The use of Optical Backscatter Reflectometer (OBR) as a distributed fiber optic system to measure strain and detect cracking in concrete structures is investigated. A laboratory experience in a concrete slab is first presented and after this pilot test, a full-scale bridge load test was used to investigate the effectiveness of the OBR technology monitoring system when applied to real structures. The bridge monitoring consisted of the installation of 100m of optic fiber in the soffit of the prefabricated bridge beams. Strain readings obtained from the optic fibers were compared to results from previous identical load tests applied to the bridge, confirming the high accuracy inherent in the optic fiber technology. Subsequently, the cooling tower of a power plant was monitored using the OBR sensor system. A total of 300 meters of cooling tower are monitored and 30,000 points on the concrete surface (inner and outer of shell) are interrogated. The obtained results show the feasibility of this technique despite the roughness of the
concrete surface and the heterogeneity due to the presence of aggregates of different
sizes. All applications verify that the OBR sensor is not only able to detect appearing
cracks that are hardly visible, but it is also able to perform robustly and with high
accuracy up to a load level producing a crack width in the range of 1 mm. Moreover,
the OBR frequency signal is acquired properly and provides correct strain values without breaks, even at a high load level. Regarding economic impact, deployment of the
OBR monitoring system presents a financial advantage over equivalent monitoring techniques (number of points interrogated).
Villalba, S.; Casas, J.; Aparicio, A.; Villalba, V. ASCE. Journal of bridge engineering Vol. 18, num. 11, p. 1174-1188 DOI: 10.1061/(ASCE)BE.1943-5592.0000450 Data de publicació: 2013-11 Article en revista
The objective of this research has been to design, develop, and evaluate experimentally a modified type of construction joint of limited length between concrete slab segments. The design concept is based on an anchorage hook of reduced development length stiffened by transverse reinforcement bars. The purpose of this paper is to investigate the mechanical behavior of the joint in terms of stiffness and strength for an application that requires high durability, which often leads to serviceability problems such as cracking and water leakage at transverse joints. This can regularly appear in bridges. Additionally, bridge decks are structures that are subjected to repeated loading such as traffic loads, making it necessary to evaluate the behavior of joints under fatigue load. Therefore, studies focusing on the strength, stiffness, and serviceability of the joints must be carried out. This paper investigates experimentally the fatigue behavior and strength of loop joints with regard to the loop bar diameter, loop joint width, and applied load ranges. These results were compared with the behavior of RC slabs without joints. A total of eight slabs were fabricated for fatigue loading tests, and the failures of the different specimens (with loop joints and without) were obtained. From the test results, the mechanical behavior of the slabs with loop joints was confirmed to be similar to that of the slabs without joints. The experimental loop joint design was found to perform correctly under fatigue loads.
Se presenta la aplicación en un viaducto de un sistema de monitorización continúo (en el espacio y tiempo) de fibra óptica (OBR) que suministra datos a tiempo real para poder controlar y conocer el estado/comportamiento de la estructura. Se confirma la viabilidad del pegado de los 100m de fibra óptica sobre la superficie de hormigón y la lectura continua durante el periodo de investigación. Se obtienen lecturas de deformación y se comparan con las obtenidas en las pruebas de carga realizadas, confirmando la precisión de la tecnología (+-1 με). Gracias a esta precisión y a una resolución espacial de 10 με, el sistema
propuesto aporta ventajas importantes respecto a otros equipos de monitorización de fibra óptica. La medición continua de deformaciones a lo largo de toda la longitud de la fibra permite además obtener las flechas. Se presentan los resultados obtenidos de la monitorización a tiempo real, como también futuras aplicaciones del sistema en otras obras de ingeniería civil y edificación.
This paper provides an overview of the techniques based on fiber optics sensors to assess the condition of existing bridges, in order to enhance their durability, increasing lifetime and reliability and decreasing maintenance activities. Application of these sensors to monitoring strain, temperature, load measurements, corrosion and cracking of reinforced and prestressed concrete structures is described. The possibility to embed these small and unobtrusive sensors in composite materials, used in the strengthened of old bridges, is also highlighted.
When a bridge is projected, not only it is pursued the good design and quality in the construction, but also a safe and long-lasting exploitation of the structure. Obviously, the safest structures and the more long-lasting structures are those which are usually managed. Therefore, the monitoring performs an essential role in the structural management. The most important stage of a bridge is its period of service. During this stage, the structure can be repaired or modified depending on the existent needs at that moment. By monitoring the structure, it is possible to obtain data at real time, data which allow us to know the behaviour of the structure and, consequently, allowing us to plan a possible action. Therefore, the advantages of the monitoring at real time are obvious: it improves the structural management, increases the structural safety and allows to follow its behaviour. The paper deals with the development of an integrated system of monitoring and control of post-tensioned strands based on the use of optical fiber sensors. To obtain such a monitoring technique is of great relevance since, lamentably, at present still does not exist any reliable method to monitor the long-term behaviour of post-tensioned strands in concrete structures. Being able to monitor the displacements / deformations that are produced in each of the peripheral wires that form the strand, it is possible to detect a possible area of corrosion and simultaneously to obtain information of the tension redistribution in case of break of the wires, obtaining in this form information at real time. The foreseen experimental campaigns ( tension tests on straight wires and strands and bending tests on post-tensioned and grouted tendons in concrete beams) will be included in the paper as well as the results and conclusions derived from them.