Resumen de Monitorización de estructuras de hormigón mediante sensores de fibra óptica distribuida
This doctoral thesis presents the use of an opto-electronic system so-called OBR (Optical Backscattered Reflectometer) as an alternative of measurement in structural health monitoring (SHM) processes in concrete structures, which may present cracks even for service loads.
The main feature of the OBR system is its great sensitivity and high spatial resolution through the use of an optical fiber cable as a sensor, which is called the distributed optical fiber sensor (DOFS). Thanks to that, it becomes possible to obtain strain records where the presence of cracks can be identified and localized. Thus, the experience of an earlier application is first taken up and a method of calculating average crack width in concrete structures subjected to bending is proposed and it is based on information from the strain records obtained with the OBR system.
Afterwards, the OBR system is applied to the study of three partially pre-stressed concrete (PPC) beams of 8 m in length and subjected to shear stress. These beams were instrumented both in conventional form with discrete sensors, and with a DOFS adhered to the surface. Based on the experimental results obtained, the capacity of the OBR system to monitor concrete structures subjected to shear is evaluated, and a method is proposed to detect, locate and subsequently quantify the average shear crack width.
One of the three beams tested to shear and already with the presence of cracks along its entire length, is tested to flexion. In this test it is evaluated the system ability to detect the presence of existing cracks, and the appearance of new cracks. Once the main cracks have been detected and localized, the proposed method of calculating average crack width is again applied and the results checked.
Finally, the application of the OBR system to a real structure is carried out. The above consisted in the monitoring over almost eight months of the process of enlarging a two-span pre-stressed concrete bridge with a total length of 86 m. In this application, the effects of temperature were an important factor and their correction was taken into account for a correct interpretation of the obtained data.
Finally, based on what was observed through the information obtained in each of the previous cases, some conclusions are established regarding the advantages and disadvantages of this type of opto-electronic measurement systems based on the use of DOFS in the SHM of concrete structures. The main conclusion is that the method proposed in this thesis achieves a very satisfactory and promising results regarding the detection, localization and quantification of cracking both in bending and shear in concrete structures in the range of normal service loads.
