Princeton Junction, NJ – February 2008 – MISTRAS Group Inc. has announced that Physical Acoustics Corporation (PAC) is working with Hampton University and the Virginia Transportation Research Council on a new study to monitor the stay cables of a major bridge on Interstate 295 over the James River along the I-95 corridor.
Hampton University, located in Hampton, Va., is leading this study on the short-term evaluation of bridge cables using acoustic-emission sensors provided by PAC. The Research Council the research division of the Virginia Department of Transportation in partnership with the University of Virginia, located in Charlottesville, Va. will oversee the project on this VDOT-owned bridge.

The bridge’s supporting cables contain steel strands with individual wires. The study will determine if the condition of the strands can be assessed by short-term monitoring with acoustic-emission (AE) instrumentation on a single stay cable of the Varina-Enon Bridge during periods of both low traffic volumes (acoustically quiet) and high traffic volumes (acoustically noisy).

Scientists will conduct AE monitoring during high- and low-traffic volumes two times during the year to account for summer and winter temperature extremes. In addition, this study will evaluate signature sounds and/or wire breaks that occurred during test periods.

This study will enhance VDOT’s ability to evaluate the health of this structure and to pinpoint regions that might require more in-depth inspections. It is all part of the overall effort to ensure the continued integrity of the nation’s bridges.

To perform this study, acoustic emission sensors will be strategically attached to a single cable and monitored for two and a half months during the winter and then two and a half months during the summer.

AE, a non-destructive evaluation (NDE) technique, has the potential to eliminate subjectivity in traditional manual (visual) bridge inspections. A critical advantage of AE testing over other NDE techniques is its ability to detect active flaws, making it a principal candidate for real-time flaw characterization and continuous health monitoring of highway bridges. AE technique is based on the principal that each flaw is associated with varying types and levels of deformations that release energy in the form of stress waves whenever a dynamic micro-structural damage, such as crack growth, occurs.