Performance Evaluation of FBG Sensors under Fatigue and Weathering

Structural health monitoring (SHM) techniques are often used for detecting damage and diagnosing the structural conditions. There are many issues related to installation and constructability of SHM systems and in-situ installation of fibre optic sensors (FOS) on rebars in reinforced concrete (RC) elements. Here, a solution is provided for installation of a FOS strain sensor by mounting it on a supplementary bar a priori and then attaching it to the main reinforcing bar of interest at the construction site prior to concrete pouring. Such innovative deployment system for FOS is particularly advantageous for developing a practical SHM system for infrastructure. However, the performance of such systems under various loading and climatic conditions is not very well known. The objective of this research is to assess the performance of the said system used in concrete beams reinforced with FRP (fibre-reinforced polymer) bars, under normal and adverse environmental conditions such as, immersion and cyclic immersion in alkaline solution. The results show that the proposed FOS system is efficient and useful in capturing the real strain in control, and wet and dry conditions. Electric strain gauges were found to perform poorly in adverse conditions. Record of the entire response of the structure to external loads of a structure makes it possible to identify and analyze periodic events. It helps a better evaluation of the acquired data. The data collected over a period of time provides valuable information and helps forecasting future structural behavior and estimating risk. In general structures are observed objectively only a continuous monitoring of structural loads and stress cycles can reflect actual structural characteristics.