Structural integrity monitoring of reinforced concrete structures. Part 1: evaluation of protection systems for extrinsic fibre Fabry-Perot sensors

This paper reports on the use of extrinsic fibre Fabry-Perot sensors for strain monitoring of reinforced concrete columns and beams. The use of optical sensors in the concrete and on the rebar and column surfaces was made possible by the development of appropriate protection systems for the optical sensors. Two sensor protection systems were evaluated. The first involved the use of stainless steel tubing with flanges for the embedded sensors. In the second, the optical sensor was sandwiched between a four-layered prepreg that was either flat or had the shape of the rebar. A minimum of six Fabry-Perot sensors were interrogated on each concrete structure using a 16-channel optical channel selector unit and an optical spectrum analyser. Experimental results showed that, irrespective of the protection systems, the strain data from the Fabry-Perot sensors were in agreement with those obtained from the electrical resistance strain gauges. All the optical fibre sensors survived the structure manufacturing process and the majority of them survived up to the failure of the columns and beams. These experiments demonstrated that the sensor protection systems deployed in conjunction with the embedment methodology offer a reliable method for interrogating the mechanical integrity of concrete structures.