Performance of distributed optical fiber sensors embedded inside reinforced concrete structural elements
- Autores: Mattia Francesco Bado
- Directores de la Tesis: Joan Ramón Casas Rius (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2021
- Idioma: español
- Materias:
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- Resumen
The employment of a novel cutting edge strain monitoring technique named Distributed Optical Fiber Sensors (DOFS) as Structural Health Monitoring (SHM) tools is becoming increasingly common. Its popularity can be attributed to multiple reasons, the most important of which are the possibility of performing completely spatially distributed monitoring with sampling points at distances smaller than 1 mm, the high degrees of deployment configuration complexity thank to DOFS’ size and minimal stiffness, ease of deployment and resistance to Electro-Magnetic Interference, corrosion and extreme temperatures. Due to the inherent nature of SHM, though, up to now, the most common DOFS applications are the monitoring of already built structures and substantiation of their suitability to continue performing as per design. Consequently, most DOFS deployments see their bonding to the external surfaces of RC structures. A novel way of deploying DOFS that has taken hold in the later years consists in adopting DOFS to monitor the evolution of the strains present on the inside of a Reinforced Concrete (RC) structure i.e., bonding DOFS to the surface of embedded reinforcement bars (rebars) or embedding them directly in the concrete mass. Due to its recency, this application is characterized by an almost untapped potential pool. Indeed, SHM-wise, this continuous and highly sensible embedded monitoring system provides access to the ability of starting to detect deformations and damages as early as their appearance inside the structure (versus having to wait for their appearance on their external surface). This superior deformation and damage detection potential can very well help replacing the current time-based inspection model with one based on a performance or risk-based approach. As a consequence, today’s maintenance paradigm could shift from corrective to preventive, resulting in tremendous savings in infrastructure maintenance and a reduction of its associated social impact.
Yet, when deploying DOFS inside RC structures several phenomena may jeopardize the extractable results. Among these the non-neglectable possibility of fiber alteration/damage during the pouring of concrete and the possibility of erroneous measurements induced by the friction and/or clamping of the DOFS from the part of concrete aggregates. Whilst the deployment of DOFS with several claddings and coatings could compensate for these issues, the presence of a certain lag in the transmission of strains from the monitored surface to the DOFS’s silica core reduces the accuracy of the measurements and corrections are necessary to account for the strain lag between the fiber core and the substrate. For such applications, the preferable DOFS would be a thin, simply cladded, non-coated DOFS. In this case, though, the DOFS protective function against external SRA-inducing phenomena falls entirely on the adhesive layers with which the fibers are bonded.
The present thesis is aimed at improving the viability of coating-less DOFS deployments inside RC structures for Civil and Structural Engineering SHM. This objective is tackled with both a preventive approach and a curing one. The former is achieved by means of experimental investigation aimed at extracting methodologies and techniques that stem factors jeopardizing any DOFS-extracted strain measurement. The latter is achieved creating post-processing algorithms aimed at the cleansing of DOFS-extracted data of any data distortion and anomaly.
