| An optical fiber Bragg grating (OFBG) sensor system was investigated for highway bridge monitoring. The system is intended to complement existing bridge inspection methods. The data collected with the system will be ultimately used to assess the loading history, check the performance and alert for potential distress or failure and assess the effectiveness of repairs and maintenance programs.; The project was conducted in several phases: small scale specimen testing, large scale component testing and implementation in a full scale laboratory bridge to explore the feasibility and effectiveness of the sensor system.; In the small scale specimen testing, tension tests were performed to correlate strain from a Bragg grating sensor and a resistive strain gage prior to embeddement in concrete.; In the large scale component testing, artificial delaminations were simulated in large scale reinforced concrete beams during construction. The effect of these defects on the behavior, failure modes and ultimate capacities of the beams were evaluated using embedded single ended interferometric Bragg grating sensors.; In the full scale testing, forty-eight multiplexed Bragg grating sensors were integrated at the construction stage in an experimental full scale laboratory bridge. Thirty of the sensors were bonded to the tension steel in the slab, one was used as the room temperature monitor and seventeen were attached to the bottom flange of the girders. Thirty-nine foil gages were bonded next to the gratings for verification purpose. The strain data was obtained for the pristine structure, then damage was introduced near midspan of an external girder. Several levels of damage in the form of cut in the girder were imposed with the final cut resulting in a half depth fracture of the girder. The built in sensor system was used to monitor the real time after-fracture behavior in terms of load path redistribution and strain level changes in the structure.; Finite element models were developed to optimize the number of sensors and their locations. Static and dynamic tests were performed on the pristine and damaged structure. The finite element results agreed well with the experimental results (less than 5% error). |
