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Build a Safer Skyscraper

The 9/11 attacks threw the architectural world into shock. “The age of skyscrapers is at an end,” city planner Howard Kunstler declared just after the tragedy, and Donald Trump reduced the height of a planned tower in Chicago, citing security concerns raised by 9/11.

But since the tragedy, architects have used advances in construction materials and new designs to make tall buildings safer -- and more likely to withstand a 9/11-style attack. 

“Certain things that were virtually unheard of 15 years ago are now pretty routine,” Architectural expert Martin Moeller, senior vice president of the National Building Museum , told FoxNews.com.

“Take the typical cement sidewalk. It might be able to resist a couple thousand pounds per square inch. There are now concretes that resist 25 thousand pounds per square inch,” he said.

Very high-strength cement can help a building resist the type of impacts caused on 9/11 by protecting the steel that holds skyscrapers together -- the weak point in the attacked towers.

“It was the heat of the fire which severely weakened, ultimately beyond repair, many of the steel elements that not only held the floors up but kind of held the building together,” Moeller told FoxNews.com.

The steel beams of the old World Trade Centers were insulated from fire with fire-retardant chemicals that make it look like it was covered in foam. But that didn’t work very well.

“That may be fine for a warehouse,” Moeller said. “But on 9/11, when those planes flew into the buildings, the foam was just blown off. Now, there are other ways to protect the steel.”

For instance, in 7 World Trade Center -- the first of the destroyed buildings to be rebuilt, in 2006 -- three feet of concrete now surround the steel core.

Steel has also been getting stronger, as scientists have gradually found better alloys. A new discovery this year by an entrepreneur in Detroit found that rapidly heating and then cooling steel in the factory made it 7 percent stronger. Gary Cola, the inventor, has named his new steel “Flash Bainite.

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