German researchers have developed a method enabling prompt check-ups of the state of bridges without having to cause traffic disruption.
The newly developed ResoBridge method measures vibrations transferred from the bridge construction to its tensioning ropes to spot early faults and optimise maintenance planning.
The method is said to offer a more cost-effective alternative to current diagnostic techniques using ultrasound, radiography or magnet-inductive testing, which, apart from being rather costly, usually require the examined bridge to be at least partially closed for traffic.
Visual methods, on the other hand, are cheap but usually only reveal advanced damage.
The ResoBridge method is best suited for concrete bridges with external tendons that are not cast to concrete. Such bridges are equipped with a hollow concrete box underneath the road shielding the stabilising steel ropes. The new method uses an acceleration sensor to measure natural vibrations of these tensioning ropes, comparing the values immediately with 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,” explained Steffen Siegel from the Karlsruhe Institute of Technology, one of the method’s creators.
The method measures the frequency spectra with an accuracy of up to 0.01 Hertz. To detect changes, an initial value has to be determined as a reference. To streamline the workflow, the KIT researchers and their partners have developed and instrument to store the measured values for immediate frequency comparison.
The whole procedure including the assembly and disassembly of the sensor takes only a couple of minutes, with the whole examination requiring less than one day.
The team from the Karlsruhe Institute of Technology (KIT), who has created the new method, believes it could be successfully employed to assess the state of various facilities including hybrid towers and wind power plants.