Deformation monitoring in prestressing tendons using fibre Bragg gratings encapsulated in metallic packages

Abstract

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Identifying fabrication defects of metal packaged fibre Bragg grating sensors for smart pre-stressing strands

“…They were attached to four steel prestressing strands to be inserted into two concrete beams for a long term assessment of the sensors performance and their practical application. The FBG encapsulation method applied has been previously documented [3], [10]. To summarise, type-I FBGs written in copper alloy coated optical fibre were induction brazed into metal capillaries.…”

First-time demonstration of measuring concrete prestress levels with metal packaged fibre optic sensors

“…For each sensor the point at which the slope of the line of best fit changed was different; however, it was always in the 100-150kN range. Whilst testing with a single metal rod this characteristic was not seen and the strain sensor response was linear up to stresses of 1300MPa [23,22] (equivalent to approximately 300kN in the pre stressing strands). This shows that possibly the strain sensors cannot be reliably calibrated by the total force measured at the end of the 7-wire strand.…”

“…It has been shown previously that the sensors can survive while being attached to single wires subject to 1300MPa equivalent to 300kN for the 7-wire strands [23,22]. For this reason, frictional effects on the distributed force of the strands could not be investigated.…”

“…The sensor fabrication process for this test has been previously documented [21,22]. Fibre Bragg gratings, written in metal coated fibre, were brazed into 25mm metal capillaries using an induction coil in order to mechanically and chemically protect them from the environment.…”

Preliminary characterization of metal-packaged fiber Bragg gratings under fatigue loading

“…Our recent work related to the high stress monitoring of prestressing tendons employing the developed technology demonstrated an improved performance over the epoxy or electroplating-based strain monitoring systems [14], [15].…”