SHM of wire- breakage in concrete bridges by Acoustic Emission Technique

Abstract

A lot of prestressed concrete bridges in Germany with an age of 50 years and more are showing problems due to an unseen increase of heavy traffic and/ or insufficient construction. A few years ago, it was recognized and stated by the government in Germany, that some steel charges used for the tendons of older prestressed concrete bridges tend to Stress Corrosion Cracking (SCC). This can be critical, because a sudden catastrophic failure of a tendon is possible. The inspection of the tendons, which are embedded in the concrete, is very difficult. There is no ndt- method available for a sufficient assessment of such tendons. It had been shown, that one third of all wires in a tendon have to fail, before visible cracks can be observed from outside. This is too late for a reasonable assessment of such a bridge. A structural health monitoring system (SHM) is needed. Actually more than a dozens of bridges are monitored for wire- breaks in Germany and it will be getting more in the future. Extensive investigations to this subject were undertaken or still in progress. One of the outcomes is, that Acoustic Emission (AT) is the only useable ndt- method for detecting wire-breaks during the service- life of the bridge. Furthermore a guideline is in preparation and nearly finished in order to do a monitoring for wire-break detection in prestressed concrete bridges with Acoustic Emission. This guide is written by civil engineers, bridge responsible/ owners and Acoustic Emission Specialists.