Performance of distributed optical fiber sensors bonded to reinforcement bars in bending

Abstract

Distributed Optical Fiber Sensors (DOFS) are optimal tools for mapping temperature, strain and vibration inside a structural element in two or even three dimensions. Thanks to their multiple sensing points, wide location range monitoring and customizable spatial resolution, the DOFS allow to paint a clear picture of the global behavior of a structure rather than reporting the tensile state of a limited number of points. This makes it ideal for the detection of deformations and cracking in reinforced concrete (RC) structures, crucial as a mean to ensure the safety of the infrastructure by identifying early signs of excessive damage and giving feedback on the structure’s ability to continue serving its intended purpose[1]. Yet, one of the main points holding back such technique are unexplained rise of anomalies in its readings beyond a certain point of any experimental test. Indeed, during multiple DOFS-monitored structural tests (Rayleigh scattering based), researchers have come across strain reading anomalies in the form of excessively large strain peaks with no physical meaning and veracity. The present paper outlines the results obtained by an experimental test developed in the UPC´s Structure Technology Laboratory with the goal of inducing such anomalies under different conditions in order to isolate and identify the cause of their origin. The test consists in gradually bending seven steel reinforcement bars with a DOFS bonded to their bottom tensile surface. The DOFS performance is then studied for different bonding conditions (different adhesives and their layering for every bar), for constant versus varying rebar sections (some incisions were performed in the rebars) and for different loading speeds (slow, fast and impact). In this paper important conclusions are developed which shed light on such phenomena and lay the grounds for an entirely anomaly-free DOFS-monitored test on RC ties planned as follow-up test.