Evaluation of a large-scale bridge strain, temperature and crack monitoring with distributed fibre optic sensors

Many structures like bridges are ageing and the necessity to measure the uncertain parameters is relevant. Crack-related parameters can be measured with traditional techniques like crack gauges and displacement transducers. A method that can detect and localise cracks as well as measure crack width is most favourable. Several distributed and quasi-distributed systems were introduced to the market and tested in recent years. This paper presents a large-scale Structural Health Monitoring project based on stimulated Brillouin scattering in optical fibres for an old bridge. The Gotaalv Bridge is a continuous steel girder bridge with concrete bridge deck. Steel girders suffer from fatigue and mediocre steel quality and some severe cracking and also a minor structural element collapse have taken place. The system installed on the bridge measures strain profiles along the whole length of the bridge and detects cracks that are wider than 0.5 mm. Procedures like factory acceptance test, site acceptance test, laboratory testing and field testing are presented and analysed. Innovative technology was developed, tested and applied on the bridge. Heuristic knowledge was collected; conclusions are presented and discussed for future development.