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The Assignment:
A construction company called us up recently to enquire whether it was possible to locate the exact position of tension tendons in an older bridge which they had been contracted to reinforce using  0.5 centimetre thick metal bands.  Tension tendons are worked into the concrete of  bridges to increase their structural integrity. If these tendons are damaged while drilling is being carried out, for example, then this could greatly affect the strength and stability of the whole structure.

The Project:
The construction work which the company had been contracted to do was to be carried out on a bridge with two traffic lanes. This meant that traffic had to be first restricted to one lane while engineers from VDL commenced with carrying out the necessary measurements on the underside of the bridge. The team of engineers worked in shifts during the day and throughout the night to locate the tension tendons in the concrete layer of the bridge’s structure.

The video footage and the images below show just  how the team of experts from VDL went about locating the tendons. The photos also show how holes were drilled prior to the fastening of the metal bands that were intended to improve the stability and strengthen the structure of the ageing bridge.

The Technology:
The engineers at VDL used georadar (1.6 GHz), a non-destructive form of inspection that is excellently suited for locating the position of objects like reinforcements in concrete, to determine the exact position of the tension tendons.

Georadar (impulse radar) is based on an electromagnetic measuring method which involves sending out short electromagnetic impulses in a frequency range between 400 MHz and 1.6 GHz into a particular surface or building component on which an inspection is to be carried out. The impulses are then reflected or transmitted, depending on the character and properties of the materials and the type of antennas that are employed.

The frequency range of the type of antenna used in the inspection and the physical parameters of the surface that is being inspected also determine how deep the georader (impulse radar) penetrates into the material. As a rule, inspections can be carried out up to a depth of six metres using this measuring method.

If you would like to know more about this particular measuring method, feel free to visit our website or contact us on +49 (0) 24 52 962-140. You can also send us an e-mail at messtechnik@vonderlieck.de.


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