Distributed Strain Measurement in Steel Bridge with Fiber Optic Sensors: Validation through Diagnostic Load Test
Publication: Journal of Performance of Constructed Facilities
Volume 22, Issue 4
Abstract
Fiber optic sensing technologies are emerging as valid alternatives for the health monitoring of civil structures. Distributed sensors based on Brillouin scattering add the unique capability of measuring strain and temperature profiles along optical fibers. Measurement is performed by establishing the correlation between fiber strain and temperature, and the frequency shift of the Brillouin backscattered light induced by a monochromatic light pulse. The technology holds potential for use on large structures and integrated transportation infrastructure. Its effectiveness has been assessed through scaled laboratory experiments, whereas field validation is limited to very few demonstration projects conducted to date. This paper presents a pilot application of Brillouin optical time domain reflectometry to measure strain profiles along the steel girders of a continuous slab-on-girder bridge subjected to diagnostic load testing. One of the exterior continuous girders required heat-straightening after falling during construction due to wind. The significance of applying a distributed measurement technique lies in the potential to assess the global girder response, which would be impractical and uneconomical using discrete measurement techniques. A long sensing circuit was installed onto the web of four girders. The circuit comprises bare optical fiber sensors, and a novel adhesively bonded fiberglass tape with embedded sensing fibers for strain measurement and thermal compensation. The strain profiles were first converted into deflection profiles and validated against discrete deflection measurements performed with a high-precision total station system. Structural assessment based on comparison of the strain profiles with the results of three-dimensional finite-element analysis of the bridge superstructure, and with specification mandated criteria, indicated that the response of the girder under investigation was within the design limits, and did not pose serviceability concerns. Factors that may affect measurement accuracy are finally discussed on the basis of the experimental and numerical results.
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Acknowledgments
The financial support from the Missouri Dept. of Transportation and the Univ. of Missouri-Rolla Univ. Transportation Center on Advanced Materials and NDT Technologies is gratefully acknowledged. Special thanks are due to Leica Geosystems, Inc., Isaberg Rapid, Pirelli Cavi e Sistemi S.p.A., SEAL S.p.A., Yokogawa Corp. of America, Rolla Technical Institute-Machine Technology and Precision Manufacturing, and Strongwell Corp., industry member of the NSF Industry/University Cooperative Research Center “Repair of Buildings and Bridges with Composites” , for providing precious technical and logistic assistance, materials, and equipment.
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Information
Published In
Journal of Performance of Constructed Facilities
Volume 22 • Issue 4 • August 2008
Pages: 264 - 273
Copyright
© 2008 American Society of Civil Engineers.
History
Received: Oct 25, 2007
Accepted: Mar 31, 2008
Published online: Aug 1, 2008
Published in print: Aug 2008
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