New fiber optic sensor for monitoring temperatures in concrete structures during fires

This paper proposes a new fiber optic sensor based on Regenerated Fiber Bragg Gratings specially designed to be embedded in concrete structures to monitor temperatures during fire events. A practical test was carried out on a 5.8 m long beam subjected to the ISO-834 fire curve for 77 min under the typical loads borne by beams in conventional structures. Nine optical sensors were installed at the mid-span section of the beam and were submitted directly to flames and high temperature gradients (of the order of 200 °C/min) that make them measure maximum temperatures of 953 °C. The temperatures recorded by the new sensors were compared with those obtained from electrical sensors (thermocouples) and a numerical model, with which they showed a good fit, except in those places in which concrete spalling caused distortions in the results and/or failure of the sensors. The paper thus demonstrates the viability of optical technologies in monitoring reinforced concrete during fires and analyzes sensor behavior to point out areas in which additional research is required.