Fiber optic based monitoring system applied to a centenary metallic arch bridge: Design and installation

In the last decade, fiber optic sensors (FOSs) have been increasingly preferred over electrical ones to integrate structural health monitoring systems installed on new bridges. The added value of this sensing technology in appraising the behavior of centenary structures is also unquestionable. In this article the design of an advanced monitoring system based on fiber Bragg gratings (FBGs) and implemented in a XIX century steel arch bridge is reported. Three major requirements had to be attained with its installation. Firstly, welding solutions for attaching strain sensors to the steel surface were not permitted due to its chemical properties; secondly, the monitoring system should provide reliable data concerning the structure’s behavior at least for a decade; thirdly, FOSs retrofitted to the bridge should have a minimum impact in its aesthetics. Techniques and materials adopted in the system installation and protection of sensors and optical components are pointed out. Experimental tests carried out to comprehensively characterize the sensors response are described, and their results discussed. The guidelines considered in the development of the project, system architecture and objectives to accomplish are also presented. Additionally, some characteristic results of the bridge response during the initial monitoring period are shown.