P 869 - Laser-welded T-joints - Development of the fundamentals and optimisation of production for use in shipbuilding and steel bridge construction

P 834 - Investigation of bolted connections in steel and composite construction for the creation of rules for the numerical design of structural fire protection in building construction In this research project, connections in steel and composite construction with high-strength bolts of strength class 10.9 are investigated in the event of fire. With the introduction of the component method, it is now possible to simulate entire structures at room temperature, taking into account the connection behaviour. This is not yet possible in the case of fire, as on the one hand there is no implementation of the component method or a comparable numerical model for the case of fire and on the other hand there are no validated material laws available for high-strength bolts in the case of fire. For this reason, material parameters for high-strength bolts of strength class 10.9 during and after a fire are initially developed on the basis of test series. This includes both the investigation of the pure bolt material by means of stationary and transient hot tensile tests and the investigation of bolt assemblies in tensile and shear tests. In the latter, not only the material but also the bolt geometry has a major influence on the behaviour. The tests show that the screws fail in the temperature range up to 420°C due to the usual thread stripping. In the temperature range from 420°C to 650°C, however, the screws fail due to a crack in the thread base. It can be shown that this crack is due to liquid metal induced stress corrosion cracking (LME). Above 650°C, the screws fail due to flank bending. As a result of the material investigations, validated material parameters will be available in future for modelling bolts within connection simulations, which take into account the various forms of failure at different temperatures. In addition, thermal and mechanical numerical models will be developed to describe the behaviour of head plate and flag plate connections in steel and composite construction. The models are validated by fire tests on two standard structural connections. Within the tests and the numerical models, a temperature field is taken into account, which is based on the unit temperature-time curve and a typical fire protection coating with an intumescent coating. A head plate connection in steel construction and a flag plate connection in composite construction are analysed. In the case of the flag plate connection, it is assumed that it is a hinged connection at room temperature. It is shown that a moment resistance can occur in the event of fire, provided that the premature failure of the continuous reinforcement is prevented. Finally, simplified spring models are developed for the two connection types on the basis of the component method, which can be used to determine the stiffness and load-bearing capacity of the connections in the event of fire. In summary, it will be possible in future to describe the behaviour of connections in the event of fire on the basis of validated bolt properties using finite element or spring models and to take this into account in structural calculations. The IGF project 16586 N of the Forschungsvereinigung Stahlanwendung e.V., Düsseldorf, was funded via the AiF within the framework of the programme for the promotion of joint industrial research (IGF) by the Federal Ministry for Economic Affairs and Energy on the basis of a resolution of the German Bundestag. The project was carried out at the Gottfried Wilhelm Leibniz University of Hanover by the Institute of Steel Construction and at the Technical University of Darmstadt by the Institute of Steel Construction and Mechanics of Materials. Publication: July 2014