Einsatz von Ultraschallecho zur Spanngliedortung bei der Verstärkung von Brückenbauwerken - Externe Vorspannung der A7-Brücke über die B73 in Hamburg

Application of the ultrasound echo method for tendon duct detection for the strengthening of bridges - External pre-stressing of a motorway bridge in Hamburg

For strengthening pre-stressed bridges with external tendons, damage-free mounting of cradles and end anchorages is one of the major challenges during the reconstruction. Depending on the construction's utilization rate, even conventional reinforcement may not be allowed to be cut, not to mention internal tendons. Localisation of the latter may pose a particular problem, especially when it comes to detecting tendons in greater depths or behind strong reinforcement. A common example is the need to drill through T-beams for transversal pre-stressing of external anchorage blocks for load application. Common NDT methods like ground penetrating radar (GPR) might not be able to detect all ducts in every case. Hence, exploratory drilling or other questionable methods had to be used to minimize the chance of hitting and harming the reinforcement.
This article describes a possible solution based on the application of nondestructive ultrasound echo methods. Comprehensive tendon duct detections were carried out at a pre-stressed motorway bridge, which was the first bridge in Hamburg, which was ever strengthened with external tendons. This example exceeds the present state-of-the-art in applied NDT significantly. The results show the potential of the method for further use.