P 1502 - Ultra-high strength structural steels in fire - Material behaviour for simplified and advanced calculation models

P 1507 - Efficient verification concepts for mixed joints in steel construction Higher-strength steels allow high stresses, particularly in the tensile range, and enable a reduction in the load-bearing cross-sections, thus leading to a reduction in material consumption and manufacturing costs. Overall, an improvement in the ecological balance is therefore achieved, not only because of the excellent material efficiency of the steel itself, but also because of the reduction in the amount of material required for the substructures. Mixed welded joints between normal-strength and high-strength steels play a decisive role here. The advantage of a dissimilar joint is that the load-bearing capacity in the area of increased stress is not adjusted by changing the cross-section, but by selecting a higher-strength steel grade. This means that large thickness jumps in the area of the seams can be avoided and a reduction in sheet thickness, seam volume and an improved ecological balance can be achieved. This research project has investigated the load-bearing capacity and deformation behaviour of butt-welded mixed joints of various steels S355 to S960 as well as high-strength and ultra-high-strength butt-welded joints made of S460, S700 and S960 in extensive experimental and numerical investigations. Fillet welded joints made of S960 were also tested. Weld filler metals, sheet thicknesses, weld preparations and energy input during welding were varied in order to analyse their influence on the welded joints. The results obtained were used to develop proposals for the extension of design concepts for prEN 1993-1-12, as well as recommendations for the design of welded joints. The objectives of the research project were achieved. Publication: January 2025 Authors: U. Kuhlmann, M. von Arnim, J. P. Bergmann, J. Hildebrand, St. Eichler, W. Flügge, A. Gericke, O. Brätz