A new way of looking at the Pentagon: How the building itself saved lives on 9/11

ARLINGTON, Va. (WJLA) — Exactly 60 years to the day before the September 11th attacks, crews broke ground on one of the most iconic symbols of our nation's strength.

On September 11, 1941, the Pentagon was born.

This 6 million square-foot structure was built to withstand heavy loads on the inside, with floors made to support millions of pounds of documents.

Little did early 20th century designers realize their unique approach would help the Pentagon defy the physics of building collapse.

"Can you imagine the plane crashing into a building at the first floor and the building doesn't collapse immediately? Why is that?" asked Don Dusenberry, as he and his team of elite structural engineers set out to answer those questions and more when they were asked to examine the Pentagon after 9/11.

It was rubble to the untrained eye. To Dusenberry and his team, the remnants of the building were pieces of a puzzle.

“You look for cracks,” said Dusenberry. “You look for missing concrete. There were columns lying on the floor that pointed in a certain direction. That direction showed what direction the plane was coming and what remained told us a story."

The plane hit the building at 500 miles per hour.

“It was amazing to think how controlled the attack was by the pilot of this plane thinking, I’m sure, if he could bring it in on the first floor it would do the most damage to the building,” said Dusenberry. “Fact is, maybe that induced less damage than if he had it the building at a higher level.”

Here's why.

Dusenberry and his team discovered the Pentagon was built with concrete columns much closer together than in modern construction, with one continuous piece of spiraled steel on their interior, allowing concrete and other reinforcements to remain contained. The result: they bent instead of broke, preventing catastrophic collapse.

“It was just unbelievable,” said Dusenberry. “They were bent three times their diameter, bent laterally, and they were still there."

Other unintended structural supports, he says, also played a huge role in blunting the force of the plane. Exterior walls of the building were filled with unreinforced brick, which Dusenberry says turned the walls essentially into giant beams that kept the walls of the building from turning when the plane hit.

And instead of a traditional floor structure, with beams going only one way, the Pentagon floors were built with spans going in two directions.

“It gives it a second means of support,” said Dusenberry. “It's more like a net. If you were to take out columns underneath, which is what happened, it's more like a net and it's held on all four sides."

And that "net," says Dusenberry, made all the difference. The former President of the Structural Engineering Institute of the American Society of Civil Engineers has no doubt without those structural features, far more lives would have been lost.

“Without question,” said Dusenberry. “They had about 20 minutes to get out. And as far as I know, everybody on the third, fourth and fifth floors got out. That wouldn't have happened if the building had collapsed immediately."

Since 9/11, Dusenberry says there's more attention paid to design with catastrophes in mind.

And he says the structural elements revealed at the Pentagon provide battle-tested evidence that can be applied to modern-day construction.

“The ability to deform, to very high degrees without fracture and the columns and beams in the Pentagon had that, that feature," Dusenberry says. "This may be the key feature to trying to keep a building erect, if it's been significantly damaged."

The other sites struck by terrorists on that fateful day have been completely transformed, but the Pentagon remains, still a symbol of American strength and a reminder of just how much can be learned from the past.