Potential energy

[Pardalis]

The core didn't need support, it WAS the support for the rest of the building. It was fixed to the bedrock and cross braced. If it remained standing after the collapse, what force caused it to crumble?

I'm no structural engeneer of physicist, but in my layman opinion I find nothing odd about it. The whole building fell down around it, I don't expect anything to keep standing after such energy is released.

 

[defaultdotxbe]

The core didn't need support, it WAS the support for the rest of the building. It was fixed to the bedrock and cross braced. If it remained standing after the collapse, what force caused it to crumble?

wrong, the core was still braced by the floors and the exterior walls against wind shear and tipping

plus we dont know the amount of damage it sustained during the collapse, it could have easily been damaged to a point where it could no longer sustain its own weight

 

[einsteen]

I've often heard people about a core still standing, I've never seen that, only a few sticks still standing after the collapse, and they fall like mikado sticks after the collapse of the floors.

 

[westprog]

BTW, saying that energy is 'used' or 'expended' is a misnomer. Energy cannot be destroyed or created. When energy is caused to bend a piece of steel that energy does not disappear. It is transferred to the surroundings, it can be in the form of sound as air molecules bump against each other carrying the energy outward or in the form of heat. When you bend a steel coat hanger back and forth it gets hot and it cools off by dissapating that heat to the surrounding air or through infrared radiation. That is the energy from of your muscles being transferred to the coat hanger's steel lattice.

In the case of the collapses a lot of energy was carried away in the sound of the collapse, in the diffuse kinetic motion of the dust and a lot of it was transferred to the ground as heat.

I have no real idea of how the energy manifested itself. However, the fact that it was released answers most of the CT questions. "Where did the sound of explosions come from? Where did the heat come from? How was the concrete pulverised?"

If there is ample energy available for all these things, there's no need to look for additional energy sources - especially since (as was shown above) the amount of explosive needed to duplicate the effects of gravity would be both enormous and redundant - as a much smaller amount would suffice to pull the building. Er I mean collapse the building. Damn, gave it away.

 

[westprog]

R.Mackey,

Thanks, westprog, for starting this thread. I think the potential energy is one of the things that people have a hard time grasping (including me!)

The reason I did it was that I realised how easy the calculation was. mgh is one of the simplest formulae in physics. If anyone disputes my results, they can just go and do the calculation themselves, with whatever values for m and h they think appropriate. (I look forward to seeing some CT expert use a different value for g).

To clarify one minor detail. If we take the potential energy at the height H above the centre of the Earth, then we start with mgH. The building drops h giving a new potential energy of mg(H-h). The difference is thus mgh, which is the value I used.

 

[einsteen]

Jack Loizeaux (the godfather of controlled demolitions) about CDs: "We use explosives as the catalyst. But gravity is the engine."

With this he of course means that the energy is there already, it only needs to be released and that is possible to break the supporting structures.

ps. westprog, just take MgL/2 which give you about 1*10^12 J

 

[westprog]

Jack Loizeaux (the godfather of controlled demolitions) about CDs: "We use explosives as the catalyst. But gravity is the engine."

With this he of course means that the energy is there already, it only needs to be released and that is possible to break the supporting structures.

ps. westprog, just take MgL/2 which give you about 1*10^12 J

Apart from such a huge amount of explosives being quite impossible to smuggle into the building, it would be entirely redundant. A controlled demolition uses the minimum amount of energy to trigger a collapse. Using explosives to produce vast amounts of dust would be quite pointless. (Though I'm sure that a CT theory explaining how it would provide cover for nefarious deeds is just around the corner).

 

[jaydeehess]

The core didn't need support, it WAS the support for the rest of the building. It was fixed to the bedrock and cross braced. If it remained standing after the collapse, what force caused it to crumble?

That's a load of crap! The core could NOT stand on its own. It would be too tall for its width and contained little diagonal bracing between column.
For comparison the Windsor building in Madrid would fit inside the core of the WTC towers but was less than 1/3 the height of the towers.

The tower's core was never designed to be a stand alone structure. All buildings act as a system. The perimeter columns took about 40% of the dead load while the core took about 60%. The two column systems braced each other, neither could be a stand alone structure. The simplest illustration of such a thing would be a tripod. You cannot take out one leg of the tripod and have it remain standing yet each leg is certainly strong enough to carry its own weight and the weight of the other two.

Many CT's claim that the core took all of the gravity(dead load). That is simply erroneous and ridiculous. In order for this to be true the floor spans would have to be cantilevered out from the core which is not in evidence at all. Such an arrangement would be like each floor being a balconey with no side or diagonal support, and it would be a balconey that was larger than the support(the core).

The truss hat was designed to top off the bracing between the core and the perimeter and between perimeter sides. When the aircraft cut several perimeter columns then those columns could no longer transfer their load down through the perimeter to the ground and they instead were bascically hanging from the truss hat connections which meant that some of the load that the perimeter was originally carrying was now transferred via the truss hat to the core columns.

When the initial collapse started the impact on the beams, pans and columns of the next lower section was impacted by several thousand tonnes of material moving about 5-7 meters per second IIRC. This collapsed the floor pan and caused columns to buckle due both to the chaotic and large impacts to them not only from directly above but from side hits as the rubble shifted AND from the lost lateral support as the floor truss connections came away. In the case of the Windsor bldg the collapse started very high up meaning that the mass of falling material was much less than in the WTC towers and that the floor collapsed slower while pivoting about the connection to the concrete core columns which in turn were simply not affected by the heat as much as steel columns would be. In the towers some of the core columns were damaged or severed by the initial aircraft impact and others were heated by the fires. Although individual columns were heated on different floors(ie some on one floor getting heated mostly on the west side while the east side on that floor remains relatively cool But those cooler columns were being heated on another floor) the overall effect is a lessening of the ability of the core to support the mass above the fire floors. Same goes for the perimeter columns. Had the collapse of the towers been higher up, say six from the top then the falling mass would have been much less, the torsional forces would have been much less and the initial collapse could have been slower meaning a lot less released energy into the intact structures below. It is telling that the south tower went first. It contained just under twice the mass above the fire than did the north tower and suffered more core damage than the north tower.

 

[R.Mackey]

In case anyone's still wondering

I'm having difficulties with your value for kilograms of TNT, R.Mackey. The energy conversion factor I found (http://www.convert-me.com/en/convert/energy) was 4612 Joules per gram of TNT, unlike your value of 4184. Where did you get your value?

After thinking about it, I believe the difference between your TNT figure and mine is one of units. Mine was 4184 kJ per "ton," but now I believe that refers to an Imperial ton, as opposed to "1000 kg." The 11% discrepancy between your figure and mine seems consistent with the weight ratio.

So my conclusion of total tower GPE = approx. 160 tons should be revised to 146 metric tons, or 146,000 kg of TNT.

Lousy screwball Imperial units! It's a wonder we can communicate with each other at all...

 

[beachnut]

The core didn't need support, it WAS the support for the rest of the building. It was fixed to the bedrock and cross braced. If it remained standing after the collapse, what force caused it to crumble?

Core was not made for lateral support! Simple, the shell was for lateral support, the core mainly for gravity support.

You did not study this much. Thus a bare core would fall in the wind; a simple light wind.

Simple easy, no lateral support, why do some not know?

 

[A W Smith]

Core was not made for lateral support! Simple, the shell was for lateral support, the core mainly for gravity support.

You did not study this much. Thus a bare core would fall in the wind; a simple light wind.

Simple easy, no lateral support, why do some not know?

I think it's a problem with scale for some. If any have stood very close to the building or even some distance away you get an idea of just how gigantic and tall they were. Even when I took the water taxi from the marina on the Hudson which is some distance away I had to almost lean back to see the top. You are right beachnut a simple stick framed core 87 feet by 137 feet would not stand on its own at that height. With even a light breeze It had no shear capacity.