- The Washington Times - Friday, December 21, 2001

Osama bin Laden and Hyman Brown were as they told it the most surprised engineers in the universe when the World Trade Center collapsed.

Mr. Brown, who watched from his Colorado office on September 11, spent six years overseeing construction of Tower 1 and most of Tower 2 and believed them to be indestructible, particularly after the 1993 bomb attack that was meant to fell them.

Bin Laden, who monitored that deadly day from an Afghan hide-out, was believed to have directed the assault that knocked down the towers, and he insisted that result exceeded his fondest hopes.

"As I watched this collapse, I thought, 'This is not possible,'" Mr. Brown said in recognizing a likely truth: Before that terrible Tuesday, bin Laden alone recognized a vulnerability that would still puzzle investigators.

"He has the same training we all have, but we never think of destroying a building. We make sure it stands up," said Mr. Brown, who teaches his profession at the University of Colorado in Boulder and is involved in analyzing the structure's catastrophic failure.

Mr. Brown said he fully believed bin Laden's videotaped boast that he expected burning aviation fuel to superheat the steel supports that buckled like cooked noodles and collapsed the floors above where the planes hit.

He also accepted bin Laden's claim that he never realized the sneak attack would demolish the twin towers as he attempted to do with the 1993 bomb. That attack only reinforced beliefs that the buildings were safe.

"I was thinking that the fire would melt the iron structure of the building and collapse the area where the plane hit and all the floors above it only. This is all that we had hoped for," bin Laden said in an amateur videotape.

"In his own criminal way, it was brilliant," Mr. Brown said of the deaths of two buildings that were designed to withstand the force of a jet airliner's impact with no thought to the inferno that followed.

"No one thought in 1965 of protecting a building from burning aviation fuel. It never ever entered our mind," Mr. Brown said.

Debris above the presumed fire line 60,000 tons above floors 90 to 94 in Tower 1 to the north and 110,000 tons above floors 78 to 84 in Tower 2 to the south had a free fall of 50 feet or more into areas the Boeing 767s ripped open.

"That is basically what bin Laden said would happen, but when you have 60,000 tons or more falling 52 feet, no design can withstand that," Mr. Brown said.

He said bin Laden simply failed to "calculate the impact load" of so much falling steel and concrete that flattened two 110-story buildings.

Not every informed participant in the postmortems was convinced bin Laden anticipated the fire's importance. One who insisted on anonymity because he was a key investigative leader said, "I would doubt that somebody would have been able to anticipate that."

Other investigators focused on evidence that chronic problems with fireproofing left the central core overly vulnerable to fire, reducing escape time.

When the 1,368-foot north tower was completed in 1972, it was the world's tallest building, a mantle assumed two years later by the Sears Tower in Chicago.

The skyscrapers were the first designed without structural masonry, and relied instead on an outer framework of steel columns like those at Seattle's IBM Building. Floor trusses linked the outer frame to the reinforced-steel central core.

"It was the first time that design was used and provided 60 feet of clear space inside with no columns. Without the fire, those planes could have broken most of the outer columns and the building still would stand," Mr. Brown said.

"Steel melts at 1,600 degrees Fahrenheit, but there is nothing normally in a building that burns at temperatures higher than 1,200 degrees. He brought in aviation fuel that burns at 2,000 degrees and knew it would bend the beams," he said. "It's never happened before, so I don't think we have tested steel enough at 2,000 degrees Fahrenheit. At 2,000 degrees, nothing stands."

NASA shuttle orbiters routinely survive temperatures up to 3,000 degrees Fahrenheit during their plunge back into Earth's atmosphere, but exotic thermal tile insulation keeps internal structures below 350 degrees.

"It would cost so much for tiles to make buildings that safe it would be impossible to make a building pay for itself. We build skyscrapers to make a profit," said Mr. Brown, who served as vice president for budgeting, estimating and construction at Tishman Realty and Construction, the firm that supervised World Trade Center construction.

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