Condition Monitoring of External Prestressing Tendons on a Concrete Multi-span Highway Viaduct

Abstract

In this paper, work on monitoring of the condition state of external prestressingtendons on a concrete multi-span highway viaduct will be presented. During the principal inspection of the motorway viaduct, an unusual» S wave« deformation shape of external tendons in a hollow viaduct deck was observed, which could represent an early sign of degradation processes inside the prestressing tendons. A detailed visual inspection of all external tendons was therefore performed, where four different damage states based on the deformation of tendon line were heuristically defined. The results of this visual inspection showed that more than 10% of tendons were graded with moderate or strong damage state. It was assumed that the incipient corrosion of tendons is present which results into the degradation of grouting and to local fracture of steel wires. Consequently, the axial forces of all tendons were assessed using vibration method to support the reliability analysis of the viaduct in case of different tendon fracture scenarios. The measurements of natural frequencies of external tendons showed that the loss of prestressing force cannot be exclusively attributed to the observed damage states of tendons. Finally, a contactless visual monitoring of prestressing tendons with 30 digital cameras was established to monitor the progression of variation of deformation line. After 4 month of monitoring no additional damage on tendons was observed.