The North Tower Impact Pictures

This could possibly be the answer folks depending on whether the steel was high strength or regular structural steel.

Structural steel Ultimate strength = 400 MPa
High strength steel Ultimate strength = 760 MPa

Aluminum alloy Ultimate strength = 455 MPa

Source: en.wikipedia.org...

Note that this is tensile strength.

Shear could be different.

In general: ductile materials fail in shear (ex. aluminum), whereas brittle materials (ex. cast iron) fail in tension. See tensile strength.

en.wikipedia.org...

Actually, the steel would be under shear while the plane is under compression. Still looking to see if I can find easy numbers to verify.

But, I believe that since aluminum fails in shear that the Ultimate strength of aluminum would be in shear and since steel fails in tension first, the ultimate strength is in tension. So, the shear strength of steel could be higher. Still looking into it. It's been a while since I've had materials science.

Thank you for the many replies thus far, there have been some very interesting comments, if I could add a few more.

We have all seen lab tests where everything from a flake of paint too a piece of 4x2 is fired at very high velocity that penetrates many materials, but thats just it its done in controlled conditions.

Secondly a while back I watched a documentary of a plane surving an fuselage fire. I think the test was done in the US and basically a jumbo was remote flown into a series of steal supports desinged to open up the fuel tanks and plane and to observe the flow of fire into the plane.

Well needless to say the plane was shredded and disapeared in a ball of flame but there was very little damage to the steel structure, any comment on this.

Originally posted by magicmushroom
Thank you for the many replies thus far, there have been some very interesting comments, if I could add a few more.

We have all seen lab tests where everything from a flake of paint too a piece of 4x2 is fired at very high velocity that penetrates many materials, but thats just it its done in controlled conditions.

Secondly a while back I watched a documentary of a plane surving an fuselage fire. I think the test was done in the US and basically a jumbo was remote flown into a series of steal supports desinged to open up the fuel tanks and plane and to observe the flow of fire into the plane.

Well needless to say the plane was shredded and disapeared in a ball of flame but there was very little damage to the steel structure, any comment on this.

I think it's safe to assume that since the whole point of the exercise was to test fire retardant additives in the fuel, that they wanted the steel beams that were imbedded in the ground to survive the encounter so that they could do their work of shredding the plane.

I also think it's safe to assume that NASA engineers are a smart enough bunch to figure out what the impact forces would be in the crash and design a system that would survive the crash.

Haroki thats just the point the steel was secondary to the plane in the test so it did not matter if it survived what matters is that a plane travelling at high speed made llittle impact on the steel structure.

Originally posted by magicmushroom
Haroki thats just the point the steel was secondary to the plane in the test so it did not matter if it survived what matters is that a plane travelling at high speed made llittle impact on the steel structure.

Well, if the beams would have broken off at the first touch, NASA probably wouldn't have gotten the data they were looking for.

What speed did they crash the planes? I see no evidence that they were doing 450mph. Would have been a little rough to control a plane by remote control like that when the pilot's looking through a tv screen. I assumed they were recreating a crash landing where the pilot was attempting to lessen the impact.