After completing a series of explosions at nearby Fort Leonard Wood, Mo., researchers at the University of Missouri-Rolla say they are still confident their retrofitting techniques could improve a bridge’s ability to withstand everything from blasts to earthquakes to old age.
Dr. Genda Chen, professor of civil, architectural and environmental engineering and interim director of the Center for Infrastructure Engineering Studies, and Brian Wood of Rolla, a graduate student in civil engineering, designed and constructed three identical, one-quarter-scale replicas of typical bridge columns — with one exception. Inside each of the columns was a sensor that could find cracks and other damage not seen during visual inspection, Chen says.
“The problem with visual inspections is that much of this damage in columns can’t be seen after the earthquake or disaster is over,” Chen explains. “Cracks on the columns are typically closed immediately after an earthquake due to gravity loads. You won’t be able to see them with your eyes — but this sensor can pick them up.”
Of the three 10-foot columns, one remained bare to serve as the benchmark; a second was strengthened with a sheet of carbon fiber-reinforced polymer; and a third was reinforced with carbon FRP and then coated with a rubber-like layer before being covered with an additional FRP sheet.
“The FRP sheet is used to confine concrete,” Chen explains. “We used the rubber-like material to dampen or modulate the shockwave effect.”
Chen and Wood worked with UMR explosives expert Dr. Jason Baird to initiate four explosions using increasing levels of high explosives.
“FRP composites have very high strength-to-weight ratios in addition to being resistant to corrosion and fairly easy to apply,” Wood says. “They are already used in bridge strengthening, but the additional rubber-like layer increases the amount of energy that is dissipated during an extreme loading situation such as an earthquake or an explosion, which can significantly decrease the risk of a catastrophic failure.”
The FRP performed better than expected during the explosions, considering the close proximity of the blast to the columns, Wood says.
“We would like to do some additional blast testing on replica bridge columns strengthened using this methodology,” Wood says.
Chen credits the strong support from Fort Leonard Wood as being the key to the smooth operation and success of this series of tests.
Want to watch? Click here to watch a few of the explosions (WMV).