Optic fiber sensor-based smart bridge cable with functionality of self-sensing

Bridge cables, characterized by distributed large span, serving in harsh environment and vulnerability to random damage, are the key load-sustaining components of cable-based bridges. To ensure the safety of the bridge structure, it is critical to monitor the loading conditions of these cables under lengthwise random damages. Aiming at obtaining accurate monitoring at the critical points as well as the general information of the cable force distributed along the entire cable, this paper presents a study on cable force monitoring by combining optical fiber Bragg grating (FBG) sensors and Brillouin optical time domain analysis/reflectory (BOTDA/R) sensing technique in one single optical fiber. A smart FRP-OF-FBG rebar based cable was fabricated by protruding a FRP packaged OF-FBG sensor into the bridge cable. And its sensing characteristics, stability under high stress state temperature self-compensation as well as BOTDA/R distributed data improvement by local FBG sensors have been investigated. The results show that FRP-OF-FBG rebar in the smart cable can deform consistantly along with the steel wire and the cable force obtained from the optical fiber sensors agree well with theoretical value with relative error less than +/- 5%. Besides, the temperature self-compensation method provides a significant cost-effective technique for the FRP-OF-FBG based cables' in situ cable force measurement. And furthermore, potential damages of the bridge cable, e.g. wire breaking and corrosion, can be characterized and symbolized by the discontinuity and fluctuation of the distributed BOTDA data thereafter accuracy improved by local FBG sensors. (c) 2012 Elsevier Ltd. All rights reserved.