LOW-COHERENCE DEFORMATION SENSORS FOR THE MONITORING OF CIVIL-ENGINEERING STRUCTURES

An optical-fiber deformation sensor with a resolution of 10 mu m and a n operational range of 60 mm has been realized. The system is based on low-coherence interferometry in standard single-mode telecommunicatio n fibers. It allows the monitoring of large structures over several mo nths without noticeable drift. No continuous measurement is needed and the system is insensitive to variations of the fiber losses. This tec hnique has been applied to the monitoring of a 20 m x 5 m x 0.5 m, 120 ton concrete slab over six months. It is possible to measure the shri nkage of concrete and its elastic coefficient during prestraining, giv ing reproducible results in good agreement with theoretical calculatio ns and measurements performed on small concrete samples. This paper de scribes the optical arrangement and the procedures used to install opt ical fibers in concrete.