Fiber Optic Sensors for Strain Measurement of CFRP-strengthened RC Beams

There is a growing need for built-in monitoring systems for new and aging civil engineering structures, due to problems such as increasing traffic loads and rising costs of maintenance and repair. Fiber optic sensors FOS), capable of reading strains, loads, deflections, and temperature are promising candidates for life-long health monitoring of these structures. However, since FOS have only been introduced recently into the field of structural monitoring, their acceptance and widespread implementation will be conditioned by their durability under severe climatic and loading conditions. This article reports on the performance of strain extrinsic FOS attached to carbon fiber-reinforced polymer CFRP) plates used to strengthen concrete structures. The specimens tested in this project are reinforced concrete RC) beams with an additional external CFRP reinforcement. The strain data obtained from the FOS were compared with data obtained from collocated electrical strain gauges. The FOS-instrumented beams were first subjected to fatigue loading for various numbers of cycles and load amplitudes. Then they were tested monotonically for failure under four-point-bending. The test results provide an insight on the fatigue and postfatigue behavior of FOS used for strain measurement in reinforced concrete structures.