Field tests of Fibre Bragg Grating sensors incorporated into CFRP for Railway Bridge strengthening condition monitoring

This paper reports results obtained from an unusual situation in structural monitoring – a ‘test-to-destruction’, measuring strain using a series of fibre Bragg gratings (FBG) sensors on a decommissioned concrete Railway Bridge in Örnsköldsvik, Sweden. The study formed part of the FP6 EU funded project ‘Sustainable Bridges’.

The FBG sensors were embedded in Carbon Fibre Reinforced Polymers (CFRP) rods incorporated into grooves specially created in the concrete cover of the bridge structure and interrogated using a compact system based on Wavelength Division Multiplexing (WDM). Throughout the study, the FBG sensors were continuously monitored, allowing the incremental increases in the strain to be seen and through the yield point of the carbon composite reinforcement.

The sensors were able to follow the resulting induced changes in strain of over a range in excess of 4000µε. The measurements made with the FBG- based system were found to be in agreement with the changes expected in the structure (together with the embedded reinforcement), produced by the loading applied.

The study has demonstrated the successful use of FBG-based technology pre-mounted in ‘smart’ carbon fiber composite reinforcements used in remedial repair and for monitoring better the performance of existing bridge structures.