Slip-resistant connections made of carbon and stainless steel

Abstract

Slip-resistant connections are always used when slip in a connection will endanger the serviceability or the slip resistance is used for ultimate limit reasons. Hence, slip-resistant connections shall be designed to prevent slip in bolted connections. Different guidelines/standards specify slip factors for common surface conditions. For deviating surface conditions, the slip factor shall be determined experimentally. However, practice shows that in many cases the given slip factors are not comparable for the same surface condition. Furthermore, the available slip factors are valid for slip-resistant connections made of carbon steel. Currently there is no guideline or standard which prescribes a classification for slip-resistant connections made of stainless steel. Stainless steel alloys suffer more from viscoplastic deformations in comparison to carbon steel. For this reason, there have historically been a number of concerns about the use of stainless steel in preloaded bolted connections. Having more viscoplastic deformations might lead to higher losses of preload in stainless steel bolts and consequently may influence the slip-resistant behaviour of the connection. Moreover, a suitable slip factor shall be determined experimentally for each common surface condition. Currently, different test procedures for the determination of slip factors exist. However, in several cases the test procedure is not clear in detail and allows several possible interpretations. This can lead to incomparable results for identical surface preparations. Besides all these parameters, there are still many others which may influence the determination of the slip factor process. Therefore, a comprehensive investigation was conducted in the European Research Project SIROCO (RF SR-CT-2014-00024) to close the still existing gaps in knowledge in this area. In the frame of this study, the influence of different parameters on the slip-resistant behaviour of bolted connections was investigated. Furthermore, the relaxation behaviour of preloaded bolted connections made of stainless steel was also investigated. A comprehensive experimental investigation was conducted in order to provide a classification for slip-resistant connections made of stainless steel. In addition, an alternative method for preparing the faying surfaces of slip-resistant connections was developed in order to reduce the preparation time and cost on the one hand, and on the other to significantly improve the slip-resistant behaviour of the connections. A comparative study was then conducted to check the comparability of the results according to EN 1090‑2, Annex G; and RCSC, Appendix A. Finally, a simplified test specimen geometry was developed based on the EN 1090‑2, Annex G standard test specimen geometry in order to reduce the testing costs for the determination of slip factors.