http://www.wai.com/AppliedScience/Blast/blast-okcity.html
BY JOHN PRENDERGAST(Reprinted by permission from Civil Engineering, October 1995)
Can lessons learned from the tragic bombing in Oklahoma City help engineers outwit future terrorists? A key issue in the emerging debate is whether to require that government buildings be designed to protect against progressive collapse.
The explosion that ripped through the Alfred P. Murrah Federal Building in Oklahoma City shortly after 9 a.m. on April 19 killed 168 people, injured more than 500 and damaged more than 300 buildings. Also among the casualties of the blast was a lingering American faith that terrorism was something that happened somewhere else-in other countries, or at high-profile structures like the World Trade Center in New York.
......According to Rittenhouse, "The biggest structural engineering lesson learned from the Oklahoma City bombing was the need to improve the structure's ability to sustain significant local damage and remain standing." It has been estimated that at least 80% of the deaths at the Murrah Building were caused by the structure falling on occupants who might otherwise have survived the bomb attack, he says. "Therefore, the single most important improvement, aside from maintaining a substantial keep-out distance, would be to mitigate catastrophic failure or progressive collapse. This measure alone, regardless of improvements to the glazing and facade, will significantly reduce the number of fatalities." ............................................
Rittenhouse predicts there will be a "significant reduction" in transfer girders in future construction, especially in potentially dangerous locations. The Murrah Building had a transfer girder running across the face of the structure at the second floor, which transferred the weight of 10 building columns to five columns down to the ground. The failure of one column meant three failed; with the failure of two, six or seven failed, he says. "A certain number of people will be looking out a window or standing in the wrong place when a bomb goes off, but the remaining people get crushed," says Rittenhouse. "That's why this is an important issue. You'll have localized damage no matter what, but preventing progressive collapse will limit damage after that."