Investigation on strengthening and strain sensing techniques for concrete structures using FRP composites and FBG sensors

This paper reports the results of an experimental investigation on the mechanical properties of the laboratory size rectangular concrete beams with the notch formation on the tension surface strengthened by using fibre reinforced plastic composites. Fibre-optic Bragg grating (FBG) sensors have been embedded at the interface between the concrete surface and external bonded composites to measure the strain variations when the strengthened structures were subjected to three-point bending load. Multiplexing strainsensing technique has been used for measuring the strains in different locations of the beam by using one single optical fibre. External bonded strain gauges were also attached on the surfaces of composites to measure the surface strain and the results were compared with that obtained from the embedded FBG sensors. The observation in the experiments showed that the flexural load capacity of the strengthened concrete beams was increased significantly after strengthening by laying-up the composite laminate for both plain and notched concrete structures. Debond and concrete failure occurred at the plate end region when the thick composite laminate was used. The embedded FBG sensors could provide the indication to the operator when the structure serviced in strange conditions. The strains measured at the interfaces from the sensors were higher than that from the surface bonded strain gauges in general.