WTC7 and the girder walk-off between column 79 and 44

[tsig]

Originally Posted by Tony Szamboti View Post
So are you saying you think the girder between columns 44 and 79, with the flange to web stiffeners shown on drawing 9114, could have walked off its 12" wide seat at column 79 due to beam expansion from the east?

NoahFence


There was no massive fire or fires.
The column was likely whisked away to China, wasn't it?

I thought it walked off.

 

[twinstead]

I thought it walked off.

Oh no he di'int!

 

[Tony Szamboti]

There is no meaningful elastic recovery time for parts that are simply overloaded to failure. Which is exactly what happened to concrete floors and connection bolts.

Parts go sliding right thru "elastic", then thru "plastic", right into "good bye".



The "rice in the bag" model was perfectly satisfactory to make the point that Dave was trying to make: the difference between static load & dynamic load.

In the collapse, about 70% of the debris stayed within the footprint of the building & about 30% was ejected.

In the absence of the bag, about 90% of the rice would have been ejected or flowed over the sides of the scale. This would have been a much worse model than the one used.

The presence of the bag improved the demonstration over the absence of the bag.

tk

PS. If Dave were to bother to improve his model, and he didn't care about damaging his scale, he could replace the rice with nuts, bolt & nails, throw in some small stones for concrete, maybe even some small pieces of plaster, put it all in a potato sack with holes big enough to let about 30% of the contents slide thru on impact.

But that was not his purpose. His purpose was to demonstrate the difference between static & dynamic loads.

He did that just fine.

The use of the bag invalidated Dave Thomas' test to see if loose rubble produces a dynamic load, since it does cause the loose items to act in unison which wouldn't occur otherwise.

The legitimate way to do the test is

1. Put sides up around the scale using something like cardboard or plastic panels to prevent any of the material from missing the scale.

2. Pour a known mass of the loose material on the scale from a given height and record the maximum weight (force) registered during the pour.

3. Repeat step 2 with a solid metal item of the same mass and compare.

 

[carlitos]

Lol. "if"

 

[LSSBB]

I thought it walked off.

That was the girder.

 

[tfk]

The use of the bag invalidated Dave Thomas' test to see if loose rubble produces a dynamic load ...

And this is exactly why I've said in the past that, in spite of the fact that some university handed you a diploma after completing 4 years of coursework, I have a serious problem calling you a mechanical engineer.

The one, the only, reason for doing that experiment is to demonstrate the difference between static & dynamic load to people who have absolutely no background, experience with, or feel for mechanics.

Being in the set of people "who have absolutely no background, experience with or feel for mechanics" excludes one (IMHO) from the set of "mechanical engineers".

As Carlitos says, there is no "if" here.

Each individual component has the capacity to deliver a far higher dynamic load than its static weight. No "ifs" allowed.

The STATIC load that the compacted layer can deliver can be determined by looking at the inverse problem: how much force would it take a compactor (i.e., a mechanical crusher) to crush an equivalent structure to its equivalent compaction factor. (Plus the structure's static weight, of course.)

As the debris compacts in the zone between the upper & lower portions, it will deliver its impact more & more like a solid, single structure.

It's pretty clear to me that the amount of compaction that is required for the upper falling mass to destroy the lower, massively weakened upper floor is very small. And one can get an approximation for that number (averaged), from the actual descent acceleration of the upper structure, as about 1/3rd the weight of the upper structure.

I believe that the vast majority of the compaction of the debris happened, not during the descent, but when the debris was finally constrained by the ground, and the upper descending block could finally deliver all of its dynamic load onto the as yet lightly compressed zone, turning it into the highly compressed material seen after the fact.

 

[tfk]

That was the girder.

I think tsig made a funny...

For my money, I wish it was the girdle that was whisked away.
Maybe another glass of wine.

Ouch.
Showing my age.
You NEVER see those anymore...

 

[ozeco41]

Lol. "if"

and lol 'pour'

There's no 'if' but the the rate of 'pouring' will have a large influence on the spread of the dynamic load impulse.

 

[LSSBB]

I think tsig made a funny...

I know. Next time I post a with my comment.

 

[Justin39640]

The use of the bag invalidated Dave Thomas' test to see if loose rubble produces a dynamic load, since it does cause the loose items to act in unison which wouldn't occur otherwise.

The legitimate way to do the test is

1. Put sides up around the scale using something like cardboard or plastic panels to prevent any of the material from missing the scale.

2. Pour a known mass of the loose material on the scale from a given height and record the maximum weight (force) registered during the pour.

3. Repeat step 2 with a solid metal item of the same mass and compare.

I'd suggest a "dump" more than a controlled pour. Rubble will hit much harder than a static load. Ever watch a dump truck or pickup get loaded with sand from a payloader? I've seen suspensions and tires get blown out from a load (that would be a rated load for the truck) being dumped into the bed.

Geez, how'd that happen Ton????

 

[Tony Szamboti]

And this is exactly why I've said in the past that, in spite of the fact that some university handed you a diploma after completing 4 years of coursework, I have a serious problem calling you a mechanical engineer.

The one, the only, reason for doing that experiment is to demonstrate the difference between static & dynamic load to people who have absolutely no background, experience with, or feel for mechanics.

Being in the set of people "who have absolutely no background, experience with or feel for mechanics" excludes one (IMHO) from the set of "mechanical engineers".

As Carlitos says, there is no "if" here.

Each individual component will has the capacity to deliver a far higher dynamic load than its static weight. No "ifs" allowed.

The STATIC load that the compacted layer can deliver can be determined by looking at the inverse problem: how much force would it take a compactor (i.e., a mechanical crusher) to crush an equivalent structure to its equivalent compaction factor. (Plus the structure's static weight, of course.)

As the debris compacts in the zone between the upper & lower portions, it will deliver its impact more & more like a solid, single structure.

It's pretty clear to me that the amount of compaction that is required for the upper falling mass to destroy the lower, massively weakened upper floor is very small. And one can get an approximation for that number (averaged), from the actual descent acceleration of the upper structure, as about 1/3rd the weight of the upper structure.

I believe that the vast majority of the compaction of the debris happened, not during the descent, but when the debris was finally constrained by the ground, and the upper descending block could finally deliver all of its dynamic load onto the as yet lightly compressed zone, turning it into the highly compressed material seen after the fact.

I don't think much of your skills as an engineer either.

Aside from that, there can't be a dynamic load without a deceleration. You invalidated all of your comments by just combining the fact that it was continuously accelerating at 2/3rds of the rate of gravity with your claim that there was a dynamic load.

The experiment I discussed will show there is little to no dynamic load generated relative to the static weight of the overall mass when the loose items are poured on the scale.

 

[Justin39640]

and lol 'pour'

There's no 'if' but the the rate of 'pouring' will have a large influence on the spread of the dynamic load impulse.

Absolutely. In the example I gave above, the blown out leaf springs and shocks were because the operator just dumped the load as fast as he could. Good operators use a slow controlled pour to avoid damage.

 

[Justin39640]

I don't think much of your skills as an engineer either.

Aside from that, there can't be a dynamic load without a deceleration. You invalidated all of your comments by just combining the fact that it was continuously accelerating at 2/3rds of the rate of gravity with your claim that there was a dynamic load.

The experiment I discussed will show there is little to no dynamic load generated relative to the static weight of the overall mass when the loose items are poured on the scale.

That's completely wrong and insane.

 

[tfk]

I don't think much of your skills as an engineer either.

Somehow, I am perfectly comfortable with that.

No, "comfortable" doesn't go quite far enough.

Somehow, I am perfectly happy with that.

That's better.

Aside from that, there can't be a dynamic load without a deceleration.

There is a deceleration.

The deceleration is the 1/3G to which the upper block does not accelerate.

That is the result of an upward force, aka "a load".

It is equivalent to the maximum force that the heavily damaged lower structure can deliver to the upper block before those components fracture.

You invalidated all of your comments by just combining the fact that it was continuously accelerating at 2/3rds of the rate of gravity with your claim that there was a dynamic load.

Sure thing, Tony.

And a stationary object is accelerating at 32 ft/sec²...

The experiment I discussed will show there is little to no dynamic load generated relative to the static weight of the overall mass when the loose items are poured on the scale.

Just out of curiosity, please tell us, what is the magic mass, below which an object will not exert a dynamic load and above which it will exert a dynamic load?

We've already established that you think that it is "greater than the mass of a grain of rice".

We've also established that you think that it is less than the mass of the upper blocks of the WTC.

Is it 10 grams? 100 gms? 1000 gm? 100 kg???

At what mass will the fundamental laws of physics change?

 

[ozeco41]

Absolutely. In the example I gave above, the blown out leaf springs and shocks were because the operator just dumped the load as fast as he could. Good operators use a slow controlled pour to avoid damage.

Yes.

For my previous post I thought about posting the reality of 'dynamic load' becoming asymptotic to zero as the rate of pour decreases^##. Theoretically but not in practice limited at the extreme by how small the individual particles are. I decided not to post what should be bleeding obvious to any engineer/physicist.

Tony is still relying on ignoring the rate of pour factor but implicitly he is pouring 'very slowly'. If we remove a couple of inferences:

...The experiment I discussed will show there is little to no dynamic load generated relative to the static weight of the overall mass when the small loose items are poured on the scale slowly.

(My inserted words in blue.) However doing that probably makes it too obvious that we are faced with an apples and oranges false comparison.



Edit: PS ^## Ooops. Crossed in posting with tfk - he has addressed the same issue(s) from a different perspective.

 

[Justin39640]

Yes.

For my previous post I thought about posting the reality of 'dynamic load' becoming asymptotic to zero as the rate of pour decreases^##. Theoretically but not in practice limited at the extreme by how small the individual particles are. I decided not to post what should be bleeding obvious to any engineer/physicist.

Tony is still relying on ignoring the rate of pour factor but implicitly he is pouring 'very slowly'. If we remove a couple of inferences:
(My inserted words in blue.) However doing that probably makes it too obvious that we are faced with an apples and oranges false comparison.



Edit: PS ^## Ooops. Crossed in posting with tfk - he has addressed the same issue(s) from a different perspective.

Indeed it is. Seeing the top part of the towers first impacted the lower parts relatively intact, I would think Dave's experiment is completely valid. Drizzling sand onto a scale... not so much.

 

[ozeco41]

Indeed it is. Seeing the top part of the towers first impacted the lower parts relatively intact, I would think Dave's experiment is completely valid. Drizzling sand onto a scale... not so much.

I understand where you are coming from. I prefer to stay clear of abstract models when trying to explain real world WTC events on 9/11. Both 'sides' so often get confused as to how far the abstract model can be taken - often drifting too far into territory where explaining the real collapse is more benefit that misapplying abstractions.

Dare I say 'Missing Jolt'

 

[Tony Szamboti]

There is a deceleration.

The deceleration is the 1/3G to which the upper block does not accelerate.

That is the result of an upward force, aka "a load".

It is equivalent to the maximum force that the heavily damaged lower structure can deliver to the upper block before those components fracture.

No, a deceleration requires a loss of velocity and there was no loss of velocity. Constant acceleration at values less than g are due to resistance which is less than the static load.

Just out of curiosity, please tell us, what is the magic mass, below which an object will not exert a dynamic load and above which it will exert a dynamic load?

We've already established that you think that it is "greater than the mass of a grain of rice".

We've also established that you think that it is less than the mass of the upper blocks of the WTC.

Is it 10 grams? 100 gms? 1000 gm? 100 kg???

At what mass will the fundamental laws of physics change?

The experiment I described was actually relative. You can use any mass you want but you will also need a scale to match it and a way to handle the loose rubble.

Here is something anyone can do.

Take a 5 lb. bag of sugar or 2 lb. box of rice and put some sides around a scale with ounce graduations with at least a 10 lb capacity, and pour the sugar or rice from the same height as what Dave Thomas dropped his bag of rice from. I'll bet you don't see much more than 5 lbs. for the sugar or 2 lbs. for the rice if any at all.

 

[carlitos]

Congratulations to Tony for disproving shotguns and avalanches.

 

[ozeco41]

Congratulations to Tony for disproving shotguns and avalanches.

Nah....

...he has only disproved shotguns using slow burning cartridges OR hand poured avalanches.