Tightening behaviour of preloaded stainless steel bolting assemblies

Preloaded bolting assemblies made of stainless steel are currently not permitted in steel structures due to the unknown viscoplastic deformation behaviour as well as the unknown tightening behaviour and tightening procedures for these kinds of bolting assemblies. Nonetheless, the construction industry wishes to carry out these types of connections in special cases, e.g. when special requirements exist with regard to corrosion resistance or for architectural reasons. Generally, the tightening behaviour of carbon steel HR and HV bolting assemblies according to EN 14399-3 and -4 cannot simply be transferred uncritically to stainless steel bolting assemblies due to several reasons. Within the scope of the European RFCS research project SIROCO, extensive investigations are currently being conducted on the tightening and preloading behaviour of EN ISO 4014 and EN ISO 4017 bolting assemblies made of austenitic and duplex stainless steels. First results from this project show that a targeted tightening of such assemblies is in principle possible. Specified preloading levels, e. g. Fp, C* and Fp, C, can be achieved with sufficient reliability using suitable lubricants. Herewith, it is possible to define feasible tightening procedures. Furthermore, it could be shown that these bolting assemblies show sufficient ductility and galling of the assemblies can be for sure avoided. The present paper provides an initial insight into the results of the project.