Filtern
Erscheinungsjahr
- 2019 (29) (entfernen)
Dokumenttyp
- Vortrag (14)
- Beitrag zu einem Tagungsband (8)
- Buchkapitel (3)
- Zeitschriftenartikel (2)
- Dissertation (1)
- Posterpräsentation (1)
Schlagworte
- Concrete (29) (entfernen)
Organisationseinheit der BAM
- 8 Zerstörungsfreie Prüfung (20)
- 8.2 Zerstörungsfreie Prüfmethoden für das Bauwesen (18)
- 7 Bauwerkssicherheit (11)
- 7.3 Brandingenieurwesen (3)
- 7.1 Baustoffe (2)
- 7.6 Korrosion und Korrosionsschutz (2)
- 8.5 Röntgenbildgebung (2)
- 7.0 Abteilungsleitung und andere (1)
- 7.2 Ingenieurbau (1)
- 7.4 Baustofftechnologie (1)
Eingeladener Vortrag
- nein (14)
Fatigue is one of the most prevalent issues, which directly influences the service life expectancy of concrete structures. Fatigue has been investigated for years for steel structures. However, recent findings suggest that concrete structures may also be significantly subjected to fatigue phenomena that could lead to premature failure of certain structural elements. To date, fatigue of reinforced concrete has been given little focus. Knowledge on the influence factors and durability/capacity effects on this material should be improved. Current technological means to measure fatigue in civil structures like bridges and wind turbines (both onshore and offshore) are outdated, imprecise and inappropriate.
Meanwhile, this topic has got much more attention as time-variant loading on concrete structures plays an increasing role, e.g. in bridges with increasing traffic and heavier trucks, and for wind turbines for renewable energy production, e.g. for offshore wind turbine support structures affected by wind and waves.
The European Innovative Training Networks (ITN) Marie Skłodowska-Curie Actions project INFRASTAR (Innovation and Networking for Fatigue and Reliability Analysis of Structures - Training for Assessment of Risk) provides research training for 12 PhD students. The project aims to improve knowledge for optimizing the design of new structures as well as for more realistic verification of structural safety and more accurate prediction of the remaining fatigue lifetime of existing concrete structures.
First, the INFRASTAR research framework is detailed. Then it will be exemplified through the presentation of the major results of the four PhD students involved in the work package dealing with auscultation and monitoring. This includes the development and improvement of Fiber Optics (FO) and Coda Wave Interferometry (CWI) for crack sizing and imagery, new sensor technologies and integration, information management, monitoring strategy for fatigue damage investigation and lifetime prediction.
Construction methods, environmental stressors, and aging factors are the main causes for defects of reinforced concrete in nuclear power plants (NPP). These defects are typically occurred as corrosion of reinforcement steel, delamination, cracks, malfunction of post-tensioning or steel composite systems etc. Some of the challenges for assessing the performance of these structures by nondestructive testing methods (NDT) are that the assessment could be performed only during the annual overhauls when testing is time-limited and uncertainty of the accuracy and reliability of the available NDT testing devices combined with the lack of the international uniformity of the methods used for NDT tests. To overcome these challenges, a mock-up wall representing a section of the concrete containment of the NPP was built. The mock-up wall included simulated defects, which mimic the most common types of defects in NPP concrete structures such as dimensional errors, honeycombing, delamination, defects adjacent to the steel liner and voids in grouted tendon ducts for the post-tensioned structures. This paper introduces the design and construction of the wall including the concrete properties, reinforcement, tendon ducts and the types of the simulated defects. The paper also introduces the NDT methods and techniques that are suitable for assessing the condition of the mock-up wall under the real environmental conditions. These techniques include mechanical methods as rebound hammer, ultrasonic and electromagnetic methods. This mock-up wall will enable to investigate reliably available NDT methods and experts’ skills providing also an important and very much need educational platform for future NDE experts.
Sustainability means meeting the needs of today without compromising the needs of the next generations. How can we meet the needs of the next generations, if we do not even know what these needs are? If we do not listen to the next generation and learn from them? Do we even meet the needs of today for everyone on earth?
Durch das alkalische Porenwassermilieu ist Stahl im Beton vor Korrosion geschützt. Unter ungünstigen Umgebungsbedingungen (Karbonatisierung, Chlorideintrag) kann die passive Deckschicht auf der Stahloberfläche zerstört werden. Im weiteren Verlauf können sich korrosionsbedingte Folgeschäden, wie Risse und Abplatzungen am Bauwerk ergeben. Um notwendige Sanierungsmaßnahmen sind frühzeitige und weitgehend zerstörungsfrei ermittelte Informationen über das aktuelle Korrosionsverhalten der Stahlbewehrung von großer Bedeutung. Die Potentialfeldmessung ist ein etabliertes und weit verbreitetes Verfahren zur Beurteilung des Korrosionszustandes der Bewehrung in Stahlbetonbauwerken. Mit Hilfe dieses Verfahrens können Bereiche aktiv korrodierender Bewehrung zerstörungsfrei lokalisiert werden. In der Regel kommt diese Messmethode bei der Detektion chloridinduzierter Korrosion zum Einsatz.
The analysis of the chemical composition of cement-based materials like concrete is a crucial task in civil engineering. Concrete is a multi-phase material made of cement, water, aggregates, additives and admixtures. During the damage assessment of concrete structures, the external ingress of harmful species like chlorine, alkalis or sulfates needs to be determined. In order to provide a fast and precise analysis of concrete the application of LIBS offers unique possibilities as the technique can detect all elements at air atmosphere.
To determine the condition of concrete, the information about the chemical composition, the ingress of harmful species as well as the evaluation of characteristic values like the used cement type or the type of aggregates are needed. This work presents the two-dimensional evaluation of concrete samples using LIBS and multivariate data analysis of atomic and molecular emission. For the evaluation of the main components different classification methods will be applied to identify the heterogeneity of the samples. With respect to their specific phase, different species will be quantified using multivariate regression (PLS) and important figures of merit will be presented. All results will be verified using Standard procedure of wet chemistry (XRF, potentiometric titration and ICP-OES).
In earthquake-prone regions such as the Pacific Northwest, damage assessment tools are needed to enable safety evaluations to support recovery. Currently, damage assessment is performed primarily by visual inspection and is often impossible for structural members that are inaccessible, such as deep foundations or interior members hidden by cladding. This study explores the possibility of using embedded ultrasonic transducers to monitor reinforced concrete members for damage progression under earthquake loading. A novel methodology is proposed where changes in the member condition due to an increase in the earthquake-type loading of a full-scale column-foundation specimen are correlated with changes in the recorded ultrasonic waveforms. The discussed preliminary analysis of the ultrasonic signals is based on wave propagation velocity, changes in the coda wave portion, and maximum amplitude of the signals. Three embedded transducers were used to continuously monitor the laboratory specimen during destructive testing. This paper provides an overview of the proposed methodology, outlines the laboratory experiment, and discusses some preliminary observations.
Engineering Modelling
(2019)
This chapter presents the most commonly used approach to analyse the
thermo-mechanical behaviour of concrete structures subjected to high temperatures as in the case of fire loading. Prescriptions of the Eurocode are detailed for the thermal as well as the mechanical analysis. Finally, recommendations from two national (Austrian and German) guidelines give some improvements for Underground infrastructure.
Spalling of concrete due to fire exposure can lead to severe damage of building components. It is a much discussed subject in structural engineering and not yet completely understood. Generally, it is assumed that thermohydraulic and thermomechanical processes induce tensile stresses in the concrete. Furthermore, the tensile strength of concrete is reduced due to increasing temperatures. The combination of an increasing tensile stress and a decreasing tensile strength result in the occurrence of explosive spalling. The spalling behaviour of concrete is influenced by many parameters, for instance the water cement ratio, porosity, permeability of concrete as well, the presence of steel reinforcement and polypropylene fibres, also the size and geometry of the fire exposed area. Within the current research project at Bundesanstalt für Materialforschung und prüfung (BAM), the susceptibility to spalling of six different concrete mixtures is analysed to quantify the size effect using small scale, intermediate scale and full scale tests. A special fire test setup was built to test specimens simultaneously to enable a better comparability. All specimens are tested without additional mechanical load and unrestraint to prevent external induced cracking at the fire exposed site. Thermocouples are used to measure in situ the temperature distribution as an indication on the thermal degradation of the concrete during the fire tests. Afterwards the maximum spalling depth and the damaged area of the specimen are illustrated by a photogrammetric measurement system. The contribution to the spalling workshop presents the results of four concrete mixtures tested in intermediate-scale and full-scale fire tests. The comparisons are based on the concrete temperature as well as the obtained photogrammetric data. The results show that the spalling depth and the spalling area are significantly affected by the size of the fire exposed area.
Zahlreiche Schädigungsprozesse in Baustoffen stehen im engen Zusammenhang mit Feuchteeintrag und Feuchtetransport. Als Beispiel sind die schädigende Alkali-Kieselsäurereaktion (AKR) von Beton sowie Frost-Tauwechsel induzierte Gefügeschäden genannt. Zur zerstörungsfreien, ortsaufgelösten Feuchtemessung eignet sich die im Bereich der Geophysik etablierte, aber im Bauingenieurwesen noch wenig verbreitete, Messmethode der Nuklear Magnetischen Resonanz (NMR). Unter Verwendung der NMR-Relaxometrie sind sowohl Aussagen zum Feuchtegehalt und dessen räumliche Verteilung als auch die Charakterisierung der Porengrößen möglich, die das Transportverhalten eines porösen Materials maßgeblich beeinflussen.
Zur Erfassung der Mikro- und Mesoporen in Baustoffen ist dabei die Auflösung von kurzen T2 Relaxationszeiten unabdingbar. Bisher ist es mit gängigen NMR-Laborgeräten nur begrenzt möglich, solche kurzen T2-Zeiten schichtselektiv zu erfassen. Vor diesem Hintergrund wurde ein speziell für die Messung an mineralischen Baustoffen optimierter NMR-Tomograph beschafft. Dieser ermöglicht sowohl schichtselektive Messungen von Bohrkernen mit Durchmessern von bis zu 70 mm als auch bildgebende Untersuchungen an Proben mit Durchmessern ≤ 40 mm.
Erste Untersuchungsergebnisse an Sandstein, Tuffstein und Beton zeigen die Leistungsfähigkeit des neuen NMR-Tomographen zur Erfassung der porengrößenspezifischen Feuchteverteilung. In diesem Beitrag werden erste Ergebnisse verschiedenartiger Laborversuche exemplarisch dargestellt.
Für Sandsteine mit unterschiedlichsten Porengrößenverteilungen wurden mit dem neuen NMR-Tomographen und einem herkömmlichen NMR-System vergleichbare T2 Zeitenverteilungen ermittelt. Am sehr heterogenen Tuffstein konnten unterschiedlich poröse (und feuchte) Bereiche räumlich aufgelöst werden. Im Beton ließ sich der Feuchtetransport im Zementstein porengrößenspezifisch, schichtselektiv und zeitlich aufgelöst verfolgen.
Die bisher gewonnenen Ergebnisse zeigen das breite Anwendungsspektrum des neuen NMR Tomographen auf und ermöglichen ein besseres Verständnis des Feuchtetransports und der oft damit einhergehenden Schädigungsprozesse in Baustoffen.