Investigation of measurability and reliability of adhesive-bonded built-in fiber Bragg grating sensors on steel wire for bridge cable force monitoring

The embedding method of fiber Bragg grating sensors (FBGs) has a significant impact on the measurability and reliability, as a result of the monitoring of FBGs depending on the strain transmission from the measured object. In this study, structural adhesive was used to join the FBGs with steel wire, and the relevant measurability and reliability of the adhesive-bonded FBGs with steel wire were investigated by loading & unloading cyclic test and fatigue test in the application of FBGs to monitor bridge cable force. It was found that there was a linear relationship between the load and the wavelength for both the loading and the unloading phases, and the data line from the loading process was parallel to that of the unloading process. In addition, 200 million fatigue cycles of steel wire decreased slightly the wavelength of FBGs when the steel wire was applied the same load. The differences in load vs. wavelength between loading and unloading phases, and with and without fatigue tests were likely attributed by the mechanical properties of steel wire, namely, the load-displacement curves of steel wire were responsible for the change in load vs. wavelength. Nevertheless, our experimental results indicated that the FBGs bonded steel wire using structural adhesive had an exemplary measurability and reliability, which will find more application in monitoring bridge cables.