Reference-free distributed monitoring of deflections in multi-span bridges

The research presented herein pertains to developing a reference-free technique for monitoring bridge deflections under operational conditions. The method is based on monitoring the distributed strains along the length of bridges and employing the Inverse Finite Element Method (iFEM) to compute the deflection for the entire length of bridges. Distributed sensing of strains was achieved by a Brillouin Optical Time Domain Analysis system (BOTDA). The dynamic strains were then used in the iFEM algorithm to calculate the deflections of the structure. This approach computes structural displacements by a variational principle with minimal computational cost. Because of its independence from loads and material properties, the proposed methodology monitors the dynamic deflections during bridge routine traffic operations, and it is potentially viable for real-time monitoring. The approach is validated through two comprehensive case studies, including a laboratory experiment and a field application on a multi-span concrete bridge.