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A giant hydraulic piston pumps up and down on a long steel bridge beam, subjecting the girder to two million cycles of stress—the equivalent of a bus or truck driving across it every couple of seconds for days on end.
The scene is a massive structures lab in USC’s Department of Civil and Environmental Engineering where researchers are helping the S.C. Department of Transportation (SCDOT) to assess a new type of steel used in bridge girders. South Carolina is among the first states to try the new high-strength, low-carbon beams, which are more expensive than regular steel but stronger and more corrosion resistant.
The beams don’t require painting and are somewhat smaller because of their higher strength, allowing more clearance at a bridge underpass.
“We’re working together with the SCDOT to identify if the use of the high-performance steel in bridge girders is more economical in the long run and then develop guidelines on how the new material should be adopted,” said Dimitris Rizos, an assistant professor heading a team of engineers on the project, which is funded by the Federal Highway Administration and SCDOT.
As part of the strength and fatigue testing, the bridge beam in USC’s lab is outfitted with sensors that measure even the slightest deformations while the beam is pressed down by the piston. Sensitive acoustical sensors detect slight changes in intensity of acoustic emissions as the beam bends up and down—the nearly imperceptible noises are related to the normal formation of micro-cracks in the steel.
“When the first bridge with these beams is built on Hwy. 29 near Greenville, we’ll set up sensors there to monitor in real time how the steel is performing under service load conditions,” Rizos said. “Next summer and again in the winter, we’ll also perform controlled tests by parking loaded sand trucks on the bridge and correlating loading with girder deformations.”
The laboratory and field testing are necessary steps before South Carolina makes a full commitment to adopting the new material for bridge construction and replacement across the state.
Rizos is working with fellow assistant professors Paul Ziehl and Juan Caicedo on a number of projects related to bridge engineering, including, but not limited to, corrosion resistance studies of steel reinforcement, fiber-reinforced polymers for bridge rehabilitation, seismic response and assessment of bridges, and health monitoring.
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