Metal-packaged fibre Bragg grating strain sensors for surface-mounting onto spalled concrete wind turbine foundations

Abstract

In this work, we demonstrate preliminary results for a hermetically sealed, metal-packaged fibre Bragg grating strain sensor for monitoring existing concrete wind turbine foundations. As the sensor is bolted to the sub-surface of the concrete, it is suitable for mounting onto uneven, wet and degraded surfaces, which may be found in buried foundations. The sensor was able to provide reliable measurements of concrete beam strain during cyclic three-and four-point bend tests. The strain sensitivity of the prototype sensor is currently 10 % of that of commercial, epoxied fibre strain sensors.

Comparison of epoxy and braze-welded attachment methods for FBG strain gauges

“…Comparison between epoxy and braze-welded attachments for FBG strain measurement is not well documented. Commercially available sensor constructions are compared in [10], however internal designs of these are confidential. Effects of humidity on these attachment methods are unknown, yet this is of great interest due to the application of the sensors.…”

“…FBGs also boast a long-life capability and have been used extensively for strain and displacement monitoring in many industries, such as civil engineering [3][4][5], aerospace [6], as well as oil and gas [7]; most of which use epoxy based attachment methods. In previous work, brazed metal packaged FBGs [8] were used to monitor prestress in concrete [9] and for displacement measurement in spalled concrete [10].…”