The National Academies

NCHRP IDEA 20-30/IDEA 124 [Completed (IDEA)]

Novel Fiber Optic Sensors for Monitoring Bridge Structural Integrity
[ NCHRP 20-30 (NCHRP-IDEA) ]

  Project Data
Staff Responsibility: Dr. Inam Jawed

This project developed a novel sensor system based on fiber optics and Moiré phenomena for measuring dynamic response of highway bridges to assess their structural integrity. Work in the initial phase focused on developing a prototype sensor system. Technical specifications of the proposed fiber optic accelerometer system were established, and a conceptual design of the system was developed. The sensor head consisted of a pair of parallel grating panels, a pendulum, and two pairs of fibers with collimators. A computer simulation was performed to determine optimal trade-off between the sensor’s conflicting dynamic bandwidth and resolution. Based on data obtained, key design parameters including the optical grating pitch and the mass, stiffness, and damping of the pendulum were determined. A special signal processing algorithm was developed to further broaden the dynamic bandwidth and enhance the measurement sensitivity of the accelerometer. An auto-inspection/auto-adjustment procedure was developed to achieve high accuracy and alignment in fabricating the sensor head.  A portable prototype multi-channel accelerometer system was developed that included multiple sensor heads, a low-cost signal box (for sensor interrogation) and a PC (for signal processing).  The system was tested in the laboratory under a variety of dynamic excitations (including earthquakes) and at two highway bridge sites under traffic excitations. These tests demonstrated superior performance of the new fiber optic acceleration system over its conventional electrical counterparts, including (1) total immunity to electromagnetic interference and lightning strikes, (2) a high sensitivity, high accuracy, and a large measuring range with particularly high performance in low frequencies, (3) a small sensor head with a lightweight optical fiber cable facilitating installation on a long-span bridge, (4) robustness against environmental changes, and (5) a very low cost compared to most optical fiber sensors. Such a sensor system can be conveniently installed on highway bridges for real-time structural health monitoring and also for post-event damage assessment and capacity estimation when integrated with a software system developed by the researchers.   The final report will be available from the National Technical Information Service (NTIS # PB2009102139).

The final report for this IDEA project can be found at:

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