Investigation into coaxial cable Fabry–Perot interferometers for strain measurement and crack detection in RC structures

Abstract

The coaxial cable Fabry–Perot interferometer (CCFPI) sensor is a promising technology for structural health monitoring, especially for large strain measurements. This study aimed to explore the possibilities of applying this technique to the strain measurement and crack detection in RC structures. First, a distributed CCFPI sensing system was developed that was used for signal processing and data collection. Subsequently, four- and three-point bending tests were carried out on RC specimens. In the tests, separate methods were proposed for fabrication, encapsulation, and installation of a CCFPI sensor on RC structures. The CCFPI sensors were separately adhered to the rebar, embedded within the concrete volume as well as bonded at the bottom surface of the test specimen, and their performance regarding distributed strain measurements, crack detection, and quantification, was investigated. Findings from the tests have demonstrated that CCFPI sensors can measure the developed strains from the initial loading, cracking, and from the yielding to the crashing of the RC structures. Some systematic errors resulting from calibration were observed in the quantitative comparative data, and accurate calibration is crucial to improve the measurement accuracy. The results also exhibit the capability of CCFPI sensors for crack detection and crack width determination.