Distributed Sensing Textile for Bridge Monitoring

Distributed Sensing Textile for Bridge Monitoring

In Phase I and Phase II, UMass Lowell team, collaborated with our industry partners, Saint Gobain (Textile manufacturer), have developed and tested a distributed fiber optic sensing system to monitor the strain and temperature variations on bridges. This system was installed by ARE (Sensor installation and bridge owner) on the Salmon Falls River (SFR) Bridge (Dover, NH) in 2019. The SFR Bridge is a lattice deck truss bridge with a span of 120 ft and a width of 60 ft. The optical fiber sensors are based on the principle of Brillouin Optical Time Domain Amplification (BOTDA) and Brillouin Optical Time Domain Reflectometry (BOTDR). These methods use the Brillouin backscatter signal caused by the nonlinearity medium of the fiber to measure strain and temperature changes. This approach is especially suitable for long-distance structural health monitoring since it provides distributed measurements along the entire fiber in the range up to 100 km with a spatial resolution of 1 meter.   In this presentation, our focus is on analyzing the response of the sensors during different seasons for complete validation of their performance, as well as studying the changes in the baseline.  As of now, the overall baseline is unchanged since October 2019, which indicates that the sensing system is still functioning very well. In addition, BOTDA and BOTDR signals were compared. This field test results demonstrate that the optical fiber sensors with the cost of a few hours’ installation could provide continuous monitoring for years. Taking advantage of the communication optical fiber network, the fiber optic sensing system could provide a good solution for future low-maintenance continuous real-time structural health monitoring.

As a complementary of the bridge monitoring techniques with permanently-installed sensors at discrete locations, remote sensing techniques such as video camera sensor and laser Doppler vibrometer can provide full-field and local  information of bridge dynamics with a portable and low cost nature. Phase-based motion magnification is implemented in processing the collected video data, and structural deflection information is extracted and analyzed. The extracted bridge dynamics, in terms of modal frequencies and operational deflection shapes, are mapped with the structural integrity. Comparison of the extracted frequencies and shapes shows a promising consistency with the fiber optic sensing modalities.