Jan Reinheimer, M.Sc.

A large number of steel structures in Germany are constructed using high-strength bolted joints. In addition to the higher load-bearing capacity of these fasteners, the application of a pre-tensioning force also ensures a higher cyclic load-bearing capacity and safety against automatic loosening. The current design standard DIN EN 1090-2, Eurocode 3 and DASt guideline 024 specify the level of preload force, the installation method and the inspection of the installation for high-strength bolt sets.

The latter includes checking for overtightening, whereby a precise definition of this is only given for the combined tightening method and the applied angle of rotation. If this is exceeded by a general value compared to the normative specification, the applied preload force is considered to be too high. This can result in the entire bolt assembly having to be replaced.

There is a lack of scientific knowledge about the utilisation of the bolt set defined as overstressed and the influence on the material and the load-bearing behaviour. The planned research project therefore aims to develop the technical and scientific basis for the use of overelastically prestressed, high-strength bolt sets.

The consequences and damage caused by an overelastic preload force are to be characterised and classified so that the load-bearing behaviour can be evaluated. The aim of the research is also to identify a limit value for unplanned over-elastic pre-tensioning in order to avoid the replacement of bolt sets and, if necessary, to enable them to be reused.