Field Testing of FBG Based Deformation Sensors Embedded in Concrete Bridge Structure

As far as the road network is concerned, bridge and tunnel structures are considered to be its most important and complicated elements. Bridges are completely exposed to environmental impacts; therefore, it is necessary to predict the actual structural health. The prediction can be based on monitoring of mechanical stresses which can be used to determine any resulting deterioration of load bearing structure. The main objective of bridge monitoring during construction phase is an observation of a structural behaviour in individual construction stages, particularly the actual mechanical stresses (or deformations) in critical cross sections. Based on the measured data it is possible to verify the designed parameters or to modify the design in following construction stages (load bearing structure dimensions’ adjustment, pre-stressing, loading of the bridge suspensions, etc.). After the construction completion, it is possible to observe the traffic intensity as well as deformations due to temperature changes, in addition to mechanical stress monitoring. This paper presents the initial phase of a field test dealing with the utilization of embedded fibre optic sensors (custom design) for monitoring the bridge structure. The load bearing structure of the bridge is pre-stressed continuous beam structure with three individual spans; this structure is replacing the old stone four-arch bridge, which was already in poor technical condition. The sensors are integrated directly into the load bearing elements; two different types of sensors were embedded into the concrete structure. The paper describes sensor design, installation, monitoring of the pre-stressing process and monitoring of stresses in several weeks after putting the bridge into operation. The two different types of Fibre Bragg Grating sensors were tested in laboratory conditions prior bridge installation. Testing is described and results are evaluated in the paper as well.tone four-arch bridge, which was already in poor technical condition. The sensors are integrated directly into the load bearing elements; two different types of sensors were embedded into the concrete structure. The paper describes sensor construction, installation, monitoring of the pre-stressing process and monitoring of stresses in several weeks after putting the bridge into operation. The two different types of Fibre Bragg Grating sensors were tested in laboratory conditions prior bridge installation. Testing is described and results are evaluated in the paper as well.