Ultra high strength fillet- and butt-welded joints made of S960: Load-carrying capacity and deformation behaviour

High and ultra-high strength steel can contribute to more sustainable structures by saving construction weight and resources. In FprEN 1993-1-8 modified design rules for butt- und fillet-welded connections have been implemented for steels up to S700 that consider the special characteristics of welded high-strength steels. prEN 1993-1-12 will be valid for steels up to S960 and consequently, the design concepts have to be extended up to S960. For this purpose, in the research project “Effective design concepts for mixed connections in steel structures” an extensive experimental program of ultra-high strength welded connections was tested. For butt welds, 36 specimens with steel grades S960MC or S960QL and different filler metals G46 and G89 were used. Furthermore, the plate thickness and weld joint geometry were varying parameters. The fillet welds were made of S960QL, t = 20 mm with varying filler metals G46, G69, G89 and T89, resulting in a total of 12 experimental tests. Tensile tests with optical strain and optical extensometer measuring were conducted to examine the load-carrying capacity and deformation behaviour of the welded test specimens. Moreover, further material investigations were carried out, such as microhardness mappings on in cross-sectioned welds and tensile tests of the weld metal. With the results obtained from the research project, proposals for extensions of the design concepts for butt- and fillet-welded connections up to S960 were developed that can be incorporated in prEN 1993-1-12. The investigations carried out and the formulation of design recommendations enable a wide use of ultra-high strength steels. This allows material savings and future-oriented, sustainable constructions.