Beton- und Stahlbetonbau最新文献

Formation of secondary cracks in bending members

Crack formation in bending members is generally considered by means of a representative tensile bar within the tension zone. The size of this tensile bar is defined by the effective depth of reinforcement. In this context, no distinction is made between primary and secondary cracks. This approach typically enables economical reinforcement quantities and layouts, while at the same time ensuring acceptable crack widths in real structural members. In the second generation of Eurocode 2, however, the calculated crack width for all bending members is increased by linear extrapolation over the concrete cover in accordance with the strain distribution in the cracked cross-section. The underlying assumption is that the crack width in bending members increases linearly from the crack tip at the level of the neutral axis towards the tension face. Such extrapolation may lead to a significant increase in the required reinforcement to limit crack widths. In contrast, research results indicate that crack geometry varies with cross-sectional depth and type, and that crack patterns with pronounced secondary cracks, in particular, do not exhibit a linear increase in crack width towards the tension face. This contribution therefore addresses the question of whether the general extrapolation of the calculated crack width to the tension face is universally valid—and if not, under which boundary conditions this extrapolation should be restricted.

Analysis of the applicability of the concrete cone capacity design method in recycled aggregate concrete

The usage of recycled aggregate concrete and low-emission cements for structural concrete production, and as a result as an anchoring material for post-installed fasteners, raises challenges for the design method for post-installed fasteners as specified in EN 1992-4 due to partially altered material behaviour. The current application limits specify normal concretes C12/15–C90/105, while the associated assessment documents assume the use of natural aggregates, and cement types CEM I or CEM II/A or CEM II/B. Existing research on the use of post-installed fasteners in recycled concrete has indicated the requirement for further investigation. This publication presents an analysis of the application of the design model (concrete cone capacity design, CCD-method) and the default k-value for the failure mode concrete cone failure as proposed in EN 1992-4, based on experimental investigations performed at the Institute of Structural Engineering – BOKU University and additional test data available in the literature. The results show that, with increasing percentage of recycled aggregate, an adaptation of the pre-factor seems to be necessary in order to ensure the applicability of the design model.

Zum Titelbild: Kreislaufwirtschaft im Bauwesen – das beinhaltet nicht nur das Recycling von Betonbruch, sondern unter anderem auch die Wiederverwendung von Bauteilen. Damit dies funktionieren kann, braucht es wissenschaftlich fundierte Methoden und ingenieurtechnische Konzepte. Geforscht wird dazu unter anderem an der Ruhr-Universität Bochum. Dort wurde 2022 ein Forschungsgebäude zurückgebaut und im Zuge dessen einzelne Bauteile entnommen, an denen umfangreiche Untersuchungen durchgeführt werden. Das Herausheben einer Platte für die spätere Wiederverwendung ist auf dem Titelbild zu sehen. In dieser Ausgabe werden einige mögliche Ansätze zu modularem Bauen und automatisierter Fertigung vorgestellt. (Foto: Jannik Hoppe)