International Symposium (NDT-CE 2003)Non-Destructive Testing in Civil Engineering 2003
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Location of Prestressing Steel Fractures in Highly Reinforced Concrete MembersBernd Hillemeier, Technische Universität Berlin
Horst Scheel, Technische Universität Berlin
Since the end of the eighties the Remanence-Magnetism-Method is applied to civil engineering structures to detect prestressing wire breaks in concrete. The development of the method began with the detection of prestressing steel breaks in small reinforced prestressed concrete beams. In the beginning of the nineties the method was developed further for the application to post-tensioned concrete and has been constantly improved since that time. Now we succeeded in locating prestressing wire breaks surely also in unusually highly reinforced concrete units.
In the context of a research project a test stand with a very dense arrangement of mild reinforcement and tendons was built. The arrangement is similar to the arrangement of highly reinforced containments or the anchorage zone of large post-tensioned concrete beams. With the magnet and the process steps, which worked satisfactorily with normally reinforced concrete units, the location of prestressing wire breaks did not succeed with that extraordinary dense arrangement of reinforcement. The reason was, that the magnetic screen of the tendon by the mild reinforcement prevented a considerable magnetisation of the tendon. After the construction of a larger electromagnet specifically adapted to the high degree of reinforcement the magnetisation of the tendon behind the dense mild reinforcement succeeded. After a multi-level processing of measuring data, which represent certain magnetic states of the entire concrete unit, clear fracture signals come out and the wire breaks are thereby clearly identifiable the locations of built-in breaks.