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Vibrations Reveal State of Bridge Ropes

To guarantee safety of bridges, regular inspections are required. However, visual methods allow the damage to be detected in a rather advanced state only. Other methods such as ultrasound, radiography, or magnet-inductive testing are time-consuming and expensive. And, the bridges have to be closed to traffic.

The ResoBridge method developed by the KIT Institute of Concrete Structures and Building Materials (IMB) represents an inexpensive and reliable alternative. The patented method is suited for concrete bridges with external tendons that are not cast into the concrete. These bridges are equipped with a hollow concrete box underneath the road. Six steel ropes inside the box ensure stability.

The ResoBridge method is based on an acceleration sensor measuring natural vibrations of the tensioning ropes. The values measured are compared to results of earlier measurements. A decreasing frequency indicates decreasing tension of the rope. Significant changes of the values suggest damage of the wires or braids.

The instrument is easy to operate. Measurement of the values, inclusive of the assembly and disassembly of the sensor at the measurement point, takes a few minutes. The check of a bridge will take one day without the bridge having to be closed for the traffic.

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