Reference-Free Dynamic Distributed Monitoring of Damage in Multispan Bridges

The work presented pertains to the development and application of a damage detection method in bridges by use of distributed fiber-optic sensors. It utilizes the dynamic mode of the Brillouin optical time-domain analysis technique to measure distributed strains and to detect the locations of damage along the entire lengths of bridges. Unlike the current state of practice with distributed sensors, application of the proposed method does not require reference measurements. The practical ramifications of reference-free monitoring of bridges is significant because it eliminates the need for bridge closures. The method described in this article is applicable only when distributed sensors with dynamic measurement capabilities are employed. Two general approaches were considered and tested on two different bridges. Formulation of the method based on calibrated load tests led to a normalized crack index along the entire length of the bridge. The second approach corresponded to formulation of strain differentials and detection of damage under random traffic loads. Analysis of the results by the proposed methods and verification by visual inspections indicated that they were efficient in detecting the majority of anomalies in the bridges.