Engineers face challenge of bomb-resistant design

The videos detailed the engineering dilemma – slow-motion shots of the inside of an office after a bomb went off outside a window.

In the first experiment, the blast shattered the standard glass, hurling thousands of razor-sharp shards head high into the room.

In a second test, where the glass was sandwiched around a thick layer of clear plastic for reinforcement, there were no shards. There was no protection either.

The plastic-clad window caved inward with the blast, pulled out of its metal frame and hurtled intact across the room, slamming lethally into the head of a test dummy.

This week, about 100 engineers and architects from around the world are gathered at the Sheraton Norfolk Waterside Hotel to try to learn how to protect people when their buildings are attacked by terrorists.

What was once the province of only the military has increasingly become a civilian concern.

It’s a difficult science, as the two videos showed. Simply strengthening one aspect of a building may have disastrous results. Put a rigid bar into the wall to reinforce a window, for example, and it could turn into a projectile instead. But stretch out that bar a bit, make it a little more flexible, anchor it a little better, and it could make a life-and-death difference.

The military has long known how to make things bombproof . It developed the science as it built ammunition depots and battleships. Much of the early civil defense work revolved around nuclear attacks and fallout shelters.

But the effort began to shift toward commercial buildings when terrorists attacked the Marine barracks in Beirut, Lebanon, in 1983, killing 241 servicemen, and the Khobar Towers military housing complex in Saudi Arabia in 1996 , claim ing 19 American lives.

It struck home when a fertilizer-and-fuel-oil filled truck was detonated, destroying the Alfred P. Murrah Building in Oklahoma City in 1995, killing 168 .

And then the commercial demand took off on Sept. 11, 2001, when the World Trade Center towers and the Pentagon were attacked and nearly 3,000 were killed, officially launching America’s war on terrorism.

Much of the research was already in place, performed by the British after decades of dealing with Irish Republican Army attacks. Other information came out of efforts to deal with the power of hurricanes, especially Andrew in 1992 .

Research, though, showed that assumptions were often wrong. For instance, if the windows are made of tempered glass, like those in a car windshield, people figured it would be safer because the glass would shatter into little chunks under stress.

That turned out to be true, but only to a point. Those chunks clumped together after a bombing, ending up in shards the same size and with the same lethality as regular window glass, tests showed.

“What we try to do as engineers is to limit the catastrophe,” said Bernie J. Deneke, a special assistant with the Naval Facilities Engineering Command in Norfolk, who works on protecting sailors and who helped set up the conference. “We want to limit the amount of damage and limit the fatalities.”

The conference was sponsored by the Norfolk branch of the American Society of Civil Engineers and the Tidewater Chapter of the Virginia Society of Professional Engineers .

Deneke has seen the need firsthand. He responded with emergency workers to the Pentagon after Sept. 11 and to the federal building in Oklahoma City.

Engineers have a lot more tools these days, he said. New software can help them design buildings to keep them from collapsing as they did in Oklahoma City and at the World Trade Center.

Windows and frames are available that will absorb blasts. Special lacy curtains are available that will catch shards before they get into a room.

There are even blast-proof windows that can be opened to let in a breeze, but close tight for protection under the force of a bomb.

Nobody wants to work in concrete, windowless bunkers, Deneke said. That leaves it to engineers and architects to find ways to compensate.

“We’re trying to strike a balance,” Deneke said.

600450 Engineers face challenge of bomb-resistant design
Date: 10 June 2004

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