The National Cooperative Highway Research Program awarded Gary Prinz, associate professor of civil engineering at the U of A, $800,000 to study the design of shear pin connectors in composite steel bridges.
Bolt shear connectors are used to provide shear transfer between the concrete slabs of the bridge and the steel girders. They are typically welded to the top of the steel beam.
The aim of the four-year grant is to determine how loads are transferred from the concrete to the steel via the shear force anchors. Of particular interest will be investigating the strength and fatigue limits of connectors in hopes of aiding more efficient design. More efficiently designed bridges generally mean cheaper bridges – or more bridges for the money.
“We generally assume that all of the load goes directly through this small bolt and that no other forces are transmitted through friction or adhesion between the concrete and steel,” Prinz said. “In our project, we therefore have the task of precisely determining the interaction of the different loads and quantifying the different load paths that can occur.”
Much of the work is done at the Grady E. Harvell Civil Engineering Research and Education Center, of which Prince is the director. He will build 60-foot long bridge sections for large-scale fatigue testing. In total, he anticipates five large-scale tests and numerous smaller component-level tests.
“The measurement problem we face here,” explained Prinz, “is trying to understand how much load goes through something embedded in concrete. And the tricky part is that the loads we’re trying to measure are perpendicular to the direction of the bolts – so we’re trying to measure shear transfer in an element embedded in concrete, and that’s not easy.”
The project also takes Prinz and his team to bridges under construction. Before the slabs are poured, gauges are placed inside them in hopes of recording what is happening during construction and under controlled traffic loads. Minor testing of measurement components is also performed on-site at the Harvell Center.
Prince emphasized that this is also a great opportunity for graduate student Callie Clark, who is completing her Ph.D. are working with Prinz on the project, which will include welding, concreting, designing test fixtures for measurement components, creating load programs and conducting tests.
Ultimately, Prinz believes that meeting the terms of the grant will likely contribute to federal bridge design standards, with potential consequences for the design of any future composite steel bridge.
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