NDT for need based maintenance of bridge cables, ropes and pre-stressed elements

Infrastructure is subject to continuous ageing. This has given life cycle management of infrastructure an increasingly important role. Reliable inspection and monitoring tools are therefore in demand. A reliable prognosis of the condition and behaviour of a structure is an important basis for an effective service life management. Furthermore, traffic loads and loads due to changing environmental conditions increased during the last years and will increase in the future. Repair and maintenance have to be performed, which requires reliable concepts and measurement of data, which is preferably gained through non-destructive methods. Furthermore, infrastructural constructions often have to be reconditioned when they are in use i. e. they cannot be torn down and rebuilt. Therefore, reliable diagnosis of the state of ‘hot spots’ is required. Within the frame of the Franco-German project FilameNDT steel wires of external tendon ducts and prestressing strands, prestressing rods, and stay cables are investigated. With regards to this field of application, practical relevance can only be gained when easily applicable and long ranging methods are used. The evaluation of extended structural elements using non-contact movable systems {bulk wave and guided wave application [Piezo, electromagnetic acoustic transducers (EMAT)], magnetic flux leakage (MFL), Micromagnetic methods} and those of localized elements based on elastic guided wave propagation—are complementary since they can be applied according to the various accessibility conditions of the tested objects. Inspection and monitoring scenarios were developed, hot spots were identified, and lab tests as well as field tests were carried out. A real cable stayed bridge in the Saarland region is available for monitoring within the frame of the project. Results from local investigations using guided waves and from monitoring field tests with micromagnetic sensors are presented and discussed. The results show the scenarios where the non-destructive methods are applicable and how the results can be used for structural health monitoring and maintenance concepts.

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