A group of UMR researchers led by Genda Chen has developed a way to retrofit bridges to help them withstand everything from blasts to earthquakes to old age.
Last summer, the researchers completed a series of explosives tests on their retrofitted bridge components at Fort Leonard Wood, Mo. The initial results make the researchers confident that their technique will improve bridges’ ability to hold up under pressure.
Chen, a professor of civil, architectural and environmental engineering and interim director of the Center for Infrastructure Engineering Studies, and civil engineering graduate student Brian Wood 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 (FRP), and a third was reinforced with carbon FRP and 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 Jason Baird, PhD MinE’01, 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.”