Filtern
Dokumenttyp
- Beitrag zu einem Tagungsband (6) (entfernen)
Schlagworte
- Concrete (4)
- GPR (2)
- Impact echo (2)
- Nondestructive evaluation (2)
- Ultrasonic (2)
- Ultrasound (2)
- Embedded sensor (1)
- Monitoring (1)
- Monitoring system (1)
- SHCC (1)
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.
Für Ultraschallmessungen in Betonbauteilen wurden neuartige radialsymmetrisch abstrahlende Longitudinalwellenprüfköpfe mit einer Mittenfrequenz von 60 kHz auf deren Eignung hinsichtlich Abstrahlcharakteristik, Empfindlichkeit und Frequenzspektrum untersucht.
Für die Messung der Abstrahlcharakteristiken wurden die Prüfköpfe vertikal und horizontal in Betonzylinder eingebettet und die Richtungsabhängigkeiten der Schallschnelle mithilfe eines Laservibrometers gemessen.
Die Streuung der Prüfkopfempfindlichkeit wurde im Wasserbad unter Verwendung verschiedener Köpfe gleicher Bauart bestimmt. Außer Änderungen der Signalamplituden zeigten sich auch Schwankungen im Frequenzbereich bei verschiedenen Sender-Empfängerkombinationen.
Die Schallschwächung des Betons hat Einfluss auf die erreichbare Auflösung der Messungen und damit auf die maximal möglichen Senderabstände im Bauteil. Durch experimentelle Untersuchungen und Simulationen erfolgte eine Optimierung der Abstände hinsichtlich des Aufwandes und der geforderten Auflösung. Die Signalschwächung im Beton wurde mit verschiedenen Impulsen im Frequenzbereich von 50 kHz bis 100 kHz in Abhängigkeit verschiedener Bewehrungsgrade und Korngrößen ermittelt. Hierfür wurden die Sensoren in unterschiedlichen Abständen in die Probekörper einbetoniert und die Empfangssignale hinsichtlich Amplitudenabfall und Frequenzspektrum untersucht.
An in-depth investigation of tunnel linings is performed at Eisenhower Tunnel, 60 miles west of Denver, Colorado, using a combination of four nondestructive testing methods: air- and ground-coupled ground penetrating radar (GPR), ultrasonic echo (US echo), ultrasonic tomography (UST), and impact echo (IE). A robotic frame with pneumatically operated vacuum plates is used to automate GPR, US echo, and IE. UST was performed manually. These techniques are used to identify and locate the reinforcement mesh and structural steel ribs. Local changes in ultrasonic phase are calculated by phase analysis processing techniques and apparent relationships between positive and negative phase shifts and steel and air interfaces are observed. According to previous laboratory research, these relationships indicate the bonded state between the concrete and the embedded steel, but without ground truth verification this can only be suggested. It is shown that this combination of methods can be used synergistically to provide tunnel owners with the layout and possible condition of tunnel lining reinforcement and structural components.
Tunnel lining evaluation is performed in the Hanging Lake Tunnel near Glenwood Springs, Colorado, using variations of four nondestructive evaluation (NDE) methods: air- and ground-coupled ground penetrating radar (GPR), ultrasonic echo (US echo), ultrasonic tomography (UST), and impact echo (IE). Potential regions of interest are identified using high-speed air-coupled GPR and visual inspection. A robotic frame with pneumatically-operated vacuum plates was used to automate the ground-coupled GPR, US echo, and IE tests, while the UST technique was used manually. This study shows that a particular combination of NDE techniques is a powerful tool for assessing the condition of tunnel linings and can detect potential anomalies such as delamination, depth of surface cracks, reinforcement depth and layout, and lining thickness. By mapping the phase shift of the ultrasonic pulses at detected interface, the potential bonding of layer interfaces and reinforcement is assessed.
The research project "Ultrasonic Net for Concrete Monitoring (UNeCOM)" aims at developing a methodology for an embedded ultrasonic network for the condition assessment of infrastructure constructions. Civil engineering structures made of concrete, which are located in tectonically active regions or undergo special loading conditions, may require continuous monitoring. It is important to assess the condition of the building and its stability to recognise and classify the effect of a seismic event or evolving damage at early stages before failure occurs. Embedded ultrasonic sensors offer the possibility to detect changes in the material and degradation mechanisms from inside the structure in areas which are difficult or impossible to inspect otherwise. In contrast to conventional ultrasonic testing methods, where the concrete surfaces are scanned with ultrasound probes, this new approach uses sensors, which are embedded into concrete, eliminating the effect of variable coupling conditions between sensors and concrete. This method allows an integral detection of changes in the concrete structure, for example due to seismic activities, to detect mechanical impacts, as well as degradation of the material due to overloading. Such methods have great relevance especially for the monitoring of constructions like power plants, bridges, offshore structures and other structures with high technical safety requirements. The sensor network can be controlled remotely through the internet which is also being used for data transfer. The embedded sensor network is designed to monitor structural damage and concrete degradation globally with high sensitivity.
Die Schallemissionsanalyse (SEA) ist ein passives zerstörungsfreies Prüfverfahren. mit dem Rissbildung, Risswachstum und andere Gefügeveränderungen delektiert und lokalisiert werden können. Anhand von zwei Beispielen aus der Forschung der Bundesanstalt für Materialforschung und -prüfung (BAM) wird gezeigt welche Möglichkeiten die SEA beim Bauwerksmonitoring und bei der Untersuchung von Baustoffen bietet. Im ersten Beispiel wird die Ortung von Schallemissionen zur Verfolgung des Risswachstums in Beton eingesetzt. Weiterhin wird mit Zugversuchen an Faserbeton illustriert, dass mit der SEA Versagensmechanismen identifiziert werden können.