P 1203 - Design of crane structures made of laser beam and laser hybrid welded ultra-high and ultra-high strength steels under consideration of the metallurgical notch

P 1205 - Characterisation of the load-bearing behaviour of resistance spot welded joints of ultra-high-strength steels under cyclic loading and development of a calculation concept for fatigue strength Driven by CO2 legislation and the growing demands on vehicle safety, functionality and comfort, a key approach in lightweight car body construction is to reduce the overall vehicle mass. Innovative lightweight body construction concepts with steel variants such as ultra-high-strength dual-phase and complex-phase steels are therefore required, which enable effective weight savings thanks to their outstanding strength combined with good forming properties. As knowledge of resistance spot welding of these steels, particularly in the area of fatigue strength, is only available to a limited extent, the results obtained as part of the project will help to ensure that this joining technology continues to be used successfully. Fatigue strength values are particularly useful for small and medium-sized companies, as they do not have the necessary knowledge and capacities. In order to cover a wide range of applications and for reasons of comparability and to supplement previous findings, investigations were carried out using the LWF-KS-2 test concept under cyclic loading. Fatigue strength values of spot-welded joints of these steels, determined with the aid of the LWF-KS-2 test concept, are not yet available and form the basis for the project. Experimental investigations generally entail a large financial outlay due to the required scope and duration of the tests, which is why analytical calculation methods for the design processes were developed as part of the project and corresponding design information was provided. In order to realise an efficient and practical design of spot-welded connections by analytical means, the existing set of rules, the "Rechnerische Festigkeitsnachweis für Maschinenbauteile", or FKM guideline for short, was used and expanded. A corresponding transfer function enabled the user to successively calculate the component fatigue strength for the specific application using characteristic values of the connection (e.g. quasi-static characteristic values) that could be determined at low cost or suitable literature values. In addition to the actual research objective, the crack initiation location was also analysed and the further crack progression investigated. The failure behaviour from crack initiation to complete failure of the spot-welded joints could be determined with the cut-off according to characteristic changes in stiffness or frequency and taken into account in the design based on the FKM guideline. Through simple engineering assumptions and the estimation of factors, it was possible to compare and verify analytical calculation results with the experimentally determined results for the analysed spot-welded joints. Especially in the areas of construction and design of spot-welded joints, the characteristic values determined are available to the user and extend the applicability of the FKM guideline. Against this background, the investigations carried out enable the efficient and economical development of spot-welded components made of ultra-high-strength dual-phase and complex-phase steels. Publication: 2019 Authors: Prof. Dr.-Ing. G. Meschut

P 1200 - Innovations for optimising the use of weathering-resistant structural steel in steel and composite bridge construction Compared to unalloyed structural steel, weathering-resistant structural steel is characterised by significantly higher corrosion resistance. As a result of natural corrosion processes, a firmly adhering, dense coating forms on the surface of the unprotected weathering-resistant structural steel, which slows down further corrosion. Due to the slowed corrosion reaction of the weather-resistant structural steel, use under natural corrosion conditions is also possible and permissible without an additional corrosion protection system. As many steel and composite bridges in Germany show signs of damage due to age and design, there is a great need for durable and low-maintenance replacement structures. Due to its naturally occurring, maintenance-free corrosion protection, corrosion-resistant structural steel can fulfil this requirement as a construction material in bridge building. Despite slightly higher material costs and necessary wall thickness surcharges, weathering-resistant structural steel offers an economical and sustainable alternative. The economic advantages of weathering-resistant structural steel over unalloyed structural steel lie in the elimination of the costs and all follow-up costs for the initial coating and standard, repeated renewal of a conventional organic corrosion protection system, as well as the associated lower environmental impact. The formation of the compact, firmly adhering top layer, which is responsible for the significantly slower corrosion behaviour of weather-resistant structural steel, is influenced by sulphur dioxide during the natural corrosion reaction. As a result of industrial structural change, the concentration of sulphur dioxide in today's atmosphere in Germany is very low, which has changed the formation of a corrosion-inhibiting oxidic surface layer under natural atmospheric weathering. The investigations showed that in the changed low sulphur dioxide atmosphere, compact and inconspicuous oxide layers still form on weather-resistant steel, which do not require any changes to the construction with weather-resistant structural steel. The visual detection of rarely occurring fatigue cracks, which is necessary in the context of bridge inspections, is difficult or even impossible for weather-resistant structural steel due to the dense and firmly adhering oxide top layer, as the corrosion-inhibiting top layer should not be removed from the component surface due to its anti-corrosion properties. This research project therefore developed a method for the geometry-independent, non-contact detection of cracks for bridges made of weatherproof steel and verified it on real bridge structures. The investigations have shown that this method is suitable for practical use and can be successfully applied to steel structures without a coating, such as uncoated weather-resistant structural steel, but also to a superficial surface layer. Cracks and scratches can be recognised on flat surfaces from a depth of 0.3 mm. Publication date: January 2021 Authors: Prof. Dr.-Ing. D. Ungermann, P. Hatke M.Sc., Prof. Dr.-Ing. habil. F. Walther, Dr.-Ing. M. Knyazeva, Dr.-Ing. S. Friedrich, Dipl.-Ing. (FH), SFI P. Lebelt

P 1208 - Consistent design model for production-optimised composite dowel bars - Basis for DASt guideline and transfer to Eurocode 4 This report summarises the investigations carried out on the load-bearing and deformation behaviour of composite dowel bars in the field of structural engineering. The competitiveness of this economical and also technically sensible composite material is limited in comparison to conventional shear stud dowels by the fact that only a national and time-limited approval is currently available. In contrast, shear connectors are firmly anchored in European regulations. In order to contribute to the integration of bonded dowel bars into the European standards, the participating research institutions focussed on the investigation of bonded dowel bars in cracked and non-cracked concrete, under longitudinal shear, tensile and combined shear-tensile loading as well as in installation positions close to the surface. New failure mechanisms were observed and recorded using appropriate design formulae. First, existing studies on composite dowel bars, as well as existing research results and design models, were reviewed and summarised. Subsequently, experimental and numerical investigations were carried out on the load-bearing capacity of bonded dowels in non-cracked concrete. The results of the small-part tests were used to derive approaches for the load-bearing behaviour under shear, tensile and combined shear-tensile loading. Component tests with three different test arrangements were used to verify the models, thus covering a wide range of possible constellations of bonded anchors under combined loading in building construction. The load-bearing capacity of the composite anchors in the beam always turned out to be better than predicted on the basis of the small-part tests. The design models therefore provide a reliable estimate of the real load-bearing capacities. Based on this, test specimens with bonded dowels were produced and tested in transversely and longitudinally cracked concrete. It was shown that longitudinal cracks have no load-reducing effect on the shear load-bearing capacity of bonded dowel bars and therefore do not need to be taken into account in the design for predominantly static loads. In contrast, a decrease in the shear load-bearing capacity was observed for transverse cracks in the concrete. Furthermore, the load-bearing behaviour of bonded dowels in installation positions close to the surface was investigated. This led to the failure case of edge breakage, which has not yet been taken into account in the current type approval and was observed in small part and beam tests. Statistically verified design equations were derived on the basis of these findings. The existing model of the shear load-bearing capacity was extended on the basis of the new findings, while the failure mode of shearing of the concrete dowel was reviewed and categorised as not relevant for the calculation. Publication: January 2021 Authors: Prof. Dr.-Ing. M. Feldmann, K. Wolters, M.Sc., Prof. Dr.-Ing. W. Kurz, Y. Broschart, M.Sc., Prof. Dr.-Ing. Hegger, Dr.-Ing. M. Claßen, G. Christou, M.Sc.

P 1209 - Wheel load induced fatigue of crane runway girders for heavy metallurgical cranes With the replacement of DIN 18800 and DIN 4132 and the introduction of the Eurocodes for steel construction regulated by building law, it has become apparent that the fatigue analyses for highly stressed crane runway girders, such as those found in steelworks, have undergone significant changes. Compared to the previous design, stricter notch classifications, particularly in the area of wheel load application, must be taken into account. These changes can go as far as doubling the thickness of the cross-sectional components, which would mean, for example, that web plates of up to 80 mm would also have to be taken into account, whose K-seam connections to the flange would be associated with considerable problems in terms of production and monitoring and would also no longer be justifiable from an economic point of view. Against this background, the present research project derived fatigue strengths for the crane runway-specific fatigue detail "top flange-web plate connection" in EC3-1-9 Table 8.10, in particular for the heavy metallurgical crane systems concerned, and prepared them as recommendations for a rule amendment or supplement. The focus here is specifically on the detail of the wheel load introduction with KN weld design, for which no differentiation is currently made with regard to the design quality or the manufacturing process. The essential core of the methodological approach is that existing crane runway girders from practice are recorded, documented and evaluated with regard to wheel load-induced fatigue ("best practice" experience). This allows a direct quantitative statement to be made about the fatigue safety of the detail to be analysed. In addition, numerical comparative calculations are carried out to derive synthetic notch cases and existing results from previous research work are included, although these alone were not sufficient. Finally, a concept for the successful and timely implementation of the results in current standardisation is presented. FOSTA - Research Association for Steel Application e. V. Publication: April 2019 Institute for Steel Construction, RWTH Aachen University Prof. Dr.-Ing. Markus Feldmann Sandro Citarelli M.Sc.