Bridge Researchers Get Valuable Lesson in Structural Failure

by Diane S. Kukich

October 1, 2003

A research team from the University of Delaware Center for Innovative Bridge Engineering (CIBrE) had an unprecedented opportunity earlier this week to test an undeteriorated bridge to failure. Owned by the Delaware River and Bay Authority, the bridge was in good condition but was being eliminated as the result of improvements to the traffic patterns near the Delaware Memorial Bridge.

According to CIBrE Director Dr. Dennis Mertz, Professor of Civil and Environmental Engineering, the team's goal was to learn about the post-yield behavior of the three-span bridge, a common type consisting of a concrete deck on steel stringers. "Because the bridge was being demolished anyway, we had the chance to load it beyond the point where it could be loaded and then salvaged," Mertz said. Coordinated by research technician Gary Wenczel, the bridge was instrumented with nearly 100 sensors to provide feedback about the structure's behavior during and after loading.

Although graduate students Adrienne Johnston, Peter Quinn, and Julia West had high hopes that the bridge would fail catastrophically, it remained standing with little damage evident after almost 2 million pounds of asphalt shavings—the equivalent of some 20 dump trucks stacked upon each other—had been piled on a small section of the bridge. But Dr. Michael Chajes, Chair of CEE and a Bridge Center affiliated researcher, was not as disappointed in the results as the students were.

"What this tells us is that bridges are much stronger than we might think they are," he said. "In addition to the normal wear that the bridge had already sustained through daily use, we deliberately induced more damage by cutting away a portion of the flange of each member. Despite that, the bridge was still able to carry significantly more load than it would ever have to bear with traffic. We're very grateful to DRBA for giving us the opportunity to do this and learn from the experience."

Joe Volk, bridge engineer at DRBA, was as interested in the results as the UD team. "This cost us about $12,000 over and above the cost of the demolition," he said, "but it's worth it because it's great for the bridge community. That's why we're doing it."

Associate Professor Harry "Tripp" Shenton, whose area of expertise is structural health monitoring, was also grateful for the chance to test the bridge. "This was a unique opportunity to test a full-scale structure in a way that we can use the information to validate some of the theories we're developing for damage identification and health monitoring," he said.

According to Chajes, DRBA is planning to eliminate more bridges in the next few years. "We hope that this test will provide insight into the development of more robust plans for testing the additional bridges," he said. "That knowledge, in turn, will contribute to our overall database of information about the design and monitoring of bridges."

Funding for the test was shared by CIBrE and DRBA, and all personnel time was donated.

To read an update on this story, click here.

CEE graduate student Peter Quinn watches as dump trucks are driven across the bridge to help assess its initial condition.

A crane loads the bridge with almost 2 million pounds of asphalt shavings—the equivalent of some 20 dump trucks stacked upon each other.