Methods and Applications of Structural Health Monitoring on Bridges

Infrastructures such as bridges are subjected to cracks and damages in their service life due to oversized loading, fatigue and excessive usage. Structural health monitoring (SHM) has provided the tools for condition assessment of these infrastructures and investigate their behavior under various loads. In this research, application of fiber optic sensors (FOS) in damage assessment of bridges in addition to live load determination on bridges are investigated. A method for distributed crack detection along the entire length of bridges with various types is introduced. This approach is based on monitoring the distributed strains measured by the Brillouin scattering based optical fiber sensing technology. A damage index for identification of microcracks is introduced based on the normalization of measured and theoretical strains differentials. Validation of the proposed method is achieved by static load testing of a five span prestressed and post tensioned box girder concrete bridge. The method is further developed for the experiments subjected to dynamic loading. Live load determination of the bridge is achieved by development of a new bridge weigh in motion system for assessment of dynamic loads applied to the bridge. The proposed system is based on measurement of bridge abutment rotations and its correlation to the passing truck loads by means of rotational influence lines. Measurements of changes of girder rotations at the abutments are achieved by introducing a new rotation sensor. This sensor is an FBG based fiber optic sensor that correlates the changes of wavelength in the Bragg grating of the sensor to the rotational displacements of the sensor ends. The rotation sensors are then utilized in the BWIM system for individual axle weight detection in addition to GVW and truck speeds. Applicability and verification of the proposed system were put into test by a series of experiments on a four-span steel girder bridge and the accuracy of the system was evaluated by comparison of individual axle weights and gross vehicle weights of multiple calibrated trucks weighed at a nearby weighing station.