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Engineering design work focuses on improving quality of bridges

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As the United States struggles to pay for expanding and maintaining the nation's transportation infrastructure, a University of Houston research team is proposing changes to the design for bridge construction that could dramatically lower maintenance costs while improving the quality of the bridges.

Yi-Lung Mo, professor of civil and environmental engineering, is principal investigator for more than $1.2 million in grants from the Texas Department of Transportation (TxDOT) to consider new solutions to two structural problems.

A report released last week by the American Road and Transportation Builders Association reported that nearly 10 percent of U.S. bridges were considered structurally deficient last year.

Mo's most recent TxDOT funding comes in two grants: $623,595 to redesign the way steel reinforcing bars – or rebar – are positioned inside concrete bridge caps, and an additional $616,995 to determine how best to connect the bridge column with the embedded drilled shaft.

Mo, whose research is focused on improving the safety and reliability of infrastructure and building materials, said his proposal would improve the way a style of bridge cap – used to support the girders underlying a bridge – is reinforced. Traditional bridge caps are rectangular, making it easy to evenly space the rebar in a grid.

But about 30 percent of the 50,000 bridges maintained by TxDOT are on curving landforms, which require that the bridge bent cap instead be a parallelogram, or skew, Mo said. Because the corners don't form right angles, the rebar can't be evenly spaced there, resulting in it being too widely spaced on one side and too closely bunched on the other.

That uneven spacing makes the cap more likely to crack, driving up maintenance costs. Mo proposed a novel way to uniformly distribute the rebar throughout the entire skewed bent cap. He said that's never been tried but that computer modeling suggests reduced costs for design, construction and maintenance will be about 30 times greater than the cost of the research.

After additional computer modeling, Mo will build a full-scale bent cap specimen – about 24 feet-by-5 feet – and test it in the University's Thomas Hsu Structural Research Laboratory. Testing will involve using a load of one million pounds to determine the load deformation relationship, he said.

Under the second grant, Mo has proposed a way to better stabilize the bridge column connection to the drilled shaft – an element of the foundation, with a round hole drilled into the ground, reinforced with steel and then filled with concrete. Both components are reinforced with steel. But because the shapes don't align exactly and rebar is most effective along the outer edges of the shaft and column, Mo said that one piece of rebar can't be used for both components.

Linking the two with dowel bars embedded in the concrete would achieve that, but because of the design, the bars can't establish contact with the rebar in both components. Mo, relying on computer simulation, has proposed a way to stabilize the components even without contact. As with the bent cap work, the new design will ultimately be tested in the Thomas Hsu Structural Research Laboratory.

His two latest grants bring Mo's total funding from TxDOT to $4.7 million.

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