Unlike ancient bridge builders, who used walls and roofs to keep underlying structures from rotting and rusting, today’s engineers are working on ways to protect bridges from terrorists. “Government officials have acknowledged the transportation system’s vulnerability to terrorist attacks. Bridges are among the most vulnerable,” according to an announcement from the University of Missouri College of Engineering.

Sam Kiger and Hani Salim, the College of Engineering’s associate dean for research and assistant professor of civil engineering, respectively, are working on designing a protective wall capable of withstanding an explosion. “They are collaborating with the U.S. Department of Transportation which provided $85,000 for the research.”

“The wall will shield a bridge’s crucial areas, such as its pier and towers. Ideally, it would be easy to add to existing bridges, and just as easy to remove, if wanted,” said Kiger. “The technology will also be incorporated into new construction,” according to the announcement.

“The research team is examining materials to determine the combination of strength and flexibility necessary to protect bridges from a blast and resulting debris from the wall. This month, two high explosive tests will be conducted in cooperation with the U.S. Army Engineer Research and Development Center and Federal Highway Administration researchers.”

To control costs, research will focus on using concrete and steel, which are materials bridge-engineers are familiar with,” Kiger said. “We’re trying to figure out the most practical way to do this.”

“A blast would destroy the protective wall, but the bridge will be safe because the wall will block most of the blast’s shockwaves,” Salim in the announcement.

After the research is completed, the team will offer it to transportation officials across the country.

Kiger and Salim’s research complements work done by Michel Bruneau, a professor in the Department of Civil, Structural and Environmental Engineering in the School of Engineering and Applied Sciences at the University of Buffalo. His “bridge-pier design uses corrosion-resistant steel tubes filled with concrete, but without reinforcing bars. The steel [tube surface] and concrete bind together, forming a composite structure that gives the piers superior strength and ductility – meaning the piers will bend without breaking when subjected to blast . . . forces,” according to The University of Buffalo Reporter. “For the bridge pier’s footing, additional structural shapes are embedded in concrete to resist the large flexural (bending) forces developing at the based of the bridge piers,” the university publication added.

Unfortunately, these special design features are intended only for small- and medium-sized bridges, but they could serve well, nonetheless. Terrorists may not achieve the same symbolic satisfaction taking down one of these smaller bridges as they would a monumental bridge (think Golden Gate, Verrazano-Narrows or Brooklyn bridges), “but if their objective is to disturb the economy, they have more access to these bridges than the monumental bridges,” said Bruneau in The University of Buffalo Reporter, according to Dellacontrada.

To ensure Bruneau’s designs would prevent catastrophic failure, the U.S. Army Corps of Engineers Research facility in Vicksburg, Miss., was used for testing. “One-quarter scale prototypes of Bruneau’s bridge piers were subjected to blast forces similar to what would occur if someone packed their trunk with explosives and tried to blow up a bridge,” Bruneau said. “Permanent bends, but no significant damage, were experienced by the bridge piers as a result of the blasts.”

Among the 600,000 bridges in the United States, preliminary studies indicate that there are approximately 1,000 where substantial casualties, economic disruption, and other societal ramifications would result from isolated attacks. The estimate of 1,000 critical bridges is based on information presented in the National Needs Assessment for Ensuring Transportation, Infrastructure Security: Preliminary Estimate, NCHRP Project 20-59(5), prepared by Parsons Brinckerhoff and SAIC, June 2002, and published in the Recommendations for Bridge and Tunnel Safety report from The Blue Ribbon Panel (BRP) on Bridge and Tunnel Security.

“Although past attempts at quantifying the total cost of a bridge or tunnel outage from natural disasters have not yielded widely accepted results, the BRP believes that loss of a critical bridge or tunnel could exceed $10 billion,” explains the report. “Countermeasures considered in response to potential threats and damage was a key element when the BRP established a framework during its initial meeting for addressing bridge and tunnel security.”

Clearly, the bridge protection technologies developed in the colleges of engineering fit into the category of countermeasure.

Resources

MU Engineering Researchers Designing Protective Wall to Shield Bridges from Terrorist Attacks
University of Missouri, June 5, 2007

New bridge design protects against terrorist attacks
by John Dellacontrada
University of Buffalo Reporter, Jan. 26, 2006

FHWA Recommendations for Bridge and Tunnel Safety
by The Blue Ribbon Panel on Bridge and Tunnel Security
Federal Highway Administration, September 2003