An email from a Conspiracy theorist, and I have no idea how

[T.A.M.]

technically, Heiwa has not proven he is an engineer, but nor has it been proven he is not. I am merely speculating that he is not based on his running from this thread when the tough questions were asked, and his lack of knowledge etc...in his posts...

TAM

 

[Heiwa]

I am not sure either of your assumptions here (preimeter columns and core unaffected by heat) are valid. In the heat transfer analysis the temp of the perimeter columns does not equal the outside air temp. Convection is just not that efficient. As to the core, I think it is fairly safe to assume that those columns are also not at room temperature.


One might have to model the welds or bolted connections on the beams. Add in expansion due to heat. As to the time parameter, it could be heat transfer effects (which have a time component) or stress relaxation which also has a time component and is greatly effected by temperature. Also, all beams are not loaded equally after the impact so some may heva higher loads than others and fail at different times, thus the time factor again shows up.



And you have performed the FEA showing this or are you just making educated guesses?

Lurker

Re heat I assume it is <600°C locally and <300°C generally so it would not affect the material properties too much; the heat will assist deformation.

One difficulty is to model the floor trusses. The lower flange is a steel bar, the 'web' is also steel bars, but the upper flange is a steel plate + concrete poured on it. Thus the upper flange sandwich of the trusses is quite strong and if it it continuously connected to the perimeter and core walls/columns all around, it can hardly detach due to heat. So the floors may deform - sag - when the lower flange heats up (the span is quite long) but even so it is unlikely that the connections to the walls will burst and then the floors would still support the columns = no collapse.

The floor sag is also limited to the free height of the floors, i.e. new support/contact points will develop.

I use a CASA Gifts software of limited capability just to get a feel of the problem. According my opinion the heat could contribute to local deformations, e.g. the east wall, but hardly to global collapse.

 

[Gravy]

One difficulty is to model the floor trusses. The lower flange is a steel bar, the 'web' is also steel bars, but the upper flange is a steel plate + concrete poured on it. Thus the upper flange sandwich of the trusses is quite strong and if it it continuously connected to the perimeter and core walls/columns all around, it can hardly detach due to heat. So the floors may deform - sag - when the lower flange heats up (the span is quite long) but even so it is unlikely that the connections to the walls will burst and then the floors would still support the columns = no collapse.

Since you came back, I'll also come back.

Heiwa. Pay close attention.

You
still
have
no
idea
what
NIST's
explanation
of
the
collapses
is.

Since you refuse to read the NIST reports, will you at least take a few goddamned minutes and read their short "Answers to frequently asked questions?"

Will you?

Jesus Christ, what deliberately ignorant children the 9/11 deniers are.

 

[Belz...]

Re heat I assume it is <600°C locally and <300°C generally so it would not affect the material properties too much; the heat will assist deformation.

Why stop there ? Why not simply assume it's room temperature ?

 

[Lurker]

Re heat I assume it is <600°C locally and <300°C generally so it would not affect the material properties too much; the heat will assist deformation.

Well, there is one of your first problems there. You need more precise answers than this to actually perform the heat trasnfer analysis. To know the temperature distribution in the WTC, clearly the outer members would either be at a known temp or at a calculated temp from the FEA. The fact that you have no idea reveals that you did not perform an FEA of the structure. Or at least, not a coupled heat transfer/strucural analysis.

... but even so it is unlikely that the connections to the walls will burst and then the floors would still support the columns = no collapse.

I am not sure people are claiming the connections burst but that the floors pulled the outer walls in which reduced the structural capacity of those columns.

I use a CASA Gifts software of limited capability just to get a feel of the problem. According my opinion the heat could contribute to local deformations, e.g. the east wall, but hardly to global collapse.

The question is whether the combination of heat AND loss of structural integrity due to the plane crash was enough to cause the collape. Your opinion is noted but I see you have failed to back it up with anything more than continued opinion. Why not put your FEA model up on a FTP site so we can take a look?

Lurker

 

[Lurker]

Heiwa:

I will make a simple analogy of what happened. (Correct me if I am wrong)

1. Imagine a floor is held up by 80 columns.

2. A plane hits them and takes out ro severely damages 25 of them. Many remaining columns have the fireproofing damaged and/or removed from the impact.

3. The load of each remaining column increases by a minimum of 45% as the load redistributes to the remaining columns (we ignore bending forces, eccentrically loaded columns, and assume the load is distributed evenly which it would not be)

4. As the fires rage on, the temperature rises. Since every engineer knows that the modulus is a function of temperature, the strength of the materials is reduced dramatically. Also, steel and concrete elongate under the high temperature.

5. Floors sag, bending columns further reducing the structural capacity.

5. At some point, enough columns fail such that there is catastrophic and complete failure. Steel fails very quickly, it is not a ductile failure.

Hope this helps you plot out the theory.

Lurker

 

[Heiwa]

Well, there is one of your first problems there. You need more precise answers than this to actually perform the heat trasnfer analysis. To know the temperature distribution in the WTC, clearly the outer members would either be at a known temp or at a calculated temp from the FEA. The fact that you have no idea reveals that you did not perform an FEA of the structure. Or at least, not a coupled heat transfer/strucural analysis.


I am not sure people are claiming the connections burst but that the floors pulled the outer walls in which reduced the structural capacity of those columns.



The question is whether the combination of heat AND loss of structural integrity due to the plane crash was enough to cause the collape. Your opinion is noted but I see you have failed to back it up with anything more than continued opinion. Why not put your FEA model up on a FTP site so we can take a look?

Lurker

I am not doing a heat transfer analysis. I am doing a simple structural analysis at a given time with certain assumptions of the parts/members, which is only valid given the input being valid.

In my view - the floor/truss with it continuous top flange (thin steel plate/concrete) connected to the walls is very strong even when sagging. All the trusses are connected via the top flange.

Somebody asked me if I had read the NIST reports. I skimmed the first parts and concentrated on section 1-6D about the structural analysis. Unfortunately there are five authors so you do not know who has done/written what. So if you ask they can always refer to another.

Better would have been to ask one person only to analyze WTC1 and another WTC2. Now five persons analyse two different accidents and it becomes messy, e.g. fig. 5-3 on p 315. The writers mix up the two towers!

Re temperatures inside the WTC2, e.g. fig A-10, p. 342 is quite good. The core pillars are quite cool! And the perimeter columns are in fresh air so should also be cool! Max heat is apparently in the northeast corner on floor 82, etc. and you wonder why? It is not clear from any photos, etc. I doubt very much that info. How did they establish it?

The floor/truss connections to the columns are very simple. They cannot transfer any bending! Only axial forces. So even if the floor is sagging it transfers axial forces, etc. It is suggested that the sagging floor pulls in the perimeter columns but I doubt that. The vertical load on the floor is too small (20 kgs/m²). No way that a locally sagging floor will pull in all the perimeter columns. Etc. ,etc.

 

[Heiwa]

Heiwa:

I will make a simple analogy of what happened. (Correct me if I am wrong)

1. Imagine a floor is held up by 80 columns.

2. A plane hits them and takes out ro severely damages 25 of them. Many remaining columns have the fireproofing damaged and/or removed from the impact.

3. The load of each remaining column increases by a minimum of 45% as the load redistributes to the remaining columns (we ignore bending forces, eccentrically loaded columns, and assume the load is distributed evenly which it would not be)

4. As the fires rage on, the temperature rises. Since every engineer knows that the modulus is a function of temperature, the strength of the materials is reduced dramatically. Also, steel and concrete elongate under the high temperature.

5. Floors sag, bending columns further reducing the structural capacity.

5. At some point, enough columns fail such that there is catastrophic and complete failure. Steel fails very quickly, it is not a ductile failure.

Hope this helps you plot out the theory.

Lurker

I like simplifications.

1. Say it is 360 perimeter columns and 47 core columns that hold up a floor. The columns are interconnected at the floor by some horizontal bracing.

2. A plane hits them and damages 40 perimeter columns on the south side and 2 perimeter columns on the north side. All windows are blown out.

3. The load on the remaining columns increases marginally and the structure stands.

4. The temperature rises inside the building due to fire

5. The floor sags due heat. But the load on the floor is minimal (20 kgs/m²) and its own weight very small too and its connection to the column is very simple - it can only transfer axial loads but no bending moments.

5a. The axial load of the floor pulling the perimeter column inward is negligible. The perimeter column would not deform due to that.

5b. The fire/heat is getting smaller.

6. So no remaining perimeter column will suddenly fail.

 

[The Almond]

I like simplifications.

1. Say it is 360 perimeter columns and 47 core columns that hold up a floor. The columns are interconnected at the floor by some horizontal bracing.

2. A plane hits them and damages 40 perimeter columns on the south side and 2 perimeter columns on the north side. All windows are blown out.

I can agree with 1 and 2.

3. The load on the remaining columns increases marginally and the structure stands.

The load on the remaining columns increases by 25% in WTC1 (east and west walls) and 24% in WTC 2 (east wall). The load on the core decreases because the remaining top sections cause an eccentric loading.

4. The temperature rises inside the building due to fire

Changing the modulus of elasticity of the columns affected by the heat, thereby inducing plastic creep and strain deformations.

5. The floor sags due heat. But the load on the floor is minimal (20 kgs/m²) and its own weight very small too and its connection to the column is very simple - it can only transfer axial loads but no bending moments.

I was wondering where this floor load value came from. 20 kg/m^2 sounds way too low for a furniture load. The lightweight concrete in the floor was 120 lb/sq ft which translates to about 600 kg/m^2. At a depth of 5 inches, that's a floor weight of 76.2 kg/m.

5a. The axial load of the floor pulling the perimeter column inward is negligible. The perimeter column would not deform due to that.

The pull in forces, as described by NIST were 5 kips for WTC1. At elevated temperatures, this is quite sufficient to cause bowing of the exterior columns as shown in the photographic evidence.

5b. The fire/heat is getting smaller.

Irrelevant. What is at issue are the temperatures of the steel columns, the loads and the pull in forces, not the change in heat.

6. So no remaining perimeter column will suddenly fail.

These 6 points are an exceedingly poor example of an engineering analysis.

 

[Heiwa]

I can agree with 1 and 2.

The load on the remaining columns increases by 25% in WTC1 (east and west walls) and 24% in WTC 2 (east wall). The load on the core decreases because the remaining top sections cause an eccentric loading.

Changing the modulus of elasticity of the columns affected by the heat, thereby inducing plastic creep and strain deformations.

I was wondering where this floor load value came from. 20 kg/m^2 sounds way too low for a furniture load. The lightweight concrete in the floor was 120 lb/sq ft which translates to about 600 kg/m^2. At a depth of 5 inches, that's a floor weight of 76.2 kg/m.

The pull in forces, as described by NIST were 5 kips for WTC1. At elevated temperatures, this is quite sufficient to cause bowing of the exterior columns as shown in the photographic evidence.

Irrelevant. What is at issue are the temperatures of the steel columns, the loads and the pull in forces, not the change in heat.

These 6 points are an exceedingly poor example of an engineering analysis.

Thanks for agreeing with 1 and 2.

But then you are wrong.

Due to the design of the floor connections to the perimeter and core columns, the floors cannot transfer any vertical loads from the perimeter columns to the core columns during any alleged load re-distribution due to heating the floors! What does this mean for WTC2?

According NIST the east wall buckled at the damaged floors around floor 82 and there was load redistribution, i.e. the weight of the undamaged section above carried by the east wall was transferred to the north and south walls and the core columns.

However - no load could be transferred from the perimeter columns to the core via the floors. The trusses cannot transfer any big loads as shear and will not participate in the load re-distribution! (The only load on the floor truss transferred to the columns as shear is the weight of furniture, etc. (20 kgs/m² according NIST) on the truss and its own weight through a very small connection ot the truss to the column.

The load on the east wall can only be transferred to the north and south walls via the horizontal bracings keeping the perimeter together sideways at every floor. Either they manage to do that or they shear off ... like the floor connections of the east wall ... and the whole east wall above the buckled section would fall down to the ground! The east wall below the damaged section and the whole tower below the damaged section would stand.

Maybe some parts of the north and south walls would also fall down, but the west wall and the core evidently should stand! Quite basic, actually. That's why no steel skyscraper has ever globally collapsed. Local collapse of some areas for various reasons, yes.

Compare the building in Oklahoma city, where a home made bomb removed the perimeter columns of the front wall at ground level! The whole front wall fell down ... but the remainder of the building remained standing. Reason - the floors did not re-distribute load to the other side of the building.

So the NIST proposal (without any evidence) that global collapse of the whole tower ensues when the east wall first buckles and then collapses is wrong. Only the east wall above the damaged east wall section would fall down, i.e. only a local collapse would occur. The core and the west wall should be standing and probably most of the south and north walls. And the whole tower below the damaged floors.

All proposals of the heat weaking the structure all around and the core in the damaged area is just nonsense to confuse local collapse with global collapse.

NIST should be asked why not only local collapse ensued due to some local failures, i.e. only the east wall above the damaged area falling down.

But local collapse did not ensue. Suddenly the whole building explodes from the damaged area down to the bottom. What we see on all videos is not global collapse ... that should take much longer time ... but controlled demolition. No doubt about it.

 

[twinstead]

But local collapse did not ensue. Suddenly the whole building explodes from the damaged area down to the bottom. What we see on all videos is not global collapse ... that should take much longer time ... but controlled demolition. No doubt about it.

What do you have to say to the many experts who have studied the collapse and disagree with you?

You realize there's a bunch of them, right?

 

[Dave Rogers]

However - no load could be transferred from the perimeter columns to the core via the floors. The trusses cannot transfer any big loads as shear and will not participate in the load re-distribution! (The only load on the floor truss transferred to the columns as shear is the weight of furniture, etc. (20 kgs/m² according NIST) on the truss and its own weight through a very small connection ot the truss to the column.

Aren't you forgetting the hat truss?

Dave

 

[Crungy]

Aren't you forgetting the hat truss?

Dave

He's only taking into account the "tin hat" truss.....

 

[The Almond]

Thanks for agreeing with 1 and 2.

I have no problem with fact, no matter who says it.

But then you are wrong.

This, from the guy who thinks a 25% increase in column load is marginal.

Due to the design of the floor connections to the perimeter and core columns, the floors cannot transfer any vertical loads from the perimeter columns to the core columns during any alleged load re-distribution due to heating the floors! What does this mean for WTC2?

This means that you have completely misrepresented NIST's mechanism for load distribution. And you've supported your contention without reference, evidence or calculation.

NIST clearly states on page 297 of NCSTAR 1-6 the actual load transfer mechanisms. It does not rely entirely on the floors to establish load transfer, and it includes an analysis of the hat truss load transfer mechanism (a point that you have conveniently omitted).

According NIST the east wall buckled at the damaged floors around floor 82 and there was load redistribution, i.e. the weight of the undamaged section above carried by the east wall was transferred to the north and south walls and the core columns.

You appear to be referencing 1-6 page 307. It would be helpful for other readers if you would reference your claims, especially when you're summarizing what you think NIST wrote.

However - no load could be transferred from the perimeter columns to the core via the floors.

While this may be true, the load could be transferred via the hat truss, spandrels and other load transfer mechanisms. You are using an incredibly dishonest half truth here.

The trusses cannot transfer any big loads as shear and will not participate in the load re-distribution! (The only load on the floor truss transferred to the columns as shear is the weight of furniture, etc. (20 kgs/m² according NIST) on the truss and its own weight through a very small connection ot the truss to the column.

References? Calculations?

The load on the east wall can only be transferred to the north and south walls via the horizontal bracings keeping the perimeter together sideways at every floor. Either they manage to do that or they shear off ... like the floor connections of the east wall ... and the whole east wall above the buckled section would fall down to the ground! The east wall below the damaged section and the whole tower below the damaged section would stand.

References? Calculations?

Maybe some parts of the north and south walls would also fall down, but the west wall and the core evidently should stand! Quite basic, actually. That's why no steel skyscraper has ever globally collapsed.

Pardon me? No steel skyscraper has ever globally collapsed?

Local collapse of some areas for various reasons, yes.

Such as weakening through heat, sagging of floor trusses and so on?

Compare the building in Oklahoma city,

If I knew absolutely nothing about building design, structural analysis and basic construction, I would compare the WTC towers to the Oklahoma city building. The two structures are not comparable.

where a home made bomb removed the perimeter columns of the front wall at ground level!

I'm missing the part where an airplane smashes into the OK city building.

The whole front wall fell down ... but the remainder of the building remained standing. Reason - the floors did not re-distribute load to the other side of the building.

WHERE DID THE LOAD GO????

So the NIST proposal (without any evidence)

I think you're confusing the NCSTAR with everything you've written in this post.

that global collapse of the whole tower ensues when the east wall first buckles and then collapses is wrong.

I would love to see your analysis, your calculations, your references, your published documents, etc., to prove this.

Only the east wall above the damaged east wall section would fall down,

See above.

i.e. only a local collapse would occur. The core and the west wall should be standing and probably most of the south and north walls. And the whole tower below the damaged floors.

I'm sorry to sound like a broken record, but you're simply restating your original opinion without evidence, calculations or references.

All proposals of the heat weaking the structure all around and the core in the damaged area is just nonsense to confuse local collapse with global collapse.

Your opinion does not matter in this debate.

NIST should be asked why not only local collapse ensued due to some local failures, i.e. only the east wall above the damaged area falling down.

They would probably tell you to look at the extensive FEA they completed, along with the calculations about load distribution, column deflection, and their comprehensive thermodynamic analysis of the fires. Then they would probably ask you why WTC 2 was leaning 8 degrees off plumb before collapse if only local failures were to blame.

But local collapse did not ensue. Suddenly the whole building explodes from the damaged area down to the bottom. What we see on all videos is not global collapse ... that should take much longer time ... but controlled demolition. No doubt about it.

You continue to restate your opinion as fact. That will not work here.

 

[Heiwa]

While this may be true, the load could be transferred via the hat truss, spandrels and other load transfer mechanisms. You are using an incredibly dishonest half truth here.

Good that you agree that the floors are just hanging between the perimeter and core columns with help of their trusses and do not contribute one jota to the global strength of the tower. They are only there to provide fire division between the floors.

This means that a sagging floor will not pull in any perimeter columns.

Actually the concrete floors with their trusses should be completely ignored in a serious analysis and we should only concentrate on members that can transfer loads between the perimeter and core columns. And as they are fully intact above the impact zone, the load distribution is very effective and no column will overload in the impact zone if we, e.g. remove the east wall completely. It is called redundancy.

 

[T.A.M.]

Good that you agree that the floors are just hanging between the perimeter and core columns with help of their trusses and do not contribute one jota to the global strength of the tower. They are only there to provide fire division between the floors.

This means that a sagging floor will not pull in any perimeter columns.

Actually the concrete floors with their trusses should be completely ignored in a serious analysis and we should only concentrate on members that can transfer loads between the perimeter and core columns. And as they are fully intact above the impact zone, the load distribution is very effective and no column will overload in the impact zone if we, e.g. remove the east wall completely. It is called redundancy.

You have got to be kidding. So if I have a string tied to a pole, unless that string contributes to helping the pole remain erect, I cannot pull on the string, and pull the pole to one side???

TAM

 

[twinstead]

Again, Heiwa, exactly what would you say to the many experts who would disagree with you? Would they accept you as a peer and have a rousing, esoteric debate with you about insider expert structural engineering stuff, then invite you to their local watering hole to thank you and to enlighten their colleagues about your brilliant, new-found issues with the WTC that they seemed to have completely missed, or perhaps just roll their eyes and wonder just who the heck you are, anyway?

As a total layman I tend to seek out experts to explain stuff like this to me. It's critical that I only listen to people who really know what they are talking about, and perhaps also have as few ideological biases as possible.

So. Exactly why should I be listening to you?

 

[The Almond]

Good that you agree that the floors are just hanging between the perimeter and core columns with help of their trusses and do not contribute one jota to the global strength of the tower.

I said that it may be true in the hope that you might provide something other than your opinion on the matter. Until you provide such an analysis, I'm humoring you, not agreeing with you.

They are only there to provide fire division between the floors.

I'd just like to point out that the purpose of a floor is to transfer the live load (people, water and such) to the columns, which then transfer the load to the ground. Floors are not just some fire barrier, they are the active structure of a building.

This means that a sagging floor will not pull in any perimeter columns.

This statement is nonsensical.

Actually the concrete floors with their trusses should be completely ignored in a serious analysis

Have you ever done a serious forensic collapse analysis? Or perhaps you could point to one in literature where the concrete floors were ignored.

and we should only concentrate on members that can transfer loads between the perimeter and core columns.

This would be serious news to all professional engineers in the world. Perhaps you should tell them.

And as they are fully intact above the impact zone,

In the same sense that a person with an arrow in his chest is fully intact above the arrow's impact zone.

the load distribution is very effective

Opinion.

and no column will overload in the impact zone if we, e.g. remove the east wall completely. It is called redundancy.

Opinion.

Frankly Heiwa, your thesis seems to rest upon the rather untenable idea that the sagging of the floors in the WTC towers had no bearing on the collapse itself. You're asking us to accept that idea without any analysis, calculations, evidence or modeling, and despite the fact that it is central to NIST's collapse hypothesis. That's ludicrous.

 

[Newtons Bit]

Good that you agree that the floors are just hanging between the perimeter and core columns with help of their trusses and do not contribute one jota to the global strength of the tower. They are only there to provide fire division between the floors.

This means that a sagging floor will not pull in any perimeter columns.

Actually the concrete floors with their trusses should be completely ignored in a serious analysis and we should only concentrate on members that can transfer loads between the perimeter and core columns. And as they are fully intact above the impact zone, the load distribution is very effective and no column will overload in the impact zone if we, e.g. remove the east wall completely. It is called redundancy.

Wow. Let's look at a few things here. The floor slab braces the top chord of the floor trusses against lateral torsional buckling and against axial buckling. The trusses brace the columns against axial buckling. The "brace force" can be computed as approximately 1-3% of the total axial load. This means that the truss needs to be able to resist 1-3% of the axial load in the columns. If the truss is comprimised by fire, it will sag, and if it sags, it will not resist buckling of the columns. This is a very important, although BASIC concept.

The trusses will pull on the columns when the trusses are no longer able to carry the entirety of the bending moments. There is a point where the truss will begin acting more like a tension member. Instead of a truss, invision a rope connected to two columns with a point load in the middle of that rope.

There is also another important mechanics which will pull an out-of-plane force on the exterior columns, namely, the loss of interior columns. How do you think the axial load of an interior column gets redistributed to the rest of the building? Without the hat truss or any of the floor trusses, the column will just fall. The principal way for a column to resist falling is through the members that are attached to it, namely: the floor trusses. The column will fall a certain distance and the floor trusses that are connected to it will elongate (up to the rupture point) and pull the column up. Again, they will become TENSION members putting an axial out-of-plane load on the columns that they are attached to.

The floor trusses are integral to the entire mechanism which resisted the collapse from the initial plane impact. This is obvious to anyone who has spent any time doing structural engineering.

 

[Belz...]

Heiwa, maybe you should stick with non-building related work. Gardening, perhaps.