Merged Applicability of Bazant's model to the real world

[ergo]

1) It's not a tree-trunk.

Nobody is saying that it is.

2) The level of forces involved are about 1000 times more than what you see in everyday physics. That's why you have to be licensed to do engineering.

You are stating that the impact force is caused by gravity alone. How does a gravity driven process become "1000 times more" than what we see in everyday gravity driven processes?

 

[GlennB]

What is obvious to eight-year-olds and other people who understand everyday physics is that a small something cannot descend through a larger something of the same material composition via gravity alone.

Oh really? Fancy a bet?

Place a pane of glass across two pieces of wood, bricks or whatever supports you fancy.

Drop half a pane of glass onto the full pane, edge-wise.

Your understanding of physics is much poorer than you think.

 

[ergo]

It's mopre like stomping grapes. The deeper they are piled, the less you have to stomp. Just the weight of the grapes on top pressing downward will crush the grapes at the bottom. (Try bringing home a five-gallon bucket of really ripe blackberries and see what happens at the bottom of your bucket.)The accumulating rubble just provided more PE which, when exceded the carrying capacity of the next floor, became KE.

If this is true, it would take a lot longer than four seconds above the speed of free fall. There would be a visibly punctuated collapse, with large portions of the building left standing.

 

[cooperman]

Oh really? Fancy a bet?

Place a pane of glass across two pieces of wood, bricks or whatever supports you fancy.

Drop half a pane of glass onto the full pane, edge-wise.

Your understanding of physics is much poorer than you think.

What if you drop the pane flat rather than on its edge?

 

[leftysergeant]

If this is true, it would take a lot longer than four seconds above the speed of free fall. There would be a visibly punctuated collapse, with large portions of the building left standing.

Look at the initiation of collapse in both towers. (It is most noticeable in the south tower because there is less smoke in the way. The sheet rock dust comes out in puffs, one floor at a time. Then the perimeter columns start unzipping. This accelerates it all a bit. Don't look for clunkity-clunk. It's moree whamwhamwhamwhamwham of slightly less than instantaneous transfer on momentum, and it gets faster because there is also compressed air as well as solid rubble pressing downward.

 

[ergo]

Oh really? Fancy a bet?

Place a pane of glass across two pieces of wood, bricks or whatever supports you fancy.

Drop half a pane of glass onto the full pane, edge-wise.

Your understanding of physics is much poorer than you think.

This is not an example. A proper comparison would be dropping the half pane onto the other pane, both of them edge-wise, or both of them flat.

I've come across several bizarre attempts on the part of bedunkers to find some example in nature or engineering in which a smaller portion of something can descend through its larger counterpart via gravity alone.

 

[GlennB]

What if you drop the pane flat rather than on its edge?

Would you like to stick to one point at a time, or are you intent on jumping around? You made an absolute statement that was wrong. Face up to it and we can take it from there.

 

[DGM]

Would you like to stick to one point at a time, or are you intent on jumping around? You made an absolute statement that was wrong. Face up to it and we can take it from there.

I don't think he knows what the point is to begin with!

 

[ergo]

No, Glenn, he's pointing out that your analogy is incorrect and therefore inapplicable.

 

[cooperman]

Would you like to stick to one point at a time, or are you intent on jumping around? You made an absolute statement that was wrong. Face up to it and we can take it from there.

Did I? I think you might be confused. Ergo made the statement. I'm cooperman.

I would appreciate an answer, What if you drop the half-pane flat?

 

[ozeco41]

What is obvious to eight-year-olds and other people who understand everyday physics is that a small something cannot descend through a larger something of the same material composition via gravity alone...

ergo that statement is not universally true. It could be partially true in relation to the WTC Twin Towers. Much of the confusion in recent posts seems to come from mixing up a variety of analogies with the reality of what happened with WTC Twin Towers on 9/11.

The Twin towers were not homogeneous blocks and the "top block" did not descend from infinite height. The reasons why the top block was able to drop through the lower tower for both of the Twin Tower collapses is outlined in my previous post:

...The reason that the resistive force was not sufficient to slow or stop the top block in the global collapse was that there was not sufficient (if any) axial loaded columns to offer the resistance. That situation was outlined in qualitative terms in my earlier post. The key point being that Bazant and Zhou's assumption of axial column loading, a conservative and valid assumption for their purposes, was not valid for WTC Twin Towers during the "global collapse".

In simple terms the falling "top block" fell inside the outer tube of columns and therefore those columns did not contribute any significant resistance. Ditto the core columns but for different reasons.

So if you think about what happened with the real WTC Towers and avoid confusing and poorly fitting analogies the reality should become clearer. The strength of the WTC towers to resist a falling top block was in the columns. The top block missed the columns. Therefore little resistance.

My earlier post at the foot of this page http://www.internationalskeptics.com/forums/showthread.php?t=184076&page=19 goes into the details in qualitative terms. Anyone who wants to can put the numbers on it if they wish.

 

[ergo]

The Twin towers were not homogeneous blocks and the "top block" did not descend from infinite height. The reasons why the top block was able to drop through the lower tower for both of the Twin Tower collapses is outlined in my previous post: In simple terms the falling "top block" fell inside the outer tube of columns and therefore those columns did not contribute any significant resistance. Ditto the core columns but for different reasons.

So if you think about what happened with the real WTC Towers and avoid confusing and poorly fitting analogies the reality should become clearer. The strength of the WTC towers to resist a falling top block was in the columns. The top block missed the columns. Therefore little resistance.

Except that this isn't in fact what happens.

 

[leftysergeant]

This is not an example. A proper comparison would be dropping the half pane onto the other pane, both of them edge-wise...

No. You are now modelling the collapse as perimeter columns crushing down perimeter columns.

...or both of them flat.

This models the floors pancaking but it is off a bit because there is little likelihood that the flors feel flat. They would have let go sooner at one end (probably the seay on the core) sooner than on the other, so they are more likely faling slaunchwise.

In a sense, it is more like hitting the next floor with an axe than with a rubber mallet.

 

[femr2]

What if you drop the half-pane flat?

It would depend upon how far you dropped it, and how fragile the glass was. It's possible that neither break, one or t'other breaks, or both break.

A more relevant analogy is to drop >12 panes onto one pane.

 

[DGM]

It would depend upon how far you dropped it, and how fragile the glass was. It's possible that neither break, one or t'other breaks, or both break.

A more relevant analogy is to drop >12 panes onto one pane.

My guess is they all break.

 

[ergo]

It would depend upon how far you dropped it, and how fragile the glass was. It's possible that neither break, one or t'other breaks, or both break.

A more relevant analogy is to drop >12 panes onto one pane.

No, a more relevant analogy is to drop 12 panes onto 90 panes.

 

[femr2]

My guess is they all break.

If you put some fairly rigid spacers in between them, round the egde, that would be more likely.

To steer towards relevance...

If each pane could only hold the static weight of, say, 8 panes without breaking...

...and one pane was attached round the egdes to some vertical supports, above the ground...

...then dropping 12 on 1 is guaranteed to break the bottom one....

...then 13 (fragmented) panes can continue dropping.

 

[femr2]

No, a more relevant analogy is to drop 12 panes onto 90 panes.

No.

Repeat my previous post 90 times, incrementing the number of dropping panes by one each time.

Done.

 

[leftysergeant]

No, a more relevant analogy is to drop 12 panes onto 90 panes.

Great, as long as there is a space between each of the lower 90. The upper 12 are supposed to be coming down more or less at once. The lower 90 break one at a time. That's the idea behind the term "pancaking."

 

[leftysergeant]

See how simple that is. Two of us caught the same error in your logic at once and started typing.