Structural health monitoring of concrete elements with embedded arrays of optical fibers

Abstract

An optical-fiber sensor system for structural health monitoring of concrete elements such as beams and columns is presented. The system employs arrays of conventional optical fibers embedded in the concrete elements as crack sensors. Twelve types of optical fibers as well as several embedding techniques have been tested for this role. The survival rate of optical fibers embedded in concrete could be as high as 80%. The loss of fibers during the embedding process was acceptable provided that the number of fibers in the array had redundancy. The optical transmission of all fibers in the array was monitored in a time-division multiplexed mode at a high repetition rate, in the kHz range. The monitoring scheme allowed a quasi-continuous data acquisitions of large optical fiber arrays. A sharp decrease in the optical transmission of one or more optical fibers was a clear indicator of the development of cracking in the element subjected to flexural loads. The system was successful in detecting not only the initiation but also the propagation of cracks in concrete elements subjected to incremental flexural loading. In this work, the relation between the mechanical properties of the optical fibers and their behavior for the described application is discussed. Also, considerations towards a rational design of the system are proposed. The damage detection system may be used for the mapping and monitoring of cracks in concrete elements. The simplicity of the operation and relatively low cost of the proposed system make it a great candidate for applications in structural health monitoring of critical elements in civil infrastructure.