Distributed strain sensing for civil engineering applications

The ability to monitor the long-term performance of engineering structures accurately and efficiently is an extremely valuable one. The potential benefits of structural monitoring include reduced lifetime maintenance costs, improved safety and the ability to confidently use more efficient designs and advanced materials. This thesis presents some of the results of a research program conducted at the University of New Brunswick intended to develop advanced sensor technology for structural monitoring applications.; The sensor system developed at UNB is a distributed fibre optic strain sensor based on Brillouin scattering which allows the strain in a structure to be measured by embedding or attaching a fibre optic cable to the structure. In contrast to more conventional sensor technology, the fully distributed nature of the system allows measurement positions and gauge lengths to be determined at measurement time, rather than at installation time. This provides unparalleled flexibility of data acquisition capability to engineers.; Experimental tests were conducted on a number of different structural members to verify the performance and applicability of the sensor system. Various sensing fibre configurations were used, ranging from simple layouts with a few discrete measurement locations to truly distributed layouts allowing dynamic measurement position selection. Early tests performed using 400 mm spatial resolution had measurement accuracies of better than ±50 μϵ, with good agreement between the measured sensor data and theoretical predictions. Further development of the system improved measurement accuracy to better than ±10 μϵ when using 500 mm spatial resolution. The ultimate strain measurement accuracy of the system was experimentally found to be better than ±5 μϵ, with the exact figure depending on a number of variables in both the system design and its operating conditions. Outdoor testing of the system was also done to investigate the issues associated with thermal effects on the strain measurements. While the preliminary trials did not prove entirely successful, the results demonstrated that thermal compensation of the system should be possible.