Crack detection and retardation of steel structure by smart CFRP embedding PPP-BOTDA fiber sensors

Crack detection and retardation are essential issues in the CFRP reinforcement of damaged steel structures. A smart CFRP was developed for monitoring and retarding of crack opening displacement (COD) by embedding distributed fiber optical sensors which measure the strain singularity of externally bonded CFRP in the cracking zone. Based on crack-induced strain transfer mechanism in CFRP strengthening system, a theoretical model was then proposed to obtain an explicit COD expression considering both the elastic and elasto-plastic behavior of the adhesive. An experimental program of a pre-cracked pure bending steel element was also conducted to verify the proposed COD model. The distributed measurement of strain was conducted on CFRP by the commercial PPP-BOTDA (Pre-Pump-Pulse Brillouin optical time domain analysis) sensor with high spatial resolution. The comparison of theoretical CODs and the measured ones using EDDM (electronic digital display micrometer) confirms the ability of presented model on COD estimate. The proposed method using smart CFRP embedded with distributed optical fibers demonstrates great promise for high accuracy and sensitivity of COD monitoring, and has the capability of crack retardation and detection for the strengthened structures.