this paper, the results of slip factor tests on four stainless steel grades are presented and the influence of different surface treatments and the preload level on the slip factor of stainless steel slip-resistant connections is discussed. Finally, slip factors for various stainless steel grades with different surface treatments are proposed for a future implementation in the next revision of EN 1090-2.

The use of stainless steel components can lead to a significant reduction of maintenance costs compared to a structure executed in carbon steel. Because of its high material strength, ductility and corrosion resistance stainless steels are becoming more and more popular as a construction material in both building and civil engineering structures. Consequently slip-resistant bolted connections made of stainless steel are becoming more important. Slip-resistant bolted connections are used in joints where slip is not acceptable (because they are subject to reversal of shear load or any other reason) or in joints that are subject to cyclic shear load (to improve the fatigue class of the connecting plates). Existing design codes/standards do not specify slip factors for surface treatments of stainless steel grades, the minimum values of slip factors for common surface treatments/coatings that are specified in EN 1090-2 are exclusively valid for carbon steels. One of the reasons for this is that stainless steel alloys are thought to suffer more than carbon steels from time dependent behaviour (creep and relaxation) at room temperature. This could lead to higher preload losses and consequently to lower slip factors than used for carbon steels with comparable surface treatment. However, no evidence of this can be found in literature. Creep and relaxation are stress dependant phenomena and the stresses in the components of preloaded bolted connections are locally highly non-uniform. Therefore, slip factors of different stainless steel grades have to be determined by experiments to investigate the effects of time dependant material behaviour. In this paper the results of slip factor tests on four stainless steel grades are presented and the influence of surface treatments and the preload level on the slip factor of stainless steel slip-resistant connections is discussed.