Detecting Cracks In Steel Bridges Using Fiber Sensors

Jordan Stringfellow Mechanical Engineer Lightwave Division

According to the American Society of Civil Engineers (ASCE) in its 2013 Report Card for America's Infrastructure, one in four bridges in the Unites States are "either structurally deficient or functionally obsolete". It is approximated that $3.6 trillion is needed to improve the United States’ current infrastructure grade of D+ to an average grade of B. Infrastructure management teams require more detailed information about structural performance, yet current rating systems rely heavily on visual inspections, which can be highly variable and lead to inaccurate assessments. In a paper published by members of ASCE in the Journal of Engineering Mechanics, distributed fiber optic strain sensors were used to monitor and identify simulated cracking and distributed deterioration on steel specimens designed to simulate components of bridges. Strain measurements were taken with a Luna OBR 4600 system. The OBR 4600 is able to provide strain measurements down to a 2 mm spatial resolution for a measurement range of up to 70 m. In this work, it was used to report sensing points every 10mm along fiber optic sensors. These measurements were then compared to foil gages and numerical finite-element models of the specimens, showing excellent correlation as evidenced in the figure below.

The paper reports that fiber optic sensors can be used to accurately detect cracking and measure changing strain fields in steel structures. The ability to use these sensors to localize and detect deterioration of critical bridge components can help address some of the safety concerns we face with our current deficient bridge infrastructure. The full paper is available from the ASCE Library and can be accessed online here. For more information about Luna’s fiber sensing solutions visit the Sensing section of our website. *** Publication Reference: Hoult, N., Ekim, O., and Regier, R. (2014). Damage/Deterioration Detection for Steel Structures Using Distributed Fiber Optic Strain Sensors. J. Eng. Mech., 140(12), 04014097. Top image: “Portland Oregon steel bridge panorama" by Matthew Field. Licensed under GFDL 1.2 via Wikimedia Commons