Damage Monitoring Using Fiber Optic Sensors For The Joints Of Fiber Reinforced Polymer Structures

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Civil structures are the most important facilities for human activity, however, they usually have strong impacts to the environment of the earth. An alternative solution for this problem would be to use the maintenance-free long-lived, fiber reinforced polymer(FRP) composites which have high corrosion resistant, light weight and high strength characteristics. Actually, many FRP bridges and FRP framed architectural structures have recently reported The long-lived FRP structure is very attractive to do the periodical inspection of structural health and the damage identification after various natural disasters under the use of an innovative optical fiber sensors. The girders of Taylor Bridge in Canada have been reinforced with FRP material and installed fiber optic sensors.In this study, fiber Bragg grating(FBG) sensors were embedded in FRP structural members. First, the longitudinal tensile test of pultruded FRP strips have been performed and shown that the strain response measured with FBG sensors installed into the members is approximately the same as that with conventional strain gauges pasted on the surface of the members. Second, the longitudinal tensile tests of the bolted lap joints have been carried out ; the no-torque condition or a 45 N m torque has been adopted and the effects of frictional resistance have been discussed. Third, the FBG sensors were embedded beside the bolt on the transverse direction tension tests of the joints between a FRP structural member and a non-structural member using bolts. It is shown that the optical power decreases as the load increases, and its shape has two peaks after reaching at a critical load. When optical power spectrum has two peaks, the FBG becomes two different FBGs due to the occurrences of small transverse cracks inside the FRP material under locally large stress concentration beside the joint bolt.