Concrete fatigue experiment for sensor prototyping and validation of industrial SHM trials

In this paper, preliminary results from a concrete fatigue experiment using a custom built machine are demonstrated. A pre-cracked concrete member is instrumented with bespoke metallic-bonded and epoxy-bonded fiber Bragg grating (FBG) displacement sensors, retrofitted over the crack. Fatigue loading is applied to the beam, with cycle magnitudes replicating results from a previous industrial trial concerning structural health monitoring (SHM) of a wind turbine foundation. Results are compared to an FEM model for verification. The new metallic-bonded crack displacement sensor design is compared in performance with the traditional epoxy-bonded design. Both sensors were sufficiently resilient under dynamic loading to successfully undergo 105 cycle fatigue test. The sensors display a linear relationship with respect to one another; however, from the initial thermal characterization of the devices between 20 and $65^{\circ}C$, the epoxy-bonded sensor exhibited considerable drift with every subsequent temperature cycle while the metallic-bonded construction was stable within the experimental error. The set up can be used over a long term to validate in situ results from distributed SHM sensors and for initial testing of sensors and data analytics strategies prior to any future field installations.