Simulations of 9/11 crashes could assist building designs.

• Author: Venere, Emil

Engineers, computer scientists and graphics technology experts at Purdue University, in West Lafayette, Ind., have created a simulation that uses scientific principles to study in detail what happened when a Boeing 757 crashed into the Pentagon last year.

Researchers said the simulation could be used as a tool for designing critical buildings--such as hospitals and fire stations--to withstand terrorist attacks.

The simulation merges a realistic image of the airliner approaching the building with a technical, science-based animation of the plane crashing into the structure.

"This is going to be a tremendous asset," said Mete Sozen, professor of structural engineering at Purdue. "Eventually, I hope this will be expanded into a model that we can use to help design structures to resist severe impact loads.

"Using this simulation, I can do the so-called 'what-if' study, testing hypothetical scenarios before actually building a structure."

The simulation can be recorded on a DVD and played on an ordinary personal computer.

The software tool is unusual, because it uses principles of physics to simulate how a plane's huge mass of fuel and cargo impacts a building. The plane's structure caused relatively little damage, and the explosion and fire that resulted from the crash also are not likely to have been dominant factors in the disaster, Sozen said.

The model indicates the most critical effects were from the mass moving at high velocity.

"At that speed, the plane itself is like a sausage skin," Sozen said. "It doesn't have much strength and virtually crumbles on impact."

But the combined mass of everything inside the plane--particularly the large amount of fuel onboard--can be likened to a huge river crashing into the building.

The simulation deals specifically with steel-reinforced concrete buildings, as opposed to skyscrapers like the World Trade Center's twin towers, in which structural steel provided the required strength and stiffness.

Reinforced concrete is inherently fire resistant, unlike structural steel, which is vulnerable to fire and must undergo special fireproofing.

"Because the structural skeleton of the Pentagon had a high level of roughness, it was able to absorb much of the kinetic energy from the impact," said Christoph M. Hoffmann, a computer sciences professor at Purdue's Computing Research Institute.

Sozen created a mathematical model of reinforced concrete columns. The model was used then as a starting point to produce the...