Structural Analysis of the Twin Towers

The building was designed to have a fully loaded

707 crash into it. That was the largest

plane at the time. I believe that the

building probably could sustain multiple

impacts of jetliners because

this structure is like the mosquito

netting on your screen door,

this intense grid, and the jet plane is

just a pencil puncturing that screen netting.

John Skilling, the structural engineer who designed the

Twin Towers, stated,

"Live loads on these perimeter columns can be increased more than

2,000% before failure occurs."

In particular, the Twin Towers were designed to sustain the impact of a

large airliner traveling at 600 miles per hour and still remain

standing. Interviewed in 1993 by The Seattle Times,

John

Skilling stated, "We looked at every possible thing we

could think of that could

happen to the buildings, even to the extent of an airplane hitting

the side.

Our analysis indicated the biggest problem would be the fact that all the fuel from

the airplane would dump into the building. There would be a horrendous fire.

A lot of people would be killed. The building structure would still be

there."

And it was. After the impacts, both towers remained standing,

showing no major effect on their stability.

The fact that they were designed to resist over 13,000 tons

of wind

pressure meant that they could not be knocked over.

Well, 13,000 tons is a lot of force.

People always talk about an airplane crashing into a building.

And in 1944 or 45, a plane did crash into the Empire

State Building.

But the largest aircraft flying today, at least commercially,

the 747 fully loaded,

is on the order of 300 tons. So if you think about a

300-ton element crashing into a building that's been

designed to carry 13,000 tons, you can see that

an aircraft crashing into the World Trade Center would probably not do

anything to the major building. It could affect localized structural

elements,

could knock out a column, and there could be some damage.

But as far as a plane knocking a building over of that type, that

would not happen.

It was the sturdiest thing. They weren't ever coming down.