Monitoring of a prestressed bridge girder with integrated distributed fiber optic sensors

Abstract

Several research projects carry out experiments on a newly built 45 m long research bridge, called openLAB. This contribution showcases the synergetic collaboration of the two research projects IDA-KI and smart_tendon in a joint experimental investigation on one of the openLAB’s 15 m long precast and prestressed girders, which was tested in a 4-point bending test prior to its installation into the bridge. The girder was equipped with distributed fiber optic sensors (DFOS) prior to casting, as DFOS provide detailed insights into the structure’s inner with unprecedented spatial resolution. The suitability of different installation methods for structural health monitoring applications from the beginning of the structures’ existence was studied. DFOS were either embedded in the concrete matrix, glued to the longitudinal reinforcement, included in prestressing strands in direct bond or inside strands of a post tensioned tendon. Robust DFOS with a monolithic cross-section, integrated directly into the concrete matrix, enable reliable crack monitoring and anomaly detection. DFOS integrated into tendons allow for efficient construction progress without the need for additional trades. Strain profiles in the linear elastic state can be accurately mapped. A transition to the cracked state is indicated by a disproportionate strain increase.