The 9/11 Forum

dadeets wrote:1. Being responsible for the 35 m/s which supposedly was through direct contact with a free structural element strains credulity.

Why ?

Look at what happens to the WTC2 perimeter when the rilted upper section drops and acts as a "wedge"...





That's a mighty big piece pushed rapidly outwards, via a known and visible action...

SanderO wrote:I think femr2 needs to do some traces and confirm the velocity.

No worries. When I have time.

Two similar structures cannot wedge. I often hear the terms funneling, wedging but never an explanation about how that happens, but this is a nice animation, I've seen it often. To me it explains that the core sections of both the top and bottom are removed.

Eistein...

Why core sections removed to explain that facade motion? The facade is either falling away or being pushed away or both in some proportion. Why would a disappeared core impart a horizontal component to the facade?

One explanation could be the crashing down floors AND pressurized the air and exerted the outward push... as in pouring something into a container which had walls which could not contain it.

Or perhaps the facade and floors from above of the upper section IS siding down AND wedging the facade off?

Maybe a bit of all three causes?

But this gif is incredible in that it shows how the facade is being moved away very rapidly.

einsteen wrote:Two similar structures cannot wedge. I often hear the terms funneling, wedging but never an explanation about how that happens

I doubt they would be classed as similar a few seconds in...


"Wegding" certainly appears to be at work here. The red lines may help.

Most likely the beam-framed floor area (108-110) in combination with hat truss acting here as 'thruster'.

Ok, maybe I am not clear, there could be an initial wedging effect.

This is always the picture that I have in mind when thinkg about the WTC cores. Inner and outer cores with their own resp. purposes.



First of all the initiation problem is a different thing but assume it happens locally due to a local defect we are still having
an intact building outside of that impact area. A failure will lead to a new stable situation but one assumes a tresshold to overcome
which leads to 'the towers are doomed after that'

Now look at this, what is going to wedge? Funneling is possible when a structure that stays intact is able to fall into an open tube structure.
We believe that both sections don't stay intact (even the Bazant model assumes that and it must assume that because otherwise buildings don't fall...)
and that implies there is no wedging effect. It debunks the whole idea of complete funneling.





Only rubbish will fall on an intact building. One of the leading models (Dr.G where are you...) is that we have a top
section that will collect floors on its way down to the bottom and will together with a compacted layer of floors unrip the next floor and so on.
This is in fact the discrete Bazant model, but this is not funneling.

An intact top section is IMHO only able to funnel through a building if the inner cores are removed. It looks indeed that is the
case in your picture which means the Bazant model couldn't hold. Or is there an other explanation using the above picture ?

The top doesn't REMAIN intact as it drops and wedges. It comes apart IN THAT PROCESS.

The initiation doesn't disintegrate the top *block* in an instant. It gets them moving and crushing and interacting with the structure below. It's like a car slamming into another car.... in the process each structures loose their integrity.... one car doesn't remain intact as it penetrates the other... it's parts enter and destroy and fling both car's parts allover the place.

The MASS of the *top block* can *funnel* whether there is a core there or not. The core is essentially a bunch of sticks - 47 of them.. once the alignment with the columns above has been offset the core below down hardly a thing in resisting the top coming down. And the core had large voids as it contained vertical. Look at the sticks in the attached framing plan.

It certainly doesn't remain as a rigid block and crush the bottom like a solid intact pile driver.

I've studied the Bazant collapse and can reprouce exactly their result that's not the problem. In Greening's old paper (which is in fact a discrete model of it) he assumes a top section that stays intact, collect floors and finally the top section will be imploded when it hits ground zero. Thats a model, great. A more complex model in which the top section also will collapse, say with a slower rate than the part below will also do the work. But these model assume uniform structures and assume some other things. Well, your rubble model is exactly also that model, but that means that the wedging of the animation is an extrapolation of the mind.

I think it is very hard to imagine how that top section with its mass and intact core columns structure could fall through the rest. Are you serious if you think that an offset will explain the funneling phenomenon? First of all there is no offset at initiation, secondly the core structure is no sticks structure, but heavily braced. Look at the picture and think about it. Also since the core is collapsed in the same rate as the floors, that also means the accumulated core structure of the stories below needs to be taken into account. Also remember that the core is strong enough to hold a complete building. It is better to start with a model consisting of two kinds of material. If you drop the top section with only the cores on the lower section it will certainly topple away from the building. After 10 years I still haven't seen a good explanation of the collapse. If the core is removed first from top to down all observations fit.

The core up there was pretty much sticks...and the bracing... was what supported the floors...floors go... bracing goes and your have sticks trying to pick up the loads of the other sticks.. misaligned ... no cigar..minor misalignment buckles them.