UCSD Jacobs School of Engineering University of California San Diego
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Protecting Buildings from Bomb Blasts

JACOBS SCHOOL STRUCTURAL ENGINEERS originally developed composite overlays to protect buildings efficiently from earthquakes. The material is about as thin as a cotton shirt, and is made up of carbon threads woven to increase the strength and flexibility of a structure. This prefabricated material is applied like wallpaper to walls, floors or columns. The composite overlays allow the building to absorb horizontal forces and prevent key structural components from cracking and causing the building to fail. Some 2,000 hospitals, parking garages and commercial and residential buildings worldwide have been retrofitted using the technique.

“We see this as a real opportunity to make a difference to help save lives,” says Gil Hegemier, Professor of Structural Engineering, who along with Structural Engineering Professor and Jacobs School Associate Dean Frieder Seible, is working with industry partners and the government on research to safeguard buildings against blast loads.

Hegemier says that after the bombing of the Oklahoma City federal building in 1995, he began thinking about the similarities between earthquakes and blast loads. “In Oklahoma, three of the five ground floor columns collapsed, the load on those columns could not be redistributed, and then the first floor fell in. Finally, the entire building collapsed on itself in pancake fashion. We’ve seen this same kind of failure over and over again when we’ve visited sites damaged by major earthquakes.” Karagozian & Case (K&C) went on to create a computer simulation of the blast on the building, and predicted that had the building been retrofitted with composite overlays, it may have withstood the catastrophic collapse.

In 1998, these compelling predictions resulted in a research and development contract from the Defense Threat Reduction Agency (DTRA) to investigate measures to retrofit U.S. Embassies and other critical structures worldwide against blast loads. One of the first tests was a full-scale blast test on a four-story building at the White Sands Missile Range in New Mexico. The testbed reinforced concrete building is typical of embassies and of low-rise office facilities on the East Coast. Without the retrofit technique, first floor columns in the building were basically destroyed by a blast from C-4 explosives.

Before Retrofit
After Retrofit

But when the columns were rebuilt and retrofitted with carbon overlays, the same bomb caused little structural damage.

The UCSD team continues tests at White Sands, but is concentrating on design equations and methodologies to optimize blast retrofit. They have created a second testing site at the Kirkland Air Force Base near Albuquerque, New Mexico where they can confirm their theories by conducting blast tests on full-scale building components.

Ironically Professors Seible and Hegemier were preparing for a blast test at Kirkland on the morning of September 11 and the base was closed off due to the infamous terrorist attack.

“Clearly, our retrofit technology was developed to protect against blast loads and would not have saved the World Trade Center,” says Seible, who explains that the collapse of the towers was caused when jet fuel from the airplane burned at extremely high temperatures and melted the steel structure. “However, we are developing systems for new construction which may also offer further protection to highrise buildings.”