Engineers to Conduct Fracture Test on 120-Foot Bridge Using Explosives

Event: Structural engineers at the Ferguson Structural Engineering Laboratory at The University of Texas at Austin will test the stability of a full-sized bridge in the event of a complete fracture of a steel girder.

When: 3 p.m., Friday, June 6. The actual test will last less than a minute. Media should arrive no later than 1:30 p.m. Press briefings and viewing of the test bridge will be available from noon-2 p.m. Media access to the test site after the detonation will depend on the condition of the structure and safety precautions.

Media credentials will be required to enter the J. J. Pickle Research Campus from the Braker Lane or Burnet Road entrances. Media can notify entrance gate security of their purpose to view the bridge test at Ferguson Lab.

Where: The storage area south of the office building of the Ferguson Structural Engineering Laboratory. A map of the campus is online. A live webcast begins at 2:30 p.m.

Background: The test is part of a research project to determine the collapse vulnerability of twin box girder bridges in the event of a complete fracture of one of the twin girders. Structural engineers consider these bridges "fracture critical" because they are expected to collapse if their girders fracture. The test team is led by Karl Frank, professor of structural engineering, and Eric Williamson, associate professor of structural engineering. The team is developing analytical methods to determine the vulnerability of these bridges. The full size test of this instrumented bridge will provide valuable data to calibrate their analytical models.

Twin box girder bridges are often used in freeway interchanges when long, curved spans are required such as the one at the Interstate 35 and Highway 290 interchange in Austin. About two years ago, the laboratory's test bridge, which was removed from the interchange of Interstate 10 and Loop 610 in Houston, was tested to see the effects of a brittle fracture in a girder. This time, the testing is for a full-size fracture, making it likely that the girder will experience substantial displacement, Frank says.

The weakened 120-foot-long girder is one of two girders supporting the concrete deck and a 73,000-pound truck. One of the girders will be supported by a jack system because its flange (the bottom plate of the girder) and its webs (the girder's vertical plates) will have been cut. About 200 grams of explosives will be used to sever the tension ties in the jacks supporting the test bridge.

Once the explosives sever the ties, the bridge's weight and the simulated truck load will be transferred from the fractured girder to the intact girder through the concrete deck. More than 200 gauges and displacement transducers will record how the bridge reacts to this extremely damaged condition. The data will be used to develop analytical methods that engineers can apply to assess the behavior of the many box girder bridges in the state's transportation system.

The Texas Department of Transportation and the Federal Highway Administration are funding the research.