P 514 - Investigation into climate protection using stainless steel

P 512 - Assessment of the fatigue behaviour of crane structures when using high-strength and ultra-high-strength steels The performance of cranes and crane construction is significantly increased by the use of high-strength steels. The standards and regulations currently in force assume that high-strength steels up to a yield strength of 460 N/mm² are to be classified in the same way as normal-strength steels in terms of their fatigue behaviour. There are no standardised regulations on the fatigue behaviour of high-strength fine-grained structural steels with yield strengths in the range of 460 to 1100 N/mm². This considerably limits the utilisation of the high strength of these steels. Therefore, the input variables for the fatigue analysis must be scrutinised more closely. As part of this research project, typical notch details for crane construction made of high-strength and ultra-high-strength steels were analysed theoretically and experimentally. Furthermore, the concept of geometric stresses, which has already been successfully applied to hollow section nodes, was applied to crane-specific notch details. In addition, measurements were carried out on selected existing crane systems in order to realistically record the actual load situation. In advance, the details for which the most urgent need for research was identified were agreed with the "Crane-specific notch details" working group. The following design details with variations in geometry and materials were analysed: - Angled connections (K-joints) - Welded-on longitudinal ribs - Laser- and plasma-cut recesses - Butt joints of sheets of different thicknesses - Welded-on lamellas or reinforcement plates The results of these investigations are used to achieve a higher utilisation of the high-strength and ultra-high-strength materials by adapting the fatigue analyses. The savings in construction weight, the reduced sheet thickness and the associated lower welding volume lead to an improvement in economic efficiency and an increase in the performance of crane and conveyor systems and their substructures. The notch catalogue of the new European standardisation can be expanded to include crane-specific notch details. Furthermore, beyond the area of hollow section nodes, a general method for determining the fatigue load with stress concentration factors and using the finite element method is specified, which is used when it is not possible to clearly assign a detail to a specific notch detail. Authors: R. Puthli ,S. Herion Steine, J. Bergers, G. Sedlacek , C. Müller, J. Stötzel, S. Höhler, Ö. Bucak Publication: 2006

P 516 - Lightweight steel and composite steel structures for building refurbishment As part of the present research project P516, the field of building refurbishment and its influencing factors were first analysed. Based on the knowledge gained, a needs analysis and assessment was carried out in accordance with a utility value analysis. The aim was to develop new construction elements from existing building products. Based on this, the following three component groups were analysed: - kinematic supporting structures - Lightweight ceiling system made of single bars - lightweight beams with webs made of sandwich elements While the first two fields were investigated exclusively on a theoretical-numerical basis, the focus in the development of a lightweight girder was on the extensive test programme carried out. The analysis of the kinematic load-bearing structures showed that the application possibilities for such a system are very limited due to the relatively high compliance. The system only achieves an acceptable level of deflection under load when a large number of locking rods are inserted, which means that the amount of work involved would be too great and economic use - even as a niche product - would be out of the question. In the "lightweight ceiling system" sub-project, initial considerations were made regarding the the required manual transport and the resulting reasonable loads. Based on the knowledge gained, the focus of the sub-project was initially on the investigation of suitable cross-sections in addition to the fundamental analysis of the load-bearing behaviour. An extensive parameter study was carried out. The main difficulty was the search for a suitable connection method, whereby connections based on wedging were ultimately favoured. The system is well suited for use in structural maintenance and renovation. When developing a lightweight beam using sandwich elements, small-scale tests were initially carried out to identify suitable fasteners, accompanied by analyses of the materials used. In addition to self-tapping screws, adhesive joints proved to be suitable for connecting the beam web (sandwich element) to the flanges (folded sheet metal). More than 40 component tests were then carried out, whereby numerous parameters were varied. These included the type of load application, the beam height, the thickness and beading of the surface layers, the geometry of the chords and the combination of several fasteners. In addition, the behaviour of the girder without chords was analysed as well as the behaviour of girders with large web cut-outs for the building equipment. Using a new test technique, it was possible to apply a linear load to the beam by utilising hydrostatic pressure. The newly developed beam showed a very high load-bearing capacity with a low dead weight and at the same time a benign failure. In the load-bearing state, a combined state was achieved in addition to the bending load-bearing effect due to the formation of a tension band. A combination of adhesive and screw connections proved to be ideal with regard to the fasteners used. A numerical study carried out in parallel using the FE method revealed the optimisation potential of the beam. The design proposal presented is based on a deflection limitation of the beam. In conclusion, it can be stated that with the lightweight floor system and the beams with webs made of sandwich elements, two different options were developed that are well suited for use in the renovation of structures. Authors: U. Peil, D. C. Ruff Publication: 2006

P 511 - Further development of clinching technology for joining organically coated steel sheets The aim of the research project was to optimise and further develop clinching technology for joining coil-coated semi-finished products in order to largely limit or avoid the paint damage that occurs with the current state of clinching technology. With regard to reducing coating damage, both the surfaces and geometries of the clinching tools and the coating systems were optimised. The aim was to achieve a significant improvement in visual appearance and corrosion resistance. As part of the project, various liquid and powder coating systems used, for example, in the household appliance industry and in steel furniture construction were investigated. These coating systems were applied to a standardised substrate on a laboratory scale in order to exclude the influence of the substrate material. The tests were carried out using a clinching system with a three-part mould from BTM and a clinching system with an unsplit mould from TOX. The degree of coating damage after the clinching process was primarily assessed visually. Furthermore, the LWF developed a top-mounted measuring cell that allows very good comparative measurements to be made on the clinched joints with regard to the degree of coating damage. However, precise statements about the extent of the damaged coating area as a function of the of the measured current flow, due to the sensitivity of the measurement method with regard to time, temperature, etc., is currently not possible. The results indicate that, with regard to the chemical basis of the analysed liquid coating systems, the polyester coatings showed better clinching suitability than the polyurethane systems. In principle, it can also be said that the pre-treatment of all coating systems has a decisive influence on the adhesion of the coating to the substrate and that there is great potential for optimisation here. Significant improvements in clinchability were achieved by optimising the coatings and pre-treatments. The use of clinching tools optimised in terms of geometry and surface also made it possible to reduce coating damage on both the punch and die sides without reducing the joint strength, in some cases even considerably depending on the coating system. The extensive investigations carried out as part of the project showed that the coating damage is generally highly dependent on the coating system to be clinched. By using clinching tools with optimised geometry and surface, damage to the coating layer could be reduced, but not completely prevented. Authors: O. Hahn, L. Schmidt, B.A. Behrens, S. Hübner, F.W. Bach, M. Schäper Publication: 2010