Combined static and dynamic monitoring of civil structures with long-gauge fiber optic sensors

Long-gauge SOFO® sensors have been in use for the last 10 years for the monitoring of civil, geotechnical, oil & gas and other structures. More than 3500 sensors have been installed worldwide in a number of different structure types. The original demodulation system is based on low-coherence interferometry and is particularly suitable for the monitoring of long-term static deformations. This paper reports the development and testing of a new sensing system based on Fiber Bragg Gratings and allowing the monitoring of both the static as the dynamic response of structures. The sensors are based on the well-proven SOFO packaging and allow the measurement of deformations over measurement basis of 2m, with a resolution of 1 microstrain and a frequency of 250 Hz. The system is insensitive to temperature variations, electromagnetic disturbances (electric power lines, lightning) and has demonstrated excellent long-term stability and durability. Each sensor also contains a temperature gauge, useful for the evaluation of the ambient parameters. This contribution describes the FBG-based MuST system, its functional principles and its performances in laboratory and field tests. The field installations include the monitoring of concrete bridges.