SLUG: 7-37272 World Trade Center Structure
TYPE=English Programs Feature
TITLE= World Trade Center Structure
ATTENTION: WORLD TRADE CENTER BUILDING STRUCTURE
INTRO: The twin towers of the World Trade Center were believed to be structurally safe, and had survived a car bomb attack in 1993. So why did they collapse? As Rosanne Skirble reports, it was the intense heat from the fire that broke out after the two jet airliners flew into the buildings that turned them into rubble.
TEXT: The twin towers of the World Trade Center were designed to withstand the wind force of a hurricane, even the impact of a jet plane. That's what Gerry Schwartz says. He's the incoming President of the American Society of Civil Engineers.
TAPE CUT ONE: GERRY SCHWARTZ
"The first impact (of the planes) did not bring the towers down, and that in a way is a tribute to the structural integrity of the building."
TEXT: The structure supported by a skeleton of steel columns was considered innovative when it was completed in 1973, but is now a common design for skyscrapers.
The tube-like towers had sixty-one steel columns coated with insulation on each side and a cluster of steel columns, also coated with insulation, in the center to hold up the stairs and elevators. A network of tresses or beams ran between the groups of columns to support the concrete floors. And, placed among the tresses was a special set of plates meant to dampen the stress of winds up to 300 kilometers per hour.
Gerry Schwartz says it was the combined impact of jets filled with fuel, the ensuing explosion and extreme heat - above 800 degrees Celsius that weakened the vertical steel columns until they buckled.
TAPE CUT TWO: GERRY SCHWARTZ/SKIRBLE
SCHWARTZ: "Almost melting, I suppose. And, when that happened, an entire floor, or maybe a set of floors then collapsed with the entire weight of the building above, hundreds of tons undoubtedly coming down on the floor beneath almost like a pile driver. And, it just slammed the columns straight down one after another they crumbled underneath that enormous load."
SKIRBLE: "(It was) like a house of cards."
SCHWARTZ: "A vertical house of cards that came down, but unique that it came down so straight like dominoes falling, but vertically."
SKIRBLE: "Do you think, Mr. Schwartz, that the events in New York will change the way in which buildings are designed and will security be figured into architectural design more than it has already been in the past?"
SCHWARTZ: "There is little doubt that this tragedy will influence the way we design buildings, particularly high rise buildings. Every catastrophe we have ever had has led to better approaches to the design. Whether we can come up with designs that are fail safe in this kind of bomb-like or missile-like attack is speculative."
"I suppose one could say as engineers we can accomplish almost everything. And perhaps we can figure out fire suppression systems that could have handled that fire and kept the structural integrity. We will certainly change the way we design buildings as a result of this tragedy."
TEXT: Gerry Schwartz is the President-elect of the American Society of Civil Engineers, the trade group for civil engineers in the United States. The organization is sending volunteer teams of forensic engineers technical experts who study the details of structural failure to the disaster scenes in New York and Washington.
TAPE CUT FOUR: GERRY SCHWARTZ/SKIRBLE
SCHWARTZ: "So that we can understand exactly what happened and thereby better design buildings in the future."
SKIRBLE: "What lessons can we learn from this tragedy?"
SCHWARTZ: "The obvious, I suppose. In a catastrophic event in a high rise building one needs to protect the rescuers and the people below realizing that the building itself is at risk. I don't believe anybody understood that before this tragedy. So, the approach to even the rescue operations has to be changed. I think that we will certainly be looking at detailed engineering issues, fire suppression in particular in ways to improve the security in a catastrophic event."
TEXT: Gerry Schwartz says no structure could have withstood the World Trade Center assault. Speaking for the American Society of Civil Engineers, he says that engineers will take the unfortunate lessons from the tragedy to do an even better job of designing buildings to protect both the structures and the people who work in them. (SIGNED)
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