Pilot Study on Rugged Fiber Optic Brillouin Sensors for Large-Strain Measurements to Ensure the Safety of Transportation Structures

Brillouin-scattering Optical Time Domain Reflectometry (BOTDR) is a viable technology for simultaneous, distributed strain and temperature measurements for miles-long transportation structures. It is a promising tool to ensure the smooth operation and safety of bridge structures that are key links in surface transportation networks or between various transportation modes: i.e., from airport to train station. Currently, telecom-grade optical fibers are widely used in civil engineering for strain and temperature measurements. These fibers are very fragile and easy to break during installation and measurement. In order to understand the ultimate behavior of structures, more rugged optical fibers such as carbon/polyimide coated fibers were recently proposed. One laboratory study on two single fibers indicated that new carbon/polyimide coated fibers can sustain a maximum strain of up to 4%, which can survive any local crack in concrete members or buckling in steel members once they are installed on the structural members. This project aimed to characterize the ruggedness and signal loss of various packaged optical fibers and validate their performance as sensors. Among the tested optical fibers, bare single-mode fibers (SMF-28) with uncoated anchoring have the lowest shear strength and the lowest ultimate strain under tension, and are thus not suitable to apply in harsh environments. Polyimide-coated optical fibers have the highest shear strength and the highest ultimate strain under tension, making them the best candidate for civil infrastructure applications. Both glass fiber reinforcing polymer (GFRP) and carbon coated optical fibers are sufficiently rugged to be applied to civil infrastructure