Engineering grad students get SMASHed
LOGAN — With a piece of a former 4500 South bridge support from eastside I-215, Dave Petty and Parry Osborn, aided with a computer, began applying pressure.
At 140,000 pounds, the bridge piece began to pop and crack.
At 250,000 pounds, the sounds turned to thuds, and small pieces of concrete began to fly.
At 380,000 pounds, long cracks — technically called "shear failures" — appeared on both sides. Petty and Osborn, graduate students in civil engineering at Utah State University, turned off the pressure.
The test was complete.
The conclusion: Utah Department of Transportation bridge girders — the support pieces of a bridge — are 27 percent stronger when reinforced with carbon fiber.
On Monday, Petty and Osborn tested, for the eighth and final time, a girder that had been part of a freeway bridge. The test was conducted with other graduate civil engineering students in Marvin Halling's course titled Civil Engineering 6050: Experimental Methods. Dismissed from class, they were assigned to calculate and compare reinforced bridges and non-reinforced bridges under pressure.
Petty and Osborn have also tested non-reinforced girders from the 4500 South bridge and concluded that a girder of the same size without carbon fiber would get shear failures at about 300,000 pounds.
"What we're looking at are extreme cases," said civil engineering professor Paul Barr, who also works in the new Systems Materials and Structural Health lab in which the 4500 South bridge was tested. "When does it actually fail?"
UDOT passed the old girders to USU's SMASH lab and challenged students and faculty to test the girders' strength. They also challenged USU to find other materials or methods to make existing bridges stronger, which would be cheaper than building new bridge.
Petty and Osborn discovered carbon fiber when researching bridges in other locations, such as California and Nevada. "We got some of our research from Canada," Petty said.
Carbon fiber is known for its strength and has been used in aerospace and military. "Carbon fiber is in the hull of the Navy's new war ship," Osborn said.
It would be too expensive to construct girders completely out of carbon fiber. But attaching it to the sides of girders or in weak spots on the bottoms of girders is cost-effective. The carbon fiber that the Salt Lake City offices of BASF Global donated to USU for the project normally costs about $20,000.
The testing has cost about $200,000, paid for with state and federal funds. Petty and Osborn will submit a paper to UDOT with their calculations and conclusions in coming months. They graduate in May.
In Salt Lake City, Carmen Swanwick, UDOT chief structural engineer, is excited to read the results. UDOT has used carbon fiber in bridges that have been struck by vehicles.
UDOT engineers want to learn additional techniques and ways to use carbon fiber.
"We're looking at ways to implement the carbon fiber wrap," she said.
e-mail: lhancock@desnews.com
