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Klimaschutz und Klimawandel
(2022)
Composite dowels have opened new possibilities for engineers designing composite structures. The fundamental and most important characteristic of composite dowels is the shape of the cutting line. It is important to understand why only one particular shape of the cutting line is used in bridge engineering, while so many different shapes have been investigated by many researchers. The essential part of the process of developing composite dowels – the development of the shape of the cutting line – is presented in this paper. The influence of the steel web thickness is presented, and technological problems of steel fabrication are highlighted. The role of empirical experience from the first bridges, push-out tests, and finite element simulations is presented. Assumptions for numerical procedures are given. The distinction between the steel failure and concrete failure modes is introduced for composite dowels. The paper presents how the concept of “shape” was divided into “shape,” “ratio,” and finally “size,” and how, because of the fatigue problems in bridges, all the three factors have emerged to result in the form of shapes that can satisfy the requirements for bridges. Research leading to the invention of the first version of the clothoidal shape is presented.
Starting from Germany, the VFT® bridge girder technology (prefabricated composite beam) has spread in several European countries in the last decades as further development of the standard steel-concrete composite solution. Its configuration fits perfectly to integral frame bridges built over existing infrastructure with the scope to minimize the traffic disturbance. In this paper a further development with the focus on cost efficiency in span ranges of 40-55 m is proposed: the VFT-RS technology. The change consists in using standard rolled sections by adapting them into the integral frame bridge configuration, further enhancing the structural efficiency with the benefits of high- steel strength. The constructive details to achieve the polygonal form have been studied to allow easy fabrication and a maximal clearance height over highway traffic lanes. The VFT-RS solution is conceived as the economic option of standard highway overpasses, with the aim of an overall construction cost reduction of 5%.
At the University of Applied Sciences Potsdam, students are introduced to working with built structures in the field of practical building analysis in the master's degree in civil engineering. The basis for the existing analysis is the geometry, materials used and the structure. New structural calculations are required for modifications or extensions. The students are taught which non-destructive testing methods can be used to determine the material properties of the building fabric. In addition, it is presented how the teaching is structured and using examples that show that teaching can be designed to be very practice-relevant.
This paper introduces (both formally and technically) a new concept: a hybrid steel–concrete cross section. The definition is based on the shear force transmission mechanism and it assumes the existence of a new type of shear connections, i.e. composite dowels. The hybrid cross-section is a generalization of composite steel-and-reinforced concrete cross sections and it is defined by a new way of dimensioning for vertical shear. The hybrid cross section concept is based on a specific approach to the lever arm of internal forces and an assumption that the local shear transfer mechanism of composite dowels is different than in the case of classic welded studs. The concept makes it possible to show by design calculations that the shear force is transferred through jointly the concrete part and the steel part. It is worth emphasizing that the proposed concept is a response to the new opportunities provided to engineers by composite dowels and to the fact that the bridge structures designed nowadays are different from the ones designed previously. The concept enables the design of completely new types of composite steel–concrete beams. The presented theoretical analyses verified by means of FEM show how the change of the shear connection level influences the division of the shear force in the cross section. This is included in the design concept through the internal lever arm of the hybrid section. The proposed concept has been shown to be internally consistent and complete.
Vor der industriellen Produktion von Stahlträgern und Brettschichtholz boten Zahnbalken eine Möglichkeit große Auflagerabstände im Hoch- und Brückenbau zu überspannen. Verzahnte Balken sind aus heutiger Sicht als nachgiebig zusammengesetzte Biegeträger zu betrachten. Dabei wirken die handwerklich hergestellten Zahnverbindungen in gleicher Weise wie zum Beispiel Dübel besonderer Bauart. Der zur statischen Nachweisführung benötigte Verschiebungsmodul ist in der aktuell gültigen Holzbau-Bemessungsnorm DIN EN 1995–1–1:2010 nicht ausgewiesen. Somit ist es zurzeit nur durch eine versuchstechnische Ermittlung des Verschiebungsmoduls für die jeweilige Zahngeometrie möglich, statische Nachweise durchzuführen.