The security of civil
engineering works demands a periodical
monitoring of the structures. In many
civil structures
like bridges, tunnels and dams, the deformations are the most
relevant parameter to be monitored. Fiber optic
deformation sensors, with
measurement bases of the order of one to a few meters, can give useful
information both during the construction phases and in the long term. SOFO is a
structural
monitoring system using fiber optic deformation sensors. It is able
to measure deformations between two points in a structure, which can be from 20
cm up to 10 meters (or more) apart with a resolution of two microns (2/1000 mm)
even over years of measurements. The system is composed of optical deformation
sensors adapted to direct concrete embedding or surface mounting, the cable
network, the reading unit and the data acquisition and analysis software. The
system is particularly adapted to precise short and long-term monitoring of
deformations. The SOFO system is successfully used in a number of bridges,
tunnels, dams and geostructures. This paper briefly summarizes the measurement
principle of the SOFO system and presents two examples of application to the
monitoring of existing and refurbished bridges. The Lutrive concrete bridge was
instrumented with 40 sensors to monitor its curvature variations under static,
dynamic and thermal loading. From the curvature measurements and using a
double-integration algorithm it was possible to retrieve the vertical
displacements of the bridge. The Versoix bridge was instrumented with more that
100 sensors to monitor the different phases of its enlargement and
refurbishment. The sensors were used to characterize the interaction between
concrete of very different ages and to follow the horizontal and vertical
displacements of the bridge during construction, static loading testing and in
the long term.