Some Calculations requested regarding why the towers upper portion did not slide off

[einsteen]

Straw man

 

[jsfisher]

The counter would be to say the orbital weapon was in geostationary orbit, and thus stays over the same part of the Earth's surface all the time. The problem there is that geostationary orbit requires a much larger distance from the Earth; low Earth orbit is at an altitude between 124-1,240 miles but geostationary orbit is at an altitude of 22,300 miles. That's more some 18 times further away than the highest level of LEO. Being that much further away greatly complicates the aiming process as well as greatly increasing the power required by this supposed weapon.

Not only is the aiming more a problem from 22,300 miles, the weapon, itself, would need to be over the equator to be in a geostationary orbit. The energy beam fired from the weapon wouldn't be straight down on either tower. At best it would be 47 degrees from vertical.

 

[Newtons Bit]

Straw man

Are you going to explain yourself? Or just keep speaking gibberish and going "nyah nyah nyah" with your fingers in your ears.

 

[einsteen]

Are you going to explain yourself? Or just keep speaking gibberish and going "nyah nyah nyah" with your fingers in your ears.

Don't you understand how big the difference between two stories should be if only the current story i is crushed and not i+1. OCT'ers always correctly mention the difference between static and dynamical forces, now what do we have now, say we are at 3/4 of the collapse and a complete building's mass collapses with 40 m/s on a floor and still only that story breaks. The collapse model says (by definition!) it doesn't affect the one below that one in the slightest way.

 

[Dave Rogers]

Scale models are also used in wind tunnels, of course you are right that it is hard to scale the wtc, you should scale each floor's mass with the same factor, the energy values E1 with the same factor, gravity cannot be scaled, but the system is invariant as long as gh is constant, i.e. h the distance between the floors. You should place the model in a centrifuge.

And then the truth movement replies, "They built a scale model of the towers, but they had to put it in a centrifuge to make it collapse! They cheated!! It doesn't prove the real towers would have collapsed!!! Gravity doesn't change!!11!!! PWN3D!!ELEVENTYONE!11!!"

Either you build a scale model, scaled in linear dimensions only, and it doesn't collapse, so the truth movement claims the test proves the real towers wouldn't have collapsed, or you build a model with adjustments so that the scaling of material properties, forces and energies is correct, in which case the truth movement claims the model was adjusted so as to ensure collapse. And so it will never, ever be possible using scale models to advance any evidence for global collapse that the truth movement will accept. As for the serious structural engineering community, they already accept that global collapse is a reasonable outcome anyway. So any attempt at analysis using scale models, from the point of view of the 911 truth debate, is completely pointless.

Dave

 

[einsteen]

Good point of course Dave.

 

[Belz...]

My thread was on Greening's paper. In it, he said there was a top block which remained intact until it "crushed down" through the lower building, all the way to the ground. Then (and only then), the top block itself underwent "Crush Up".

Greening has been forced to abandon this idea. How any honest person could have ever entertained it is beyond me, precisely because of observations such as are made in the graphic posted by Rev.

Indeed. Same with concepts such as "dustification".

It was WTC7 that imploded into its footprint. The twin towers exploded.

I think the word you're looking for is "collapse".

Scientists require evidence.

And you're evidently not a scientist...

 

[Belz...]

Here's a challenge: build a vertical structure such that when you impact it from above with a sledge hammer, it collapses "floor by floor" with no visible damage below the impacted "floor".

Uh-huh. Build it full scale, and see what happens.

 

[Belz...]

Straw man

Gosh, you truthers love to say that.

 

[Newtons Bit]

Don't you understand how big the difference between two stories should be if only the current story i is crushed and not i+1. OCT'ers always correctly mention the difference between static and dynamical forces, now what do we have now, say we are at 3/4 of the collapse and a complete building's mass collapses with 40 m/s on a floor and still only that story breaks. The collapse model says (by definition!) it doesn't affect the one below that one in the slightest way.

Sorry bud, if one column has a compressive strength of 1200 kips and the one below 1205 kips, the one below will not buckle and the one above will. The point in which a column is the peak axial force it can resist and transmit. The column below CANNOT buckle if there is not a high enough load applied to it. If a column does not buckle, it remains in the elastic stress-strain region. It does not permanently deform. This is BASIC mechanics.

(i+1)/i could be as small as 1.01 and it would, theoritically, be the same.

 

[einsteen]

I re-readed NB's post and he is probably correct that an increasing strength could be play a role in the stepwise collapse. And I made the mistake that the energy and momentum of the collapsing mass has nothing to do with the force itself, apologies. (I came to the exponential thought because of this, but math should be worked out precisely first) But then if you use a linear behaviour and also assume that the E1 values are also lineair then you of course have a simple linear function. Some input then is needed to calibrate the function. The linearity is also consistent with the normal static forces that the building should handle, assuming the floors have equal mass. To be continued.

ps. You posted while I was typing...

 

[einsteen]

I'm still wondering if you do this experiment for Spaghetti with a linear increasing strength

http://www.math.psu.edu/belmonte/sg9.gif

 

[Newtons Bit]

I'm still wondering if you do this experiment for Spaghetti with a linear increasing strength

http://www.math.psu.edu/belmonte/sg9.gif

It cannot be one long skinny tapering rod. It needs to be non-slender columns supported by a floor diaphragm. Each column in a column line the buckles individually.

 

[einsteen]

Newtons, There is something to add to the story. Even if you have a theoretical 1d model in which each story's force increases lineair to the bottom, we are still talking about a coupled system. The maximal force reached is not something that is part of the dropping block, that depends on the whole reaction of the building, a story only reaches its maximal force if you compress it, but before it reaches its maximal force the artificial theoretical model will also be compressed at lower levels and the maximal force is not reached. I think the situation is too complex and could only be solved with coupled differential equations. You can set them up, but what then...

 

[lozenge124]

Sorry bud, if one column has a compressive strength of 1200 kips and the one below 1205 kips, the one below will not buckle and the one above will. The point in which a column is the peak axial force it can resist and transmit. The column below CANNOT buckle if there is not a high enough load applied to it. If a column does not buckle, it remains in the elastic stress-strain region. It does not permanently deform. This is BASIC mechanics.

Well, it's not as clear cut because the lower column has to carry the upper one so it depends how heavy the top column is - this is added stress on the lower one. Additionally, the WTC columns were also carrying the weight of the floors and in the chaos of the collapse, with the upper block tilting over, the very upper floors (connected to the upper column sections) could have been damaged/compromised resulting in LESS compression on the upper sections than the sections below still carrying their full floor load. This could result in lower columns buckling before the upper ones.
So, it doesn't seem to me to be that simple, especially when you consider the spandrels tying the columns together in larger units etc.

Also, in looking at pictures of the collapse and the debris afterwards, it seems that many (most?) of the perimeter columns were relatively straight and failed at the bolt connections.

Does this jive with your concept of the uppermost columns buckling? It seems to me not - to explain this I think you have to consider at least 2 columns "buckling" as a unit in a v-shape until the bolts are torn off.

We also know that a huge chunk of the North tower was ejected with tremendous horizontal velocity enabling it to travel 390ft and embed itself partially in the WFC building:

http://youtube.com/watch?v=wW55hdXUJvk)

Can this kind of event be explained in terms of vertical, gravitational forces alone without invoking horizontal explosive bursts? Maybe, but IMHO it requires more work than what has been seen up to now.

 

[Belz...]