When the World Trade Center’s twin towers crumbled, the debate over the tradeoff between saving lives and saving cash during building construction was vaulted to center stage.
Intense heat from burning jet fuel has been blamed for bringing down America’s Gateway to the Free World. Still, the building’s collapse is raising thorny questions for building engineers as they look to design buildings that are affordable but also safe.
One prominent voice in the debate is that of Eugene Corley, a structural engineer and building collapse expert at Skokie-based Construction Technology Laboratories Inc. Corley on Friday began the job of leading the forensic engineering team investigating the Trade Center collapse–a role he also performed after the bombing of Oklahoma’s Murrah Federal Office building on April 19, 1995.
As he did in analyzing the devastation of the Murrah building, “I’ll be trying to see if anything different could have been done” during construction to prevent the collapse of the Trade Center buildings, Corley said in an interview.
In the case of the Murrah building, Corley said, his report concluded that design changes costing a mere 1 to 2 percent of building costs could have saved the lives of as many as 85 percent of the bombing casualties. While most engineers, including Corley, think the Trade Center buildings performed reasonably well in standing up to the initial impact of the plane crashes, they are less sure about the structure’s resistance to fire. It is generally thought that heat from burning jet fuel reached temperatures higher than normal fires, eventually weakening the steel that provided the essential support for the Trade Center structures.
Experts say the 110-story towers were built to stand up in the face of forceful collisions but not to cope with heat produced by 30,000 pounds of aviation fuel, which flooded into the structure’s core from the crashed planes (this sentence as published has been corrected in this text).
And early indications are that at least one of the five smaller buildings in the Trade Center complex suffered “burn-out,” as fire charred the structure, causing it also to collapse, according to Corley.
The smaller buildings in the Trade Center complex, he thinks, may have partially perished under the weight of falling debris from the destroyed towers.
“I have to say the collapse of buildings this size is a little bit surprising,” said James Milke, associate professor of the University of Maryland’s department of fire protection engineering, referring to the Trade Center towers.
Milke, who is chairman of an industry committee looking at structural design for fire conditions, described the steel’s performance as “disappointing” when compared to that of steel columns and beams in other major fires in skyscrapers.
He points to the nation’s two largest previous fires in high-rise offices.
A fire raged for 19 hours on the 22nd floor of the 38-story Meridian Bank Building in Philadelphia in February 1991 and a blaze in May 1988 lasted for 3 1/2 hours in the 62-story First Interstate Bank in Los Angeles.
Neither building came close to collapse, although firefighters were unable to tackle them for some time, he says.
“How was the construction there different from the Trade Center?” Milke asks.
Corley, too, wants answers to such questions but also cautions against comparisons, given the unique nature of the Trade Center collapse.
“Some of the fire protection may have been compromised as debris from above fell,” said Corley. “This is something we are looking at.”
The buildings’ fire protection measures raise important questions.
When the 1,360-foot-tall towers opened in 1973, they were thought to be the first steel structures to use non-asbestos fireproofing, according to the National Council of Structural Engineers Association.
The fibers of the spray-on fireproofing designed to protect the structures’ steel columns were ceramic, rather than the cancer-causing asbestos.
The events of the last few days are also sure to lead to an examination of high-rise building practices, says Corley, as more becomes known about the performance of the structure and its fire protection. For one thing, he said, “The more the fire resistance, the more costs go up and the less space available for use.”
Fire protection is an area that was stressed after the February 1993 bombing of the Trade Center.
A report on that explosion by the National Fire Protection Association said designers and code officials had special responsibilities with mega high-rise buildings because they expose tens of thousands of people to life-threatening conditions from a “single event.”
The fire protection specialists wanted designers and building code officials to “broaden their responsibilities to include security issues or other such subtle changes in our society in achieving dependable and reliable fire protection system performance.”
One of Corley’s jobs will be to advise on potential changes to building codes, if required.
