Beton- und Stahlbetonbau最新文献

In einem bisher einzigartigen Großversuch wurde ein 16 m langer CFK-Spannbetonträger mit sofortigem Verbund experimentell untersucht. Ziel war es, die Biege- und Querkrafttragfähigkeit sowie das Verformungsverhalten von CFK-vorgespannten Bauteilen unter realitätsnahen Belastungsbedingungen zu analysieren, um den Einsatz nichtmetallischer Vorspannbewehrungen im modularen Brückenbau zu ermöglichen, siehe Beitrag auf S. 410–425. Der getestete Prototyp eines Modulträgers kombiniert CFK-Spannlitzen, CFK-Gitter und CFK-Stäbe und zeigt das Potenzial dieser korrosionsbeständigen Bewehrungen für den Einsatz im Brückenbau mit Fertigteilen. Die Ergebnisse dieser Untersuchungen wurden bereits erfolgreich für den Bau eines realen Brückenprototyps in Sachsen genutzt, der sich von September 2023 bis November 2024 im Rahmen einer temporären Bundesstraßenumfahrung bewährt hat. Die verwendeten CFK-Spannlitzen sind international langzeitig in realen Brückenbauwerken erprobt und industriell verfügbar und die Verwendung von modularen Fertigteilen ist international weitverbreitet und Stand der Technik. Der baupraktische Einsatz hierzulande sollte durch Erweiterung vorhandener Regelwerke und darauf abgestimmte Prüfverfahren für die Bewehrungsprodukte erleichtert werden. Nur dann ist eine einfachere Verbreitung dieser innovativen Bauweisen möglich. Der nächste Schritt kann mit der Überarbeitung der Richtlinie „Betonbauteile mit nichtmetallischer Bewehrung“ und deren geplanter Übernahme als Nationaler Anhang Deutschland der Neufassung des EC2 erfolgen. (Foto: HTW Dresden, Jakob Putz)

Collapse of the Carola Bridge in Dresden Part 1: From the ambitious design to the tragic partial collapse

September 11, 2024 will not only be remembered by the bridge construction community in Germany. The partial collapse of a prestressed concrete bridge without prior notice rightly made waves throughout society. The bridge in question is the Dresden Carola Bridge – an aesthetic and extremely slender structure that is justifiably regarded by experts as an engineering icon of its time, whose design and construction would still be a challenge under today's conditions. This first part of the article summarizes the history of the bridge's genesis, its design and construction, and presents the measures taken to maintain and renovate the structure. The second part, an attempt will be made to reconstruct the collapse process, and the search for the collapse causes will be described. In addition, the current monitoring will be discussed and an outlook on possible further action will be given.

Service life of structures considering consequence classes (CC) of failure: Tunnel constructions

The growing importance of the sustainable use of engineering structures necessitates innovative approaches to extend the service life and enhance the resilience of concrete structures. Aging, operational demands, environmental and climatic impacts present significant challenges, requiring a thorough analysis of quality and safety criteria to ensure the long-term functionality of these structures. The aim of this paper is to explore the application of identity and conformity methods for quality assurance in construction and evaluate their influence on the service life of concrete structures in critical infrastructure. Particular emphasis is placed on identifying safety margins and their potential contribution to extending service life. The paper includes an analysis of relevant design codes and the variability of material properties, with a focus on the coefficient of variation (COV) of concrete. In addition, the application of reliability-based safety concepts using partial safety factors is examined. These studies are intended to encourage a re-evaluation of current quality control practices, as well as the application of conformity assessments and acceptance testing for concrete structures.

The limits of the linear elastic ground in soil-structure interaction

Soil-structure interaction is a crucial aspect of structural analysis, relevant not only in the design of civil engineering structures but also in foundation systems of buildings, towers, industrial floors, and container terminal slabs. A key concern in this context is differential settlements, which act as imposed deformations on structures, affecting both the internal forces within the foundation system—such as the internal forces of a shallow foundation slab—and the stress distribution in the superstructure. To consistently account for these effects, the chosen soil-structure interface must be capable of accurately representing the distribution of differential settlements or the curvature of the settlement profile. In geotechnical engineering, advanced nonlinear material models are commonly employed to realistically describe the complex settlement behavior of soils. In contrast, structural engineering often relies on linear elastic approaches. This paper investigates whether a linear elastic parameter set (E, υ) can be defined for a uniformly loaded foundation slab that, under specific boundary conditions, satisfactorily reproduces the settlement distribution of a geotechnical nonlinear calculation.

Form factors for determining the electrical concrete resistivity on standard test specimens

The electrical resistivity of concrete can be a useful parameter regarding structural diagnostics or quality assurance in concrete production. Using a Wenner probe, for example, the apparent electrical resistivity can be determined, without considering heterogeneities or small specimen dimensions, with little effort on core samples from existing structures. The smaller the test specimens, the more the spread of the electric field is influenced, which can lead to misinterpretations. To avoid this, form factors are introduced in DIN EN 12390-19. However, these are only specified for a few test specimen geometries. In this article, form factors are derived by finite element methods and verified based on results from laboratory measurements and literature. Building on this, form factors for a variety of commonly used test specimen geometries are provided.

Monitoring of a highway viaduct via embedded fiber optic sensors

The condition of bridges is currently mainly assessed by means of periodic manual visual inspections. Additional structural health monitoring is primarily used when the structure is approaching the end of its service life. The installation of sensors is mostly costly, and changes can only be measured from this point onwards. Furthermore, extensometers or strain gauges provide local measurements only. In a pilot project on a busy highway in Austria, a new technology for bridge monitoring, which promises a paradigm shift in this regard, was investigated. Various fiber optic cables were laid in the formwork and embedded in concrete. Using various devices, which utilize different physical effects, fiber optic strain and temperature measurements were carried out during construction and after opening to traffic under dynamic excitation and traffic conditions. Processes such as concrete hardening, the lowering of the supporting structure, the release of the piers, the post-tensioning or the passage of trucks could be tracked closely. Strains and crack widths are measured along the entire length of the cable, even in areas that are not accessible, and can therefore considerably support visual inspections in the future. In the research project valuable insights into the advantages and disadvantages of different devices and the hurdles that stand in the way of a widespread application of the technology were gained.

Test methods for corrosion testing of reinforcing and prestressing steels

Corrosion is a primary damage mechanism in reinforced concrete construction, significantly reducing the service life of infrastructure. A categorisation of corrosion is imperative for the comprehension of the subject. The corrosion of concrete can be attributed to the carbonation process, whilst chloride-induced corrosion is prevalent in structures exposed to seawater or by de-icing salt. Additionaly to the former corrosion processe, prestressing steel structures could be also highly susceptible to hydrogen-induced stress corrosion cracking (SCC). In order to utilise alternative reinforcing steels, such as stainless reinforcing steel, it is necessary to ascertain the level of critical chloride threshold that can induce corrosion. Nevertheless, there is an absence of standardised test methods for determining this for the respective reinforcing steels to date. Acc. to current standardization, the sensitivity of prestressing steels to chromium content necessitates long-term ageing tests, which impede in-house production control due to the extended testing times. However, a newly developed test method using cathodic polarization, which has now been included in the latest draft of DIN EN ISO 15630–3, makes it possible to assess the susceptibility of prestressing steels to corrosion cracking within 24 hours. The results of this study will contribute to the improvement of service life estimation and the further development of standards for corrosion-resistant reinforcing steels and the robustness assessment of prestressing steels.

Novel 3D Reinforcements for concrete structures part 2: Material Development

With “Mesh”, an innovative, three-dimensional reinforcement structure made of carbon fibers, which can be produced fully automatically, new possibilities arise for construction and reinforcement concepts in concrete construction. After the first part of this publication series introduced the concept, development, and potential of this novel reinforcement technology, this paper summarizes the material characteristics determined through small-scale experimental investigations. The various process steps in the development of the reinforcement up to the final version are presented. In particular, the tensile load-bearing behavior of the reinforcement structure, investigated using fiber strand tensile tests, as well as the shape and compactness of the fiber strands formed the basis for selecting the preferred variant. Additionally, the test setup and obtained results are described in detail, demonstrating that the manufacturing method has a significant impact on the mechanical properties and quality of the reinforcement structure. In the upcoming parts of this publication series, further experimental investigations will be presented, focusing particularly on the bond behavior of the structure in concrete and large-scale component tests to analyze the shear load-bearing capacity.