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Investigations of the limit preload force of high‐strength bolt and nut assemblies In DIN EN 1090‐2, the decisive specifications, for preloaded bolts a subsequent control of the assembly is specified. Among others, preloaded bolts have to be checked for overtightening. If a bolt is classified as overtightened, this can result in the entire bolt group having to be replaced. In addition to the high cost of replacement, this often means that further work has to be temporarily halted. However, there is a lack of knowledge about the degree of utilization of the bolt defined as overtightened. In order to assess the bolts with regard to overtightening, DIN EN 1090‐2 gives a maximum exceeding of the specified angle of further rotation for the combined method. Experimental investigations on bolts of diameters M16 and M20 with different lengths showed that overelastic preloading forces only have a significant influence on the load‐bearing behavior from the onset of necking. The evaluation of prestressed bolts with regard to overtightening, as specified in DIN EN 1090‐2, seems to be too general and too conservative for the bolt diameters and lengths investigated so far. [ABSTRACT FROM AUTHOR]

Extended keynote paper of Eurosteel 2021 Automated production is finding its way into the fabrication of structural steel. One robot holds attachments (stiffeners, end plates, etc.) on a steel beam or column and another robot produces weld seams. However, welding robots can also be used for Additive Manufacturing (Wire and Arc Additive Manufacturing, WAAM). The wire electrode serves as a printing material. The Institute of Steel Construction and Materials Mechanics in Darmstadt is investigating how typical connecting elements for steel structures can be printed directly on steel beams using Additive Manufacturing with arc welding and robots. Furthermore, structural elements such as nodes for space frames can be printed and even complete structures, e.g. columns and a little bridge, have already been manufactured additively. The main focus is on determining suitable welding and process parameters. In addition, topology optimization is necessary in order to achieve good structures using a small amount of material. This is possible due to the free design prospects of WAAM, which opens up new design and production strategies. [ABSTRACT FROM AUTHOR]

Examination of the interaction of bending and compression at the support of sandwich panels The interaction of bending moment and the compression at the support of sandwich panels is assessed experimentally. DIN EN 14509 [1] gives a 3‐point‐bending‐test in which the span depends indirectly on the thickness of the panel. The span is the decisive factor since it gives the ratio of moment to compressive force. Therefore, it was analysed how long the span shall be to represent real systems well. The parameter‐study led to the conclusion that the span might be between 1 m and 12 m for realistic results. DIN EN 14509 [1] usually asks for 4 m to 6 m. Tests were performed to improve the understanding of the relevant mechanisms [2–5]. The over‐ resp. under‐estimation of the span leads to deviations in the serviceability criterion of up to ± 20 % (wall) and ± 30 % (roof). Finally, a recommendation is given to consider these deviations in practical design. [ABSTRACT FROM AUTHOR]

Load bearing behaviour and design of bolts under combined tension and shear The load bearing behaviour of bolts that are exposed to a combined tension and shear load were fundamentally assessed in a research project at the Institute of Steel Construction and Materials Mechanics at the Technical University of Darmstadt. Trigger for this approach was, that the evaluation of the existing test results on the topic for the evolution of the Eurocode 3 Standards had shown, that the hitherto established quadratic interaction rule for the design of combined loaded bolts is not on the safe side. This finding led to a change in the design rule in Eurocode 3. A more detailed investigation of the existing data shows that the number of the hitherto conducted tests on the subject is surprisingly small, while the results are of limited suitability for an evaluation due to missing base values such as accurate material properties. A fundamental investigation on how combined loaded bolts behave is completely missing. Thus, the existing studies were newly evaluated in summary, new test series were conducted, these were reproduced using Finite Element modelling and therewith the behaviour was fundamentally observed and analysed. Using parameter studies, the transferability of the results was ensured. In the text in hand the findings are summarized and the possibilities of a future handling of the design of bolts are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Tightness of sandwich constructions – Water and air tightness in longitudinal joints and window connection joints. The air and water tightness of the envelope play an important role in the planning of modern buildings due to the ever increasing requirements in terms of energy conservation. For sandwich structures, which contain many joints due to the prefabricated elements, the design of these joints is of particular interest. In addition to the normative specifications regarding the joint tightness of sandwich panels, this report also explains the associated laboratory test procedures. Subsequently, the results of experimental and numerical investigations of various research projects are presented and conclusions for the production and assembly of sandwich elements are shown. All in all, it can be stated that very tight building envelopes can be realized with sandwich panels while observing important basic rules in production and assembly. [ABSTRACT FROM AUTHOR]

Diaphragm effect of sandwich panels. Full scale tests were carried out within the scope of [5] to investigate the diaphragm action of sandwich panels. Shear diaphragms were constructed to assess the load carrying action of the sandwich panels bracing the structure. The bearing behaviour of the various components contributing to the shear diaphragm effect was investigated in more detail on smaller experimental set ups. These small scale tests include investigations into the screw connections between the sandwich panels and the substructure, as well as a series of tests on the load transfer through the longitudinal joint between the individual panels. The most untapped potential for improvement of the bearing capacity has been found to be the influence of the longitudinal joint. An increased force transmission in the longitudinal joint leads to higher values of stiffness and maximum bearable load of the shear diaphragm. Various methods to improve the contribution of the joints were developed. Of these, the hook-and-loop tape joint reinforcement has been found to yield the best results. Therefore, this reinforcing method has also been investigated in full scale tests. The use of hook-and-loop tape in the longitudinal joint makes the panels acting as one big plate. The impact on the screw connection has been successfully reduced by improving the load transfer in the longitudinal joints. [ABSTRACT FROM AUTHOR]

Active learning for civil engineers - examples for the use of digital media at a university. The digitalization of teaching (at university) has been a much discussed topic for several years. There are many different approaches that also have a different impact on the daily work at the university. Additionally, an increasing emphasis on competence orientation of the degree programs is being demanded politically. At the chair for steel structures at TU Darmstadt, digital media are being used for several years and in different settings. The following article presents some variants. The basis of all these teaching concepts is the idea to activate more students during class. Thereby a better learning performance should be reached. [ABSTRACT FROM AUTHOR]

Die mittlerweile baurechtlich eingeführte DIN EN 1090-2, die die Ausführung von Stahltragwerken regelt, gibt für Schnittflächen von Stahlblechen einen zulässigen höchsten Härtewert an. Solche Grenzwerte waren in den zuvor geltenden deutschen Normen nur aus der Schweißverfahrensprüfung bekannt. Da die gemessene Härte den neuen Grenzwert bei Schnittkanten, die mit den gängigen Schnittverfahren hergestellt wurden, oft überschreitet, stellt die neue Regelung die produzierenden Firmen vor große Probleme. Insbesondere bei planmäßig nicht weiterbearbeiteten Schnittkanten stellt sich die Frage, inwieweit die Aufhärtungen die Oberflächenvorbereitung für den Korrosionsschutz beeinträchtigen und sich negativ auf die Haftzugfestigkeit der Beschichtung auswirken. Um herauszufinden, welche Zusammenhänge hier bestehen, wurden an verschiedenen Brennschnittkanten Versuche zur Bestimmung der Härte und der Rauigkeit durchgeführt und der Einfluss der Kantenhärte auf die Haltbarkeit von Beschichtungen untersucht. The influence of the hardness of heat cut edges. The meanwhile introduced DIN EN 1090-2, which settles the execution of steel structures, gives a maximum permissible hardness value for cut edges of steel plates. In German standards comparable limit values where thitherto only known in conjunction with the welding procedure qualification. Due to the fact that the measured hardness on edges, which were cut with the established cutting methods, often exceeds this new maximum value, producing firms are faced with problems. Especially for edges that do not get milled the question arises, what influence the increase of hardness has on the surface preparation for anticorrosive coating and whether it has any effect on the adhesive tensile strength of the coating. To find out which correlations exist here, tests were conducted on different thermal cut edges. Hardness and roughness were measured and the influence of these values on the resistance of the coating was tested. [ABSTRACT FROM AUTHOR]