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3DWelding – additive fabrication of structural steel elements This paper investigates the possibilities of robotic 3D printing with steel (WAAM – Wire and Arc Additive Manufacturing) in the construction industry. The aim of the project team is to develop a stable and economical manufacturing process for customized steel elements. Thus, the influence of different process parameters such as wire feed rate and travel speed on the weld shape and build‐up rate as well as on the material properties will be explained and a parameter window with stable, verified parameter sets will be defined for each material used. Three different filler metals (G 2Si1, G 3Si1, G 4Si1) are tested in terms of their strength and stiffness, with particular attention paid to the joining area between substrate and welded structure. For this purpose, test methods for testing additively manufactured components, especially for shear capacity, have been newly developed. As a proof of concept, an exemplary application is shown and the load‐bearing capacity of this connection is investigated in different configurations. [ABSTRACT FROM AUTHOR]

Unexpected fatigue cracks at main girders of a railway bridge – strain measurements under service and analyses based on fracture mechanics At a steel railway bridge, erected and taken into service in 1960, fatigue cracks were detected at some transverse stiffener to web connections at the lower flange of the main girder. These findings were surprising, because this specific connection detail was suggested in previous national design standards for fatigue. The paper presents the comprehensive strain measurements under service to show the local stress field at the critical detail within the web plate of the main girder, indicating the well‐known phenomenon of distortion‐induced fatigue, but with unexpectedly high resonance‐like bending stresses in the web. Based on fracture mechanics analyses, with implementation of the measured strain/stress data due to local and global effects at the transverse stiffener connection, as well as the measured material properties (fracture toughness and crack growth parameters) the remaining fatigue life was analysed. The positive results allow an unrestricted train operation in the future. It also turned out, that the mixed‐mode effects must be taken into account and considering only mode I at the crack tip may lead to unsafe results. [ABSTRACT FROM AUTHOR]

Universal high‐performance columns made of high‐strength steels without welding In recent years, steel‐concrete composite columns made of normal‐strength steels are seldom used owing to the economic and technological advantages of precast reinforced concrete columns. Though, the use of high‐strength structural steels bears high potential for the efficient production of composite columns with excellent structural performance that are economically competitive to precast concrete columns, there are currently major obstacles to use of the ultra‐high‐strength steels (UHSS) in Germany. Hollow section composite columns with embedded high strength steel core without welded connections provide an opportunity to regain lost market share. A research project, funded by the AiF (Arbeitsgemeinschaft industrieller Forschungsvereinigungen), is intended to explore the potential of UHSS composite columns by experimental and theoretical investigations. The present paper demonstrates the concept of such composite columns with UHSS and gives first exciting insights into the research results. In addition to column tests under ambient and fire conditions, small scale tests are necessary to investigate various influencing factors and to create the basis for new and easy to use design and construction principles that allow efficient application. [ABSTRACT FROM AUTHOR]

Mechanical material behaviour of ultra‐high‐strength structural steel S960QL in case of fire Due to their good strength‐to‐weight ratio, high‐ and ultra‐high‐strength structural steels are increasingly used in multi‐storey and industrial buildings in the form of plate material, pipes and sections. For structures with fire protection requirements, however, the use of high‐strength structural steels is currently inhibited by a lack of knowledge regarding temperature‐ and rate‐dependent material behaviour. Comprehensive knowledge of the material behaviour is a basis for a realistic modeling of the load‐bearing behaviour of steel structures. Within the framework of the FOSTA‐research project P 1502, systematic investigations of the structural material behaviour of ultra‐high‐strength steels are carried out in terms of an extensive tensile test program. The aim of the project is to characterise the mechanical material behaviour during all phases of a fire, including the cooling phase of natural fire scenarios. The paper addresses the material behaviour of quenched and tempered steel S960QL in fire. Steady state and transient state tensile test results are presented and used for the characterisation of the material behaviour during the heating phase of a fire and the comparison to common material models. In addition, the results of natural fire tests for the evaluation of the material behaviour in the cooling phase and the residual behaviour are presented. [ABSTRACT FROM AUTHOR]