Re: 9-11 Wackos

The columns were designed to hold the total load with regular/uniform unbraced lengths (i.e. the floor to floor heights). Load was redistrubuted due to the impact of the plane. Unbraced lengths of columns changed due to failure of the trusses falling down from the fire and also the weakening of the steel due to heat (notice I didn't say MELTING).  Then the first collapse or buckling takes place and stuff starts to move down when Mass (increasing @ each floor) x Acceleration (constant) takes over. Momemtum ( increasing mass x increasing velocity) @ each floor overcomes the static load capacity of the floors while the impact is a continuously concussive force on the overloaded columns that have to top stability as the building comes down. Like crushing a can of soda over and over only the crushing force increases each time. WTC-7, 100 yards away was hit with debris, so there was no clean true pancaking.

If the building tipped over like a tree being cut, it's obviously more clear cut. But the structure was damage up high, not at it's base.

According to the little bit I've watch from the popular mechanics guys, the WTC 7 building had about 25% of its lower support obliterated from debris of the falling towers. They also say in layman's terms, that it had very little axial redundancy at its base due to being built over an adjacent structure, so it had only a few main columns at it's base

That's how I see it and it makes sense to me.
-g

On 5/25/07, ECVAl3@aol.com < ECVAl3@aol.com> wrote:

Lets say the floors give way instantaneously due to the increase in mass plus increase in acceleration and it all falls to the ground as if in free fall. Weren't the interior and exterior columns designed to support the total weight (live + dead load) of the structure above each level and if the floor structure instantaneously separated from the columns wouldn't the majority of the columns still be standing, even momentarily, after the floors collapsed? Wouldn't the steel columns on the exterior of the building flex and twist, possibly snapping and fly considerable distance from the building or fall away from the building mostly intact?

 

The videos don't show this type of behavior. Why not?

 

S.Macie, CA.P.E., HI.S.E. 

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-gm