Short-Term Evaluation of a Bridge Cable Using Acoustic Emission Sensors

About the report:

The Varina-Enon Bridge carries I-295 across the James River and crosses over the shipping channel that leads to the Richmond (Virginia) Marine Terminal.  The bridge is a cable-stayed bridge that was opened to traffic in July 1990.  It has 150 ft of vertical navigational clearance and 630 ft of horizontal navigational clearance.  The overall bridge length is 4,686 ft.  The bridge has six lanes (three each way) with full right and left shoulders.

This study used acoustic emission (AE) to assess the condition of strands by examining for active defects (such as corrosion, crack expansion and rubbing, wire breaks, and similar active defects) on a single stay-cable, from anchorage point to anchorage point, of the Varina-Enon Bridge.  Testing was performed over short durations of time during periods that included low traffic volumes (acoustically quiet) and high traffic volumes (acoustically noisy).  In addition, computer software was used to determine the source and location of the acoustic event.  The most significant finding was that AE events were being generated inside the pylon in the saddle region.  Further, although AE responses from the stay-cable did not contain any signatures of rubbing from previously broken cable and/or breaking during the testing period, AE signals were detected, possibly because of higher winds or blowing debris striking the cable/anchorage region. 

The study recommends that the Virginia Department of Transportation’s Richmond District Bridge Division measure and map the cracks in the northern and southern stay-cable pylons of the bridge; evaluate the northern pylon saddle regions using AE and determine which areas show the greatest acoustical activity; evaluate the stay-cable anchorage regions more closely using AE; and determine the source of the AE signal that was detected during this study.  Finally, the anchorage regions should be evaluated, and VDOT should consider using AE periodically to evaluate the health of this structure and determine which regions are exhibiting significant AE activity.  Regions with elevated AE activity should take precedence over non-active regions during inspection.

Authors