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Einsatzbereiche des Meßsystems:
- Ortung von Strukturelementen oder Verdichtungsmängeln in Beton
- Dickenbestimmung von Bauteilen bei einseitiger Zugänglichkeit
- Messung des Haftverbundes bei mehrschichtigen Bauteilen
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- Automatischer Meßablauf durch Array-Technik
- Flexibler Einsatz durch lange Kabelverbindungen zwischen Prüfkopfarray und Meßapparatur
Trans-European corridors for transport of people and goods require strengthening of bridges to carry increased axle loads in terms of absolute axle loads and of their frequency. Most of the bridges along highways are reinforced or prestressed concrete bridges.
Since the late 1990s, CFRP laminates have been applied to box girder and T-beam bridges to increase the overall capacity. Although regular inspections are carried out, no special method was available to test the bond condition of CFRP laminates after being in Service for more than ten years. The German Center of Competence in Civil Engineering is aware of this need and funded a research project to investigate the bond condition by means of advanced non-destructive testing (NDT).
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.
For almost 15 years, carbon fibre-reinforced polymer (CFRP) plates and sheets have been used for strengthening and repair of civil engineering structures. CFRP plates were applied to upgrade structures for change in use or increasing traffic load. CFRP laminates have also been used to repair deteriorated structures such as multi-storey parking or bridges. The execution quality and condition of the strengthening measure in terms of bond integrity were neither monitored nor tested systematically. Inspectors eventually applied simple hammer knocking during regular main inspection for subjective noise distinction as a measure for eventual insufficient bond. This paper presents the feasibility and the limitations of low-frequency transversal ultrasonic waves with dry-coupling point-contact sensors for inspection and defect detection between CFRP laminate and concrete surfaces. The German Centre of Competence in Civil Engineering (DIBt) has initiated a national research project [Helmerich et al. (2012). Condition analysis of bonded CFRP-applications on concrete structures by means of non-destructive testing [in German: Zustandsuntersuchung von CFK-Klebeverstärkungen an Betonbauteilen mittels zerstörungsfreier Prüfung (ZfP)]. Final, internal project report], carried out at the Federal Institute for Materials Research and Testing (BAM), Germany. The aim of the project was to present a potential non-destructive testing method for bond defect detection as a measure for the durability of the strengthening system more than 10 years after application.
Inhalt ist die zerstörungsfreie Detailuntersuchung von Holzbauteilen mit einem dreidimensional abbildenden Ultraschall-Echoverfahren. Das neu entwickelte 3D-Verfahren berücksichtigt den anisotropen Aufbau des Holzes. Die Bildschnitte und Projektionen werden aus flächigen Ultraschallaufnahmen berechnet. Die Messungen erfolgen an Probekörpern sowie an Bauteilen aus der Praxis. In dem Forschungsvorhaben wird die für Holz neue 3D-Rekonstruktionsrechnung verwendet und mit dem Ziel weiterentwickelt, unter Berücksichtigung der anisotropen Struktur des Holzes eine dreidimensional aufgelöste Abbildung von Reflektoren im Inneren der Holzbauteile zu ermöglichen. Damit werden die bisher für Holzbauteile zur Verfügung stehenden Verfahren entscheidend ergänzt, weil nun eine hochgenaue dreidimensionale Abbildung erreichbar ist (Auflösung: 20 mm und besser).