Erhöhung der Tragfähigkeit von GV‐Verbindungen durch den Einsatz von Klebstoff

Use of adhesives to increase the load‐bearing capacity of slip‐resistant connections. Slip‐resistant connections are preferred for steel constructions if subjected to fatigue loads and/or load reversals, no slip in the connection is permitted and joining on construction site is necessary. These connections are prepared with a high manufacturing effort due to the intensive preparation of the faying surfaces, or the contact area between the steel plies and it must receive special consideration in design and coating application. The typical corrosion protection for steel structures is still the hot‐dip galvanizing. The follow‐up work of the faying surfaces for a use in slip‐resistant connections is related to a high effort and guarantees no high slip factors. Furthermore the slip factor may deviate more or less high with the properties of the zinc layer. Against this background, investigations have been carried out in a recently concluded research project which show an increase in the load bearing capacity of slip‐resistant connections by the combined use of adhesive. In the case of the process combination, which is also referred and named as a preloaded hybrid connection, the applied preload of the high‐strength bolts is responsible for the considerable increase in load bearing capacity compared to the elementary joining processes – adhesive bonding or just slip‐resistant connections. If the two methods are carefully combined, the individual load bearing capacities can approximately add up.     

Tragfähigkeit von randnahen Kopfbolzen bei der Versagensart seitlicher Betonausbruch

Kopfbolzen, die sehr nahe am Bauteilrand verankert werden, können infolge seitlichen Betonausbruchs versagen. Bei dieser Versagensart kommt es zu einem Abplatzen des Betons auf der Seitenfläche des Bauteils. Die Berechnung der Tragfähigkeit erfolgt dabei mit dem CC‐Verfahren. Numerische und experimentelle Untersuchungen zeigen, dass der bisherige Berechnungsansatz konservative Ergebnisse liefert. Um den Einfluss einzelner Parameter auf die Tragfähigkeit zu bestimmen, wurden Versuche verschiedener Autoren ausgewertet und ergänzende numerische Untersuchungen durchgeführt. Diese zeigen, dass – der kritische Randabstand von 3.c₁ auf 2.c₁ reduziert werden kann. – der Einfluss des Randabstandes geringer als bisher angenommen ist. – der Einfluss der Betondruckfestigkeit unterschätzt wird. – der Einfluss direkt nebeneinander liegender Kopfbolzen nicht berücksichtigt wird. Um wirtschaftlichere Ergebnisse für die Tragfähigkeit von randnahen Kopfbolzen zu erhalten wird ein modifizierter Berechnungsansatz aufgezeigt, der die Versuchsergebnisse und numerischen Berechnungen gut abbildet. Dieser Ansatz findet Eingang in die neue europäische Bemessungsnorm 'Design of Fasteners for Use in Concrete' und ermöglicht damit eine genauere Berechnung von Kopfbolzenverankerungen nahe am Bauteilrand für die Versagensart Blow Out. Load Bearing Capacity of Headed Studs in Case of Blow Out Failure Mode Headed studs placed near to the edge of a concrete member can fail because of blow out. In case of this failure mode the concrete spalls at the lateral surface of the concrete member. The failure load can be calculated by the Concrete capacity method (CCmethod). Numerical and experimental investigation show that the CC‐method leads to conservative results. To determine the influence parameters on the load bearing capacity the tests of different authors are evaluated and advanced numerical simulations are carried out. The evaluation shows that – the critical edge can be reduced to two times the edge distance. – the influence of the edge distance is smaller than assumed. – the influence of the concrete compressive strength is underestimated. – the influence of headed stud placed sided by side is not considered. To get more economic results relating the load capacity of headed studs at the edge a modification of the CC‐Method is proposed. This modified CC‐method corresponds quite well with the test results as well as with the results of the numerical simulations. The proposed design equation will be included in the European design guide 'Design of Fasteners for Use in Concrete'.     

Höherfrequente Hämmerverfahren – Ursachen der Steigerung der Ermüdungsfestigkeit und Nachweismodell

Der Einsatz von Schweißnahtnachbehandlungsverfahren zur Optimierung wechselnd beanspruchter Stahlkonstruktionen in Hinblick auf deren Lebensdauerverlängerung oder eine Reduzierung des Konstruktionsgewichts wurde in den letzten Jahren verstärkt untersucht. Dabei erwiesen sich höherfrequente Hämmermethoden als besonders wirkungsvoll zur Steigerung der Ermüdungsfestigkeit. Der vorliegende Artikel zeigt die Potentiale der Verfahren auf und belegt deren Einfluss auf das Rissinitiierungs‐ und Rissfortschrittsverhalten von Schweißnähten. Anhand eines entwickelten Bemessungsmodells wird eine Möglichkeit der rechnerischen Erfassung der positiven Wirksamkeit der Verfahren dargelegt. Reasons and calculation of the improved fatigue life of welds treated with high frequency peening methods. The application of post weld treatment methods in order to optimize fatigue loaded steel structures in view of an extension of their service life or a reduction of the construction weight has been studied intensively in the last years. High frequency peening methods proved to be extreme effectively in order to increase the fatigue strength. The following article shows the potentials of the methods and proves their influence on the crack initiation and crack propagation behaviour of welds. With help of a developed design procedure the possibility of respecting the positive effect on the fatigue strength during the design is provided.     

Numerische Analyse geschweißter Verbindungen von Duplexstahl und Quarzglas

Numerical analysis of welded joints between duplex steel and quartz glass. Welded joints are a vital element in structural engineering. Originating from conventional carbon steel welding in construction, recent advancements in welding technology now allow the joint of modern high‐strength steel and glass materials. With today's methods, an analysis of the welded joints' structural behaviour can be conducted by experiment, as well as by numerical analysis. Particularly for the numeric analysis, capturing the non‐linear thermal and mechanical properties of the materials is important, in order to allow a realistic determination of temperature, microstructure and residual stresses for different types of joints. Simulations of multi‐layered weld joint on duplex steel show, that a targeted heat treatment during MAG‐welding by variation of the welding parameters achieves a beneficial ratio between ferrite and austenite which, for example, ensures a high resistance of the weld to corrosion. The material quartz glass can generally be welded as butt‐weld with a CO₂‐laser. The simulations of a welded joint of a plate and a pipe show, that an optimization of the welding technology of preheat laser beam and welding laser beam is necessary, in order to reduce the thermal impact during the welding process, as well as residual stress in the joint. At the Department of Steel Structures at the Bauhaus‐Universität Weimar, numerical simulations of welded joints between steel and glass materials are a current and topical research focus.