Bridge sensing using a fiber Bragg grating quasi-distributed transducer: in-field results

Abstract

Structural health and behavior monitoring have always been both a common concern and need in civil engineering. Several classical approaches have been given to this problem including the widley used strain gauges as well as the topographic measurements. These two techniques are almost always used to monitor the behavior of the structures whereas the health monitoring is accomplished by a simple periodic visual inspection. These approaches present serious problems that limit their practical use in real structures such as: lack of fiability, long-term drift, impossibility of full-time measurements, or lack of thoroughness. Centering the discussion in the strain gauges, for being the most representative of the classical civil engineering monitoring methods, it must be said that due to their electric nature they are exposed to both electromagnetic interference and corrosion. The latter greatly reduces their operating life time pushing it typically to less than one year after installation. That is whey new ways of monitoring civil structures were looked for, and that is how photonic fiber sensing came up. Characteristics shared by all fiber senors are their electromagnetic immunity for being manufactured using a dielectric material, low weight, small size, and compatibility with construction materials. As can be seen these inherent characteristics make them very suitable for their use in civil engineering structures. An example of a quasi-distributed transducer is presented in this communication. First the theoretical fundamentals of the transducer and its behavior is explained, and an in-field experiment consisting on monitoring a bridge is described and its results reported.