Two different existing structures monitored with distributed optical fiber sensors, are described in this paper. The principal Structural Health Monitoring (SHM) results of a valuable hospital rehabilitation (Sant Pau Hospital) and the enlargement of a prestressed concrete bridge (Sarajevo bridge), are presented. The results are obtained using a novel Distributed Optical Fiber Sensor system (DOFSs) based on an Optical Backscattered Reflectometry (OBR) technique. The versatility and easy installation of DOFSs compared with traditional monitoring systems is an important characteristic to consider its application in monitoring real world structures. The DOFS used in this study provide continuous (in space) strain data along the optical fiber with high spatial resolution in order of centimeters. Also and because the structural surfaces generally are roughness, the procedure to attach the optical fiber to two monitored structures are described. This is an important aspect because the influence in strain transfer between the DOFS and the surface is one of the principal parameters that should be considered in the application of the OBR technique.
Numerous works presenting information regarding the study of the potential of these sensors have been published in the last decade (Rodríguez et al. 2015 a,b; Palmieri & Schenato 2013) but very few showcase their application to real world structures. One of the various advantages of this technology is the easy installation to real life structures and the variety of them that can be instrumented with it. In both studied instrumentations the used fiber is based on a type of fiber optic in which the wavelength is established and compatible with a commercial data acquisition system. Each section of optical fiber has a maximum length of 50 meters and the union between the fiber and structural element (concrete/masonry) was performed using a twocomponent type epoxy adhesive. A coating of a polymer (polyimide) was used to protect the fiber against scratches and environmental attack.
Due to their particularities, each one of these structures underwent changes in their structural behavior without, nevertheless, ceasing to serve their purpose, i.e. accommodating patients in the case of the Sant Pau Hospital and the passage of vehicles and pedestrians in the case of Sarajevo bridge thanks to the application of these sensors. With the results obtained in this work, the OBR theory associated with DOFS proved its reliability in SHM of civil engineering applications and continues to showcase the promising future of monitoring systems based on this technology. -> Link to full text in repository
Palmieri, L. & Schenato, L., 2013. Distributed optical fiber sensing based on Rayleigh scattering. The Open Optics Journal, 7(1).
Rodríguez, G., Casas, J.R. & Villaba, S., 2015. Cracking assessment in concrete structures by distributed optical fiber. Smart Materials and Structures, 24(3), p.35005.
Rodríguez, G., Casas, J.R.. & Villalba, S., 2015. SHM by DOFS in civil engineering : a review. Structural Health Monitoring and Maintenance, 2(4), pp.357–382.