Strain monitoring in composite-strengthened concrete structures using optical fibre sensors

In this paper, the mechanical behaviour of the composite-strengthened concr ete structures is addressed. Optical fibre sensor presents a great deal of potential in monitoring the structural health condition of civil infrastruc ture elements after strengthening by externally bonded composite materials. The use of embedded optical fibre sensor for strain and temperature monito ring enables to reveal the status of the composite-strengthened structure i n real-time remotely. In this paper, an experimental investigation on the c omposite-strengthened concrete structures with the embedment of fibre-optic Bragg grating (FBG) sensors is presented. Single and multiplexed-point str ain measuring techniques were used to measure strains of the structures. Fr equency modulated continuous wave (FMCW) method was used to measure strains in different points of the structure with using only one single optical fi bre. All strains measured from the sensors were compared to conventional su rface mounted strain gauges. Experimental results show that the use of the embedded FBG sensor can measure strain accurately and provide information t o the operator that the structure is subjected to debond or micro-crack fai lure. Multiplexed FBG strain sensors enable to measure strain in different locations by occupying only one tiny optical fibre. Reduction of strength i n composite laminate is resulted if the embedded optical fibre is aligned p erpendicular to the load-bearing direction of the structure. (C) 2001 Elsev ier Science Ltd. All rights reserved.