Preloaded bolted connections made of stainless steel under fatigue loading in civil engineering structures

• Applicant: Professorin Dr.-Ing. Natalie Stranghöner
• Subject Area: Structural Engineering, Building Informatics and Construction Operation
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 521501197

In the construction industry, structures and bolted connections made of stainless steel are increasingly being used as load-bearing components in steel construction, e.g. in bridge structures, roadway crossings and coastal protection systems, due to their excellent corrosion resistance in aggressive environments. While in the past mainly austenitic stainless steel was used, in recent years austenitic-ferritic stainless (duplex) steel has also been increasingly used. However, preloaded bolted connections made of stainless steel in fatigue-loaded structures have so far not been considered feasible due to ignorance of the expected preload losses as a result of the viscoplastic deformation behaviour of the components as well as fears regarding cold welding effects. For these reasons, the project does not only focus on the fatigue loading capacity, but also considers the principle tightening behaviour of the boltin assemblies including tightening parameters in order to prevent premature failure of the bolts. As further aspects, the viscoplastic deformation behaviour, the interfacial pressure of the clamping package to avoid plastic deformations and thus ultimately too high preload losses are considered. The central research objective of this application is thus the development of concepts for describing and recording the load- and structure-dependent non-linear behaviour of preloaded bolted connections made of metal construction bolting assemblies made of austenitic stainless and duplex steel in the typical diameter range M12 to M36 under fatigue loading for use in the construction industry. Ultimately, the aim is to transfer these findings into boundary conditions for an optimised bolting assembly type made of stainless steel for use in the construction industry. To achieve the research objectives, an extensive programme of experiments on the aspects mentioned is planned, which will be extended by numerical FE parameter studies with FE models validated on the experiments. Finally, an analytical model for describing the viscoplastic deformation behaviour is to be developed, interfacial pressures for clamping packages made of stainless austenitic and duplex steel for use in the construction industry are to be derived, the tightening behaviour of prestressed bolted joints as a basis for developing suitable criteria for describing the requirements for minimum ductility, The fatigue strength of stainless steel bolts under tensile and shear loads will be determined and boundary conditions for an optimised type of bolting assemblies for preloading for use in civil engineering will be developed on the basis of the results obtained.

• DFG Programme: Research Grants