Monitoring of a concrete arch bridge during construction

The Siggenthal Bridge is a concrete arch bridge with an arch span of 117 m, being built over the Limmat River in Baden, Switzerland. This bridge has been instrumented with 58 long-gage SOFO fiber optic deformation sensors, 2 inclinometers and 8 temperature sensors to monitor its deformations, curvatures and displacements during construction and in the long-term. The sensors have been installed successfully and the arch was monitored during the removal of the formwork and supports. It was therefore possible to observe the deformation of the arch when being loaded by its dead load and by the daily temperature fluctuations. The measurements have shown that the temperature changes produce deformations of the same order of magnitude as the dead loads. The out-of-plain displacements obtained by double-integration of the measured curvatures are in good agreement with the direct triangulation measurements. Monitoring was also carried out during the construction of the superstructure, with the associated change of the load distribution in the arch. This paper briefly introduces the functional principle of the long-gage sensors used in this application, illustrates their installation and discusses the measurement results obtained during the bridge construction.