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- Cultural heritage (6)
- Radar (6)
- Structural modelling (4)
- Concrete (3)
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Organisationseinheit der BAM
ONSITEFORMASONRY is a research project funded by the European Commission under the 5. Framework Programme 1998-2002 in the Thematic Programme: Energy, Environment and Sustainable Development and the Key Action: The City of Tomorrow and Cultural Heritage.
The main objective of the project is the development and improvement of methodologies for the evaluation of the structure of historic masonry Cultural Heritages. For effective restoration and conservation of historic buildings, a detailed assessment of the structural safety and physical damages of the masonry structure is required. Therefore, typical masonry damages and the most frequent pathologies in each region have been identified and summarised in a catalogue of problems and damages. Selected non-destructive (NDT) and minor-destructive (MDT) techniques are performed by the partners including the development of software packages for fast and automated data analysis. The strategy for an effective and useful combination of different NDT and MDT methods will be worked out considering the results of case studies and taking into account the experiences of the consortium members. Recommendations and guidelines for the application of the integrated methodologies will be developed in close co-operation with end-users.
Ziel des von der Europäischen Kommission geförderten Projektes ONSITEFORMASONRY war die Entwicklung und Optimierung von Verfahren und Verfahrenskombinationen für die Bewertung der Struktur- und Materialeigenschaften von historischem Mauerwerk. Es wurden zerstörungsfreie und zerstörungsarme Methoden wie z. B. Radar, Ultraschall, Impact-Echo, Mikroseismik, aktive Thermografie und Flat-Jack weiterentwickelt und im Rahmen einer Vielzahl von Fallstudien vor Ort eingesetzt. In dieser Veröffentlichung werden die Ergebnisse des Projektes vorgestellt, und es wird auf weiterführende Literatur und Informationsquellen verwiesen.
Aufbau eines historischen Mauerwerkskörpers ("Obelix") zur Bewertung von zerstörungsfreien Verfahren
(2004)
Zusammenfassung
Auf dem Gelände der BAM entstand im Frühjahr 2003 ein Probekörper, der die Verbindung bildet zwischen Laborprüfkörpern und realen Bauwerken aus Mauerwerk. Er dient der Validierung und Weiterentwicklung von zerstörungsfreien Prüfverfahren zur Untersuchung von historischem Mauerwerk. Dabei wurde große Sorgfalt auf die Materialauswahl und den strukturellen Aufbau gelegt. Die Materialien sollten denen von realen, historischen Bauwerken entsprechen. Der strukturelle Aufbau ergibt sich aus praxisrelevanten Fragestellungen. Der Probekörper steht auch anderen Arbeitsgruppen für Verfahrensvalidierungen zur Verfügung.
Strategies and methodologies for the assessment of historic masonry structures based on non-destructive and minor-destructive testing methods were developed in the European Research Project ONSITEFORMASONRY and were successfully applied to assess the structure and material properties of selected structural elements in the Altes Museum in Berlin-Mitte.
For the planning of a broad reconstruction within the framework of a master plan concerning the whole of Museum Island in Berlin, several questions arose which are also typical for other historic structures in general, thus the Altes Museum was chosen as a pilot site for the validation of non-destructive testing methods.
Ultrasound sensors should be embedded into concrete for monitoring concrete properties. These new longitudinal wave sensors with a center frequency of 60 kHz were examined regarding their suitability for ultrasonic measurements in concrete structures in terms of emission characteristics, sensitivity and frequency ränge.
For the measurement of the radiation patterns, the sensors were embedded vertically and horizontally in concrete cylinders. The directivity pattern was measured using a laser vibrometer.
The sensitivity of the sensor was determined in water using different sensors of the same type. It shows changes in the signal amplitude as well as variations in the frequency ränge for different transmitter-receiver combinations.
The attenuation of the concrete affects the achievable resolution of the measurements and thus, the maximum possible spacing of the sensors within a concrete element. Experimental tests helped optimizing the distances with respect to the required resolution and the effort of embedding the sensors. The signal attenuation in the concrete was measured in the frequency ränge of 60 kHz in response to various degrees of reinforcement and grain size. For this purpose, the sensors were cast at different distances in the specimens studied. The recorded Signals were evaluated for their amplitude and frequency spectrum.
Building stones are porous media and they can deteriorate through moisture ingress and secondary damage such as crystallization of soluble salts. Not only is this due to the increasing number of flood events in the past years but also structural damages of houses from activity such as leakage or rising moisture (groundwater) are the main causes. The potential benefit of several nondestructive testing methods to assess water damage in building stone has been studied in a field-scale experiment. Three testing walls made of fired clay brick, sandstone, and spongilite were flooded and their drying behavior monitored using infrared thermography, complex resistivity, ground penetrating radar, and ultrasonics. The results were compared to the average moisture content determined by gravimetric weighing of the specimens. Qualitatively, the results of the different nondestructive testing methods matched well. But in terms of quantitative data, some scatter was observed and the results should be viewed with care. Collecting time-consuming calibration data would help to overcome this problem, but especially when dealing with historic building structures, this is not always possible in practice.
Muon Tomography of the Interior of a Reinforced Concrete Block: First Experimental Proof of Concept
(2021)
Quality assurance and condition assessment of concrete structures is an important topic world-wide due to the aging infrastructure and increasing traffic demands. Common topics include, but are not limited to, localisation of rebar or tendon ducts, geometrical irregularities, cracks, voids, honeycombing or other flaws. Non-destructive techniques such as ultrasound or radar have found regular, successful practical application but sometimes suffer from limited resolution and accuracy, imaging artefacts or restrictions in detecting certain features. Until the 1980s X-ray transmission was used in case of special demands and showed a much better resolution than other NDT techniques. However, due to safety concerns and cost issues, this method is almost never used anymore. Muon tomography has received much attention recently. Novel detectors for cosmic muons and tomographic imaging algorithms have opened up new fields of application, such as the investigation of freight containers. Muon imaging also has the potential to fill some of the gaps currently existing in concrete NDT. As a first step towards practical use and as a proof of concept we used an existing system to image the interior of a reference reinforced 600 kg concrete block. Even with a yet not optimized setup for this kind of investigation, the muon imaging results are at least of similar quality compared to ultrasonic and radar imaging, potentially even better. The data acquisition takes more time and signals contain more noise, but the images allowed to detect the same important features that are visible in conventional high energy X-ray tomography. In our experiment, we have shown that muon imaging has potential for concrete inspection. The next steps include the development of mobile detectors and optimising acquisition and imaging parameters.