Merged Applicability of Bazant's model to the real world

[Myriad]

When my block of wood hits the ground, R and F are the same, but the block decelerates. Yes, or no?

No. If R (force of floor pushing upward on block) and F (force of gravity pulling down on the block) stayed the same magnitude as one another, the net force on the block would be zero. So by Newton's first law of motion, the block would keep going.

See the previous post, for an explanation of why and how in that case, R significantly exceeds F.

Respectfully,
Myriad

 

[cooperman]

No. If R (force of floor pushing upward on block) and F (force of gravity pulling down on the block) stayed the same magnitude as one another, the net force on the block would be zero. So by Newton's first law of motion, the block would keep going.

See the previous post, for an explanation of why and how in that case, R significantly exceeds F.

Respectfully,
Myriad

So what is R? How do you calculate it's magnitude? If a 10kg block falls under gravity and hits the floor, what will R be?

I am genuinely interested to learn. I am happy to admit I may be misunderstanding newtons law here.

Quite why RMackey feels the need to put someone on ignore because they get something wrong is beyond me.

 

[cooperman]

Yes, I see where I have gone wrong here. I have, stupidly, been assuming that F or mg is equal to the force the falling body imparts on the object it hits.

Please ignore my previous garbage.

 

[cooperman]

This has to be a simple troll.

Newton's Second Law, chum. Learn it. But not from me. You earn my coveted Ignore.

It seems I have made a fundamental error and admitted it. Why would you put someone on ignore because they dont understand collision problems and newtons laws as well as you do?

 

[ergo]

The floor is resting upon something somewhat a little bit larger than the brick. It is not a cube

And a building is not resting on the earth? What exactly are you saying here?

Try dropping a brick onto a piece of tissue paper strung above ground between two sticks and ask yourself what happens. Does the tissue paper cause the brick to decelerate ?

Are you suggesting that the floors of the WTC are like tissue paper? And the descending block is like a brick? Does the descending block also have floors like tissue paper?

I suggest the entire discussion is split out. It's ridiculous.

It has been ridiculous for a very long time.

 

[ergo]

Quite why RMackey feels the need to put someone on ignore because they get something wrong is beyond me.

Don't worry, he's not really ignoring you.

 

[cooperman]

Don't worry, he's not really ignoring you.

I guessed as much but it is a very strange way to react to a layman like me making a mistake regarding newtons laws. I gather that Mackey is a rocket scientist and I have never spoken to him.

If I see someone less knowledgable than me in a particular field is getting something wrong then my instinct is to help them learn not ignore them.

All respect to Myriad here. I must have sounded like a completely thick troll and yet he still continued to try and point out my error.

I must apologise for my obtuseness to myriad. I really thought I was right.

Well, you live and learn.

 

[beachnut]

No, he's an engineer. What are you?

For 911 issues he is an engineer with a CD delusion and paranoid conspiracy theories. Not that you need to be an engineer to understand Bazant's model, but you need to comprehend and understand the model to keep from being off topic in a thread which you can only expose your ignorance and fail. Carry on. I bet you can't be on topic in this thread.

Bazant's model is applicable to the real world and if you can't grasp that, then it is not a surprise you share the moronic CD fantasy with Tony the engineer who can't publish his work because it is nonsense.

 

[ergo]

Your error is a completely unjustified assumption that the two forces that are actually acting on the falling object, the force of gravity and the force the object it hits imparts on it, must be equal. They do not represent a pair of equal and opposite forces.

I don't think you've understood the argument, or Newton's Third Law. The law states that the impact force of the descending block will be met by the resisting block, just like a car driving into a brick wall. That impact will be shared equally between the two blocks, but will affect them differently because they are not equal in mass.

Thirty storeys hitting 80 storeys is, to the upper block, like 80 storeys hitting 30. That is Newton's third law.

That's why the "net force equals zero" argument is invalid.

I don't believe this is the argument being made.

 

[Grizzly Bear]

<snipped>

Kudos for spotting the mistakes and admitting it at least in this discussion...

As a an off the record comment some of us have been in these sorts of debates for years now and have had many experiences where people have made responses just for the sake of trolling. The reaction to that's pretty understandable given that it happens so often in these forums. But occasionally it's not... after so many experiences with that it's not always readily apparent.

 

[Mel Odious]

I guessed as much but it is a very strange way to react to a layman like me making a mistake regarding newtons laws. I gather that Mackey is a rocket scientist and I have never spoken to him.

If I see someone less knowledgable than me in a particular field is getting something wrong then my instinct is to help them learn not ignore them.

All respect to Myriad here. I must have sounded like a completely thick troll and yet he still continued to try and point out my error.

I must apologise for my obtuseness to myriad. I really thought I was right.

Well, you live and learn.

Now, this is the sort of thing I'd like to see more of. Someone actually takes the time to listen to someone knowledgeable offer a critique of their argument, and then frankly admits the error when they realize they were wrong.

Bravo, Cooperman, you deserve a round of applause.

 

[ergo]

...except that Myriad's explanation is incorrect.

 

[cooperman]

Kudos for spotting the mistakes and admitting it at least in this discussion...

As a an off the record comment some of us have been in these sorts of debates for years now and have had many experiences where people have made responses just for the sake of trolling. The reaction to that's pretty understandable given that it happens so often in these forums. But occasionally it's not... after so many experiences with that it's not always readily apparent.

It is a rather embarassing error but, as you've seen, I will admit when I am wrong.

In my defence I will submit that I have not dealt with newtons laws and collision problems for 20 years and even that was only at high school level.

 

[cooperman]

...except that Myriad's explanation is incorrect.

To be fair, myriad was right that the R force must be greater to cause a deceleration. It must be by newtons second law.

 

[ergo]

Cooperman, I don't think you're wrong. We're talking about how the impact force is shared here, not about gravity versus normal force.

 

[ergo]

To be fair, myriad was right that the R force must be greater to cause a deceleration. It must be by newtons first law.

And it is. Obviously.

 

[cooperman]

Cooperman, I don't think you're wrong. We're talking about how the impact force is shared here, not about gravity versus normal force.

Yes it is still, of course, correct that the upper block recieves the same force as it exerts on the lower block. That isn't in dispute. I agree with you entirely on that.

 

[cooperman]

And it is. Obviously.

Yes, it is. I agree.

 

[ergo]

Good, then. We're agreed.

Myriad still has not shown how the net force of block C exceeds the resistive force of Block A--without referring to Bazant.

 

[ozeco41]

Good, then. We're agreed.

Myriad still has not shown how the net force of block C exceeds the resistive force of Block A--without referring to Bazant.

Can we clarify the scenario please?

Are we talking about WTC1/2?
And in the global collapse stage - i.e. after the top block starts to fall?

If both those are true then:

• We can answer without reference to Bazant. In fact Bazant and Zhou is not valid because the situation has gone outside the assumptions on which the Bazant and Zhou approximation depends;
• Most of the top block columns are not in axial end for end contact with their counterpart lower portions - that is why we are outside Bazant and Zhou's assumptions. Because the top block is falling there cannot be sufficient resistance to hold up the top block and sufficient resistance requires axial end for end contact of column parts so there are insufficient (if any) columns in axial contact AND any column that did somehow get into axial contact would be subjected to massive overload and fail instantly;##AND
• The top block is falling inside the outer tube columns of the lower tower.

Now, given that situation the resistance to the top block falling comes from two main areas and some minor ones:

• The OOS floor areas of the falling top block fall mostly onto the OOS floor area of the lower tower. Initially with some "impact zone" debris between them AND later with accumulating floor debris. That falling weight is sufficient to strip the floor joists off their connections to the columns at both ends;
• The core of the top block is also falling mostly on the core of the lower tower. Since as already explained the columns are not in axial alignment the main contact top block to lower tower core is horizontal beam on horizontal beam. The beam end connections are an order of magnitude less strong than the columns designed axial load. So those beams bend and shear off.

There are other relatively minor forces - friction of descending OOS floor material and debris against core and outer tube columns is one - friction of "bent out of line column" parts - top block part sliding past and rubbing against lower tower part - is another. Plus one confused mess in the core area.

So both areas which are in contact and transfer resistance to your "Block C" provide significant resistance but far less than could be provided by the total columns acting as designed with axially applied loads.

And not only does that explanation not require reference to Bazant, it explicitly identifies that the global collapses of WTC1 and WTC2 fell outside the range of validity of the Bazant and Zhou conservative model.

## And, for those with a sense of humour/irony whatever, that situation is the point where Tony Sz looks for his jolt AND the explanation as I have presented it does not - at that stage - preclude "unnatural causes" causing the missing bits of column. That precluding of "unnatural causes" comes a fraction of a second later in the real time collapse.