Workshop on Structural Safety and Infrastructure Management Lloyd’s Register, London, 24th May 2017
Development of optical fibre distributed sensing for SHM of bridges and large scale structures A. Barrias1 *and J. R. Casas1 1UPC-BarcelonaTech Department of Civil and Environmental Engineering *
[email protected]
Distributed Optical Fibre Sensors Usually, the most practiced SHM approaches are based on electric strain sensors, accelerometers, inclinometers among others that present several challenges when applied to real world applications. As a result, optical fiber sensors (OFS), are one of the fastest growing an promising tools for the application on this field due to their inherent advantages such as stability, durability, small size and immunity to external electromagnetic interferences.
For the monitoring of large scale structures, the number of required sensing points that provides an accurate global behavior of the structure can increase rapidly, causing the increase of the associated costs and the complexity of the overall system. Distributed optical fibre sensors (DOFS), share the same advantages of the other OFS, whit the additional benefit of providing the ability of simultaneous and continuously monitor several thousand points, with the use of a single sensor, enabling a simpler and more cost-effective monitoring system.
Laboratory Experiments In order to investigate the bonding conditions and different implementation techniques, a three point load test was performed on two beams where a single DOFS with minimal coating was simultaneously embedded in the concrete and also implemented in the outside surface of the concrete.
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Real world applications As part of the secondment in the company COTCA S.A. the opportunity of witnessing in first hand the performance of this technology on real world structures arose. Here, DOFS were used in order to detect major changes in the structural behavior of a small viaduct located in Barcelona that underwent through rehabilitation works and, in this way, assess the structural safety during and at the end of this process. In the occurrence of strain and temperature variations in the monitored environment, the scattered signal within the fiber will change, thus achieving distributed sensing. There are three different scattering processes that can be produced in a DOFS, specifically: Raman, Brillouin and Rayleigh scattering. In this project , the study is focused on the Rayleigh based frequency domain reflectometry or Optical Backscatter Reflectometry (OBR) since it provides a better spatial resolution which enables damage detection.
Objectives of the project The general goal of this research is to contribute for a better and more cost‐efficient maintenance of the current infrastructure in operation allowing for an improved structural reliability. In this way and regarding the specific case of the sensors being investigated in this project, the most sought objectives are related with the study and analysis of the possible spatial resolution and strain accuracy obtained with optical distributed fiber sensors. Furthermore, the effectiveness of detecting crack or unusual deflections without failure or debonding of the optical fiber sensor are being investigated. For this, the most suitable bonding adhesives as well as alternative techniques of attachment of the fiber to the concrete or other structural elements of the monitored structure will be explored. Finally, the long-term reliability of these sensors measurements is also a topic of great importance that will be studied in this research project through the conduction of fatigue load cycling tests in the laboratory.
Through this application it was possible to experience the different challenges associated with the use of DOFS in real world scenarios, specially regarding the topic of sensor robustness and temperature effects on the sensor measurements.
Follow TRUSS ITN on The TRUSS project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 642453
www.trussitn.eu
