On-site validation of fiber-optic methods for structural health monitoring: Streicker Bridge

Structural health monitoring (SHM) has potential to facilitate understanding of real structural behavior and provide important information for assessment of structural safety. In spite of its importance and its promising benefits, SHM is scarcely used on real structures. An efficient approach for implementation of SHM has not been developed yet, which is in part due to the current inefficient fragmented approach to SHM in research activities, in practical applications, and in education. To address this challenge, a holistic approach is taken in creation of novel fiber-optic methods for strain-based SHM, with an overall objective to achieve Level IV SHM. The methods are researched, applied, and (to the extent of feasible) validated through implementation on Streicker Bridge at the Princeton University Campus. While the presented research consists of several components, they are all mutually connected by the holistic approach and the ultimate objective. Thus, this paper presents for the first time the holistically researched methods and their validation in on-site conditions. The methods are first generally presented and then their implementation is illustrated through the application to Streicker Bridge, including design of sensor networks, algorithms for data analysis, and rich information on structural conditions provided by the SHM. Two fiber-optic methods are currently applied to the bridge: a global structural monitoring method based on discrete fiber Bragg-grating long-gauge strain and temperature sensors and an integrity monitoring method based on Brillouin-scattering distributed sensors. The results include early age and long-term strain evolution, damage detection, and characterization, including thermally induced cracks and evaluation of reduced joint stiffness, structural identification, evaluation of the effectiveness of complex cross sections through the determination of the location of the centroid of stiffness, discussion of bending, shear, and torsional cross-sectional stiffness, and determination of natural frequencies. This research demonstrates that the proposed methods can be used reliably in on-site conditions to achieve Level IV monitoring. The presented fiber-optic methods can be applied universally to a wide range of beam structures, and the results presented emphasize their effectiveness.