New guy here: Questions for official hypothesis

[Sizzler]

Sizzler, it looks like we may need 2 pieces of information from you so we can address this issue from the proper perspective.

1. Do you understand the basic concept of how the floors, cores, and outer columns were tied together and how they all depended on each other to keep the building standing?

2. A lot of what we need to explain is in terms of physics, and structural engineering so we need to know if you have any experience in either of these fields. Having no experience in either is fine but if that is the case we will try to use real-world examples instead of terms used in those fields.

Be warned, though, that explaining engineering concepts in non-engineering terms can be very difficult so you may keep getting explanations that lean more towards technical than generic.

I have no engineering experience.

I have 1st year university physics under my belt and then it ends there.

answers.

1. so so

2. no

 

[FactCheck]

Sorry, I'm getting lost here.

Let me get this straight and let know where I go wrong.

The connections that held the floors between the perimeter and core were weak.

No, I never said that. Please quote where I said that if you think I did and I'll correct any miscommunication on my part. In fact all the video evidence points to many of the floors still connected when the core collapsed. The core's final collapsed looked much like the WTC 7 in that the last stages of the collapse happened from the bottom.

Thus they offered very little resistance to the falling upper floors and broke. Thus falling to the next level, causing further breakage.

Forget the floors in the core. They could have all held together without progressive collapse and the core would have fallen just the same. To my knowledge no one here has said the floors in the core all collapsed first as did with the long span floors. What I said was the columns of the top section which were on their way down would have HAD to hit the floors below. If not please explain why not. And if they did, how would each core floor hold up the massive weight of the falling top sections columns?

At the same time the core the core columns failed because of lack of support when the floors broke away.

correct?

The core columns ultimate demise happened when the columns swayed unsupported. As with the perimeter columns, once you bend the columns enough they can no longer carry the weight above. The massive leverage continued the sway to one direction until it collapsed from the bottom.

I accept that although some core columns remained after the collapse, they would have failed because they were weakened and unsupported

 

[Gravy]

Sorry, I'm getting lost here.

Let me get this straight and let know where I go wrong.

The connections that held the floors between the perimeter and core were weak.

Thus they offered very little resistance to the falling upper floors and broke. Thus falling to the next level, causing further breakage.

At the same time the core the core columns failed because of lack of support when the floors broke away.

correct?

Not quite. Remember, the collapses weren't caused by pancaking. The ENTIRE top of the buildings fell on the lower portions. Not just the floors, everything: upper core columns and beams, perimeter columns, hat truss, floors, office contents, mechanical equipment, plumbing, etc.

Think about dropping an entire office building onto another. That's essentially what happened to the towers. Yes, portions of the cores stood briefly, but they were far too incomplete and too damaged to support themselves up for long.

 

[GregoryUrich]

I stand corrected. I apologize.

I accept everything about the official hypothesis/account/report/findings/etc, except the collapses of the twin towers.

This doesn't mean I accept the alternative by default.

It may be more likely that I just don't understand the physics of the failure.

That is why I am here, and not 9-11 blogger or LC blog site.

This blog is filled with lots of experts that can explain it to me.

If I continue to ask questions, it is because I still don't understand.

In the beginning of this post I had problems understanding how a progressive collapse could actually accelerate. Many people here helped me out and now I understand.

Now my next question is how the core plays into the progressive collapse.

Is this the wrong blog for me to ask such questions?

I'll try again. First the core is more succeptible to gravitational forces (and impact during collapse) because it is weaker that the exterior wall structure.

Most of the models assume that all of the impact forces go into the columns (core and exterior wall vertical members) and are distributed evenly among them because that is the most optimistic for survival of the structure. In other words, if you can shown failure with uniform distribution, then the building will fail under any other distribution. (See Bazant's simple analysis.)

When we talk about a chaotic system, that fits under the category of "any other distribution". One way of visualising this is to consider just the upper core colliding with the lower core in two cases.

1. columns impacting unevenly - as was observed, tops of the building tilted which means that the columns could not impact evenly. If the upper columns
still impacted the lower columns, bending forces would be added to compressive forces at least in the upper part. This combination is much more effective at failing the columns than only compressive forces.

2. columns missing each other entirely - this case is most likely due to displacement of the upper core caused by tilting. Now you have horizontal members impacting horizontal members. With the forces involved, these will break easily and the upper part will continue downward. After a few of these impacts, the core columns will no longer be shored (have horizontal support from beams) and are much more succeptible to buckling. Since most core columns were recovered intact (broken at the welded joints) in three floor sections, this is most likely how they failed.

As the collapse continues, this gets more chaotic and is difficult to visualize. Nonetheless, case 1 and 2 require less energy to fail the core than Bazant's assumption above.

Using Bazant's assumption:

Every column in the upper part hits the column below it in the lower part. If most the columns in the lower part fail, global collapse will ensue. One issue not usually mentioned by JREFers is that the upper columns probably failed first which makes the calculations very messy with the possible outcome of only a partial collapse. My opinion is that until we do the messy calculations, we will not know.

 

[FactCheck]

Every column in the upper part hits the column below it in the lower part. If most the columns in the lower part fail, global collapse will ensue. One issue not usually mentioned by JREFers is that the upper columns probably failed first which makes the calculations very messy with the possible outcome of only a partial collapse. My opinion is that until we do the messy calculations, we will not know.

Do you have any visual evidence of this happening? I would predict the core columns falling would pull the perimiter columns on all 4 faces. At least some windows breaking all around the building would be an indication. I see nothing like that. What I see is the building being sucked in at the impact level and only at the side which had the most office debris.

 

[Gravy]

I stand corrected. I apologize.

I accept everything about the official hypothesis/account/report/findings/etc, except the collapses of the twin towers.

This doesn't mean I accept the alternative by default.

It may be more likely that I just don't understand the physics of the failure.

That is why I am here, and not 9-11 blogger or LC blog site.

This blog is filled with lots of experts that can explain it to me.

If I continue to ask questions, it is because I still don't understand.

In the beginning of this post I had problems understanding how a progressive collapse could actually accelerate. Many people here helped me out and now I understand.

Now my next question is how the core plays into the progressive collapse.

Is this the wrong blog for me to ask such questions?

No! You should be commended for asking questions and for persisting until you understand the answers. No doubt there are many people who have the same questions but who don't speak up. At any given time, for each member logged in here there are usually two or three non-members looking on. This discussion may be very helpful to them.

 

[FramerDave]

So... are you a heterophobe?!

No, not afraid of them at all. I don't care what they do as long as they don't flaunt it in public.

 

[Sizzler]

Thanks everyone for your comments.

I'm slowly getting there.

Let me summarize and tell me if I get anything wrong.

1. All aspects of the building (core,perimeter, trusses, etc) have to be considered as a single unit because they all depend on each other for support.

2. The falling mass of the building has more energy than could be resisted by the lower floor (this includes all parts of the lower floor, core perimete, trusses, etc) so the lower floor collapsed to.

3. The resistance (loss of energy to falling part) of lower floors is less than the energy gained by gravitational forces.

4. Thus the collapse accelerated and was observed as close to free-fall.


So my next logical question is, if you guys were able to explain this to a layman like myself, why do certain engineers not accept this hypothesis.

Please treat this question fairly.

What part of the above mechanism do they not agree with?

For example:

Do they not agree with the estimated weight of the upper part and thus the KE exerted on the lower section?

Where do the truthers go wrong?

 

[danielk]

No, not afraid of them at all. I don't care what they do as long as they don't flaunt it in public.

 

[eeyore1954]

Sizzler what mechanism would you imagine could cause 50% of the mass of the lower portion of the building to fall outside of its footprint. It is reasonable to assume some of the outer walls would fall outside and in the chaotic collapse some of the material from any part of the building may fall outside of its footprint but 50%?

That's an upper bound proposed in the paper he's referring to.

This statement made me think he thought the 50% was reasonable rather than just the upper bound

Thanks Gravy.

When I watch the collapse, you are right in that very little mass escapes in the beginning.

However, later on 'a lot' falls outside of the footprint. 50% satisfies my statement, of 'a lot'.
So what is his calculated fall time with K (out) = .5

I assumed at some point it was going to be said that the collapse was too fast considering 50% of the mass "escapes"

 

[Sizzler]

This statement made me think he thought the 50% was reasonable rather than just the upper bound



I assumed at some point it was going to be said that the collapse was too fast considering 50% of the mass "escapes"

Even if 50% escapes, Bazant's paper cites this as only affecting the fall time by less than a second (if my memory is correct).

Thus it is a non issue up to 50% loss.

At first I thought the collapse speed greatly depends on the compunding of floors and thus mass.

But as Bazant show, up to 50% loss of material doesn't affect the collapse time enough to be suspicious of it.

What I was surprised to learn was that the collapse would proceed to the ground even if none of the buildings floors contributed to the weight of the falling section.

It would have been slower, but nonetheless it would continue.

 

[Gravy]

Thanks everyone for your comments.

I'm slowly getting there.

Let me summarize and tell me if I get anything wrong.

1. All aspects of the building (core,perimeter, trusses, etc) have to be considered as a single unit because they all depend on each other for support.

2. The falling mass of the building has more energy than could be resisted by the lower floor (this includes all parts of the lower floor, core perimete, trusses, etc) so the lower floor collapsed to.

3. The resistance (loss of energy to falling part) of lower floors is less than the energy gained by gravitational forces.

4. Thus the collapse accelerated and was observed as close to free-fall.


So my next logical question is, if you guys were able to explain this to a layman like myself, why do certain engineers not accept this hypothesis.

Please treat this question fairly.

What part of the above mechanism do they not agree with?

For example:

Do they not agree with the estimated weight of the upper part and thus the KE exerted on the lower section?

Where do the truthers go wrong?

I'm not aware of a single structural engineer – or anyone else – who has written a paper that claims to show that the towers should not have completely collapsed, that would pass muster with the engineers here or with the reviewers of an engineering journal.

People are free to have their opinions, but if opinions about engineering matters aren't backed by sound reasoning and calculations, I feel free to disregard them, as do the hundreds of thousands of engineers worldwide who don't accept tripe as truth.

People like Steven Jones are willing to disregard facts, logic, and their own educations and professional standards for political reasons. There will always be people like that. As with the people who falsely claimed to be 9/11 victims for financial gain, 9/11 and the subsequent U.S. wars brought out the worst in some people. It's just sad that so many people have abandoned critical thinking and held up these obvious incompetents and charlatans up as champions of "truth."

 

[GregoryUrich]

Do you have any visual evidence of this happening? I would predict the core columns falling would pull the perimiter columns on all 4 faces. At least some windows breaking all around the building would be an indication. I see nothing like that. What I see is the building being sucked in at the impact level and only at the side which had the most office debris.

That is just Bazant's simplification to prove collapse. Bazant removes all columns (both core and external) from one floor and the upper part falls with all columns hitting the columns below evenly. It is the most optimistic assumption for survival of the structure.

I was using the core only to try and explain the less optimistic scenarios.

I think you are interpreting my description as "core first". I agree that core first would cause the behavior you are describing. I don't think the core went first. It's interesting to note that, above the impact level, many floor truss seats were bent upwards, indicating the the floors were pushed upwards during collapse. If the core went first they would have been bent downwards.

 

[Sizzler]

GregoryUrich:

Maybe you can help me out.

Why do people question Bazant's paper?

Where do they think he went wrong?

 

[Calcas]

So my next logical question is, if you guys were able to explain this to a layman like myself, why do certain engineers not accept this hypothesis.

Where do the truthers go wrong?

WHY do people believe??? Even a few engineers???

Now you're getting into a WHOLE different area of psychology.

Here's a start for you but there are literally dozens of articles and books on the subject.

http://skeptically.org/logicalthreads/id15.html

 

[Hokulele]

So my next logical question is, if you guys were able to explain this to a layman like myself, why do certain engineers not accept this hypothesis.

Please treat this question fairly.

What part of the above mechanism do they not agree with?

Honestly, I haven't seen any coherent argument from any structural engineer, or architect with the appropriate background, clearly explain which points they disagree with. Most of what I have read has either had mistaken assumptions, non-technical discussion, or hand-waving dismissals of the actual observations from that day.

Did you have any engineers or a specific technical paper in mind with this question?

 

[Sizzler]

WHY do people believe??? Even a few engineers???

Now you're getting into a WHOLE different area of psychology.

Here's a start for you but there are literally dozens of articles and books on the subject.

http://skeptically.org/logicalthreads/id15.html

I mean Bazant's model specifically.

Where does he go wrong in his theory or calculations according to the experts in the truth movement.

 

[WildCat]

Where does he go wrong in his theory or calculations according to the experts in the truth movement.

The truth movement has experts? Since when, and who?

 

[Pardalis]

I accept everything about the official hypothesis/account/report/findings/etc, except the collapses of the twin towers.

Do you think there's some foul play involved with the collapse or you just can't wrap your mind around how it happened?

 

[Sizzler]

The truth movement has experts? Since when, and who?

Is it at all possible to take my question seriously? (this is a serious question)

I mean, is Bazant's theory rock solid?

Or are there areas of it that are debatable?

And if so, what is the debate?

I think this is a serious question considering the persistence of the truth movement.