Split Thread Mistakes in David Chandler's analysis of the WTC collapse

[alienentity]

Kylebisme,

You're making a critical error. The towers are not a homogenous solid elements. A force applied at one corner of the building will not apply a large amount of moment to the upper block for two reasons:

1) the individual elements in the lower block will fail and become disconnected from the lower block.

2) the individual elements in the upper block will fail and become disconnected from the upper block.

You can't treat the problem as a solid block (which is what you're doing). It must be analyzed with discrete elements that have finite amounts of strength.

Hey Newton, would you be kind enough to point out the incorrect physics in this statement of David Chandler's. I know it's a bit OT.

'The roofline of WTC1 (The North Tower) begins dropping with sudden onset and accelerates uniformly downward at about 64% of the acceleration of gravity (g) until it disappears into the dust. This means it is meeting resistance equal to about 36% of its weight. The implication of this, however, is that the force it is exerting on the lower section of the building is also only 36% of the weight of the falling section. This is much less than the force it would exert if it were at rest. The acceleration data thus prove that the falling top section of the building cannot be responsible for the destruction of the lower section of the building'

I'm especially curious how Chandler can present himself as a serious thinker with this kind of faulty reasoning.

Another comment I'd appreciate is on Chandler's claim at :44 in this video

http://www.youtube.com/watch?v=6_B_Azbg0go#t=30s

Split from: Tower Collapse Questions for Critical Thinkers.

Posted By: Gaspode

 

[jhunter1163]

Hey Newton, would you be kind enough to point out the incorrect physics in this statement of David Chandler's. I know it's a bit OT.

'The roofline of WTC1 (The North Tower) begins dropping with sudden onset and accelerates uniformly downward at about 64% of the acceleration of gravity (g) until it disappears into the dust. This means it is meeting resistance equal to about 36% of its weight. The implication of this, however, is that the force it is exerting on the lower section of the building is also only 36% of the weight of the falling section. This is much less than the force it would exert if it were at rest. The acceleration data thus prove that the falling top section of the building cannot be responsible for the destruction of the lower section of the building'

I'm especially curious how Chandler can present himself as a serious thinker with this kind of faulty reasoning.

Another comment I'd appreciate is on Chandler's claim at :44 in this video

http://www.youtube.com/watch?v=6_B_Azbg0go#t=40s

Where'd the other 64% go? Just hovering in the air over the lower section?

 

[GlennB]

Where'd the other 64% go? Just hovering in the air over the lower section?

Everybody knows things get lighter when they fall. D'oh !

Funnily enough Chandler's truly frightening gibberish reminded me of something interesting I noticed in an action film a long time ago. 'The Pride and the Passion' it was, based on the C.S.Forester novel 'The Gun' and starring Cary Grant, Sinatra and Loren (dreadful poxy film with Sinatra totally failing to sound like a Spaniard).

Anyhoo .... the rebels are hauling a massive cannon overland to liberate somewhere or other. The British Naval officer with them warns that hauling it uphill might be a real bitch, but it "gets heavier going downhill". The rebels laugh at the logic of this, but the moment they fail to control it going downhill the thing roars away down the slope out of control. It ends up in a flower meadow ... cue silence except for a bird twittering.
"Gets heavier..." might have been badly put, but we know what he meant.

More pseudo-scientific gibberish, just to show how easy it is :

As we know, force = mass x acceleration. f=ma

When the upper section was at rest prior to collapse, it wasn't accelerating at all. Substituting 0 for a, the upper section was exerting no force whatsoever. This is true all the way to the ground, so we can conclude that the WTC was seriously over-engineered. By about 100% in fact (in the vertical plane anyway)

Wonder if Chandler reads this stuff?

 

[Newtons Bit]

Hey Newton, would you be kind enough to point out the incorrect physics in this statement of David Chandler's. I know it's a bit OT.

'The roofline of WTC1 (The North Tower) begins dropping with sudden onset and accelerates uniformly downward at about 64% of the acceleration of gravity (g) until it disappears into the dust. This means it is meeting resistance equal to about 36% of its weight. The implication of this, however, is that the force it is exerting on the lower section of the building is also only 36% of the weight of the falling section. This is much less than the force it would exert if it were at rest. The acceleration data thus prove that the falling top section of the building cannot be responsible for the destruction of the lower section of the building'

Chandler makes the same mistake. He is assuming, whether knowingly or not, that the upper block is one rigid element. When the upper block impacts, the lower block will apply a force to the upper block equal to the maximum capacity of either the elements in the lower block or in the upper block. These elements will break. The roof-line will continue to accelerate at g, except during the time in which a force is applied through an element before it breaks, in which it is: g - (vertical force applied to elements/mass of the total structure). Considering how much of the WTC is just empty air, it is not surprising that the majority of the collapse is near free-fall and thus averages out to something near free-fall.

The truly idiotic thing about Chandler is how he doesn't even examine his own statement for the limit case. If the lower block was actually resisting the whole weight of the upper block as he states should happen, the acceleration would thus be zero. And thus nothing can collapse, ever, by his phony logic.

I'm especially curious how Chandler can present himself as a serious thinker with this kind of faulty reasoning.

Another comment I'd appreciate is on Chandler's claim at :44 in this video

http://www.youtube.com/watch?v=6_B_Azbg0go#t=30s

I think there are some others here that have addressed how the piece of debris appears to be accelerating quickly due to camera angles.

 

[alienentity]

Chandler makes the same mistake. He is assuming, whether knowingly or not, that the upper block is one rigid element. When the upper block impacts, the lower block will apply a force to the upper block equal to the maximum capacity of either the elements in the lower block or in the upper block. These elements will break. The roof-line will continue to accelerate at g, except during the time in which a force is applied through an element before it breaks, in which it is: g - (vertical force applied to elements/mass of the total structure). Considering how much of the WTC is just empty air, it is not surprising that the majority of the collapse is near free-fall and thus averages out to something near free-fall.

The truly idiotic thing about Chandler is how he doesn't even examine his own statement for the limit case. If the lower block was actually resisting the whole weight of the upper block as he states should happen, the acceleration would thus be zero. And thus nothing can collapse, ever, by his phony logic.



I think there are some others here that have addressed how the piece of debris appears to be accelerating quickly due to camera angles.

Thanks! I worked out the expected collapse time based on Chandler's observation, using 6.278m/s^2 (64% of g) and 416 metres. I arrive at an expected time of 11.51 seconds if that were consistent.

That's not far from Bazant's numbers, within 8% I think. So I don't think Chandler's measurements do anything to disprove mainstream understanding of the collapse time.

I take it your comment 'If the lower block was actually resisting the whole weight of the upper block as he states should happen, the acceleration would thus be zero.'
refers to Chandler's assertion that 'the force it is exerting on the lower section of the building is also only 36% of the weight of the falling section.'

It seems to me if Chandler were correct, the verinage technique of demolition would be impossible.

What of Chandler's apparently contradictory statement (in the video I linked to) that an object in freefall (he's referring to the upper block) is experiencing no forces, so shouldn't break apart, yet meanwhile the block is impacting the structure below.
He seems to be arguing that it's impossible for it to be in freefall without explosives, yet impossible to be slower than freefall without explosives..

I can't figure out why people are actually listening to this guy. His arguments make no sense to me.

 

[triforcharity]

Oh, I know, I know.

The problem with Chandler's video is, Chandler did it. That is the whole problem.
Fail from the word go.

 

[Dave Rogers]

Hey Newton, would you be kind enough to point out the incorrect physics in this statement of David Chandler's.

A question about physics, and you're asking an engineer? Sometimes I wonder why I bother.

Anyway, it's a simple error that Chandler's making; he's confusing instantaneous and local forces with time- and position-averaged forces, and claiming that one has to equal the other. I'll put some more detail round that.

The roofline of WTC1 (The North Tower) begins dropping with sudden onset and accelerates uniformly downward at about 64% of the acceleration of gravity (g) until it disappears into the dust. This means it is meeting resistance equal to about 36% of its weight.

Assuming the acceleration is correct (it appears perfectly reasonable), then this is OK so far with one correction: it means that the upper block is meeting an average resistance equal to about 36% of its weight. It's the omission of one simple concept - that the resistance can vary over time, and that the average acceleration only measures the average resistance - that is the fatal flaw in Chandler's reasoning.

The implication of this, however, is that the force it is exerting on the lower section of the building is also only 36% of the weight of the falling section. This is much less than the force it would exert if it were at rest.

Again, no problem with this except that the word "average" is needed.

The acceleration data thus prove that the falling top section of the building cannot be responsible for the destruction of the lower section of the building

I'm especially curious how Chandler can present himself as a serious thinker with this kind of faulty reasoning.

What's notable about this bit is not that the reasoning is faulty, but that it's omitted entirely. Chandler makes an unjustified leap of logic here, leaving it for his critics to reconstruct the line of reasoning, and hence fall foul of strawman accusations - a classic pseudoscientist's trick. So, bearing that in mind, what Chandler appears to be reasoning is that the lower structure is capable of exerting a maximum upward force in excess of the weight of the upper block, and hence cannot be crushed by it.

I like shopping analogies, so here's a good one. A family earns $2000 per month, and spends $1250 per month on groceries. They're struggling to stay out of debt, so they end up the month with all their money spent. On average, therefore, they have a bank balance of $1000. Where did that $1250 come from for the groceries?

The answer to both is that the value of a variable at a specific instant can be bigger or smaller than its average value. (That's what I mean by "the instantaneous force"; the value of the force at a specific moment.) In the case of the falling tower, then upper block can exert a force very much greater than its weight for a small proportion of the time, then none at all for the rest of the time. So: it falls on a column, or group of columns, and the impact slows it down. The columns compress, buckle and break, and suddenly it isn't resting on anything, so there's no force exerted. It falls freely until it hits the next group of columns, and the same thing happens again.

Tony Szamboti claims that this will result in jerks in the movement of the top block, but that's wrong too. If the top block falls perfectly level, so that it hits all the column tops at the same time, then there's a visible jerk as it breaks them; we see this in verinage demolitions, where the collapse is initiated very precisely so that the top block doesn't tilt. The WTC collapses were much more messy, consistent with an uncontrolled collapse initiation, so the top blocks fell at an angle. The column impacts, if indeed they happened at all, didn't happen all at the same time, so the jerk was spread out; in fact, it was so spread out that it couldn't be seen at all.

So what really happened is that the forces between the top and bottom blocks varied with time and position, from very large in some places and at some times, to nothing at all at others. David Chandler's mistake is to assume that there was just a single average force, and that this was evenly spread across time and position. If that had been the case, there couldn't have been a collapse; but once the structure was weakened enough for collapse to begin, and once the upper block had started to tilt, it couldn't possibly be the case any more.

Dave

 

[Sam.I.Am]

My interpretation of the north tower collapse is that it tilted slightly inwards towards the south then southeast (using the antenna as a compass) with the block crushing slightly towards the northwest as it collapsed.

 

[alienentity]

Thanks Dave.

Chandler's also assuming that the strength of the columns is not compromised, and that the impact (and resistance) would be evenly distributed onto the structure below.

Neither of those things are true. Therefore it isn't impossible for the upper block to accelerate somewhat slower than freefall as it begins to fall.

 

[bill smith]

Thanks Dave.

Chandler's also assuming that the strength of the columns is not compromised, and that the impact (and resistance) would be evenly distributed onto the structure below.

Neither of those things are true. Therefore it isn't impossible for the upper block to accelerate somewhat slower than freefall as it begins to fall.

The Core and perimeter columns in the Towers got stronger the lower you went and were stone cold and rock hard from at least the 80th floor to the ground.

 

[triforcharity]

The Core and perimeter columns in the Towers got stronger the lower you went and were stone cold and rock hard from at least the 80th floor to the ground.

Yes, but suprisingly, the connections of those columns were the same throughout.

 

[Carlos]

The Core and perimeter columns in the Towers got stronger the lower you went...

And the velocity, the kinect energy and the momentum got higher.