Capabilities of a FBG sensor system to monitor the inelastic response of concrete sections in new tunnel linings subjected to earthquake loading

In a comprehensive experimental campaign, we investigated the capabilities of Fiber Bragg Grating (FBG) sensors in monitoring the inelastic response of new circular concrete tunnel linings, subjected to seismic events. The FBG sensors measured the strains of steel reinforcement to be treated by a decision support system (DSS). First, a set of four-point bending tests was performed on tunnel substructures, with the aim of characterizing the cross-section under cyclic loading and of designing an FBG sensor package for use in a unique full-scale test on a structure, which represented a complete circular section of the tunnel lining. Several types of FBG packages, to be embedded in and applied externally to the tunnel section, were tested to find the best solution. For comparison purposes, some standard devices were also used. The results of the experimental campaign are presented in detail, highlighting the performance of FBG sensors in reliable inelastic strain measurement of ductile concrete sections in seismic zones. Finally, the use of these data by a DSS allowed for the estimate of current structural conditions and damage at the monitored sections.