Debunk This

[imstellar28]

With regards to the faster than free-fall in vacuum speed:

Beyond conjecture, nobody has given figures on either side as to whether thermite or other explosions used in building demolitions can create a low pressure environment on the detonation floors, or whether this pressure differential is enough to affect the structures fall speed.

So three things need to be investigated to refute the statements of the CTs:

1. Do any explosives used in demolitions create a low pressure environment?
2. Is the pressure difference between the falling floor and air above the structure enough to contribute significant forces on the downward movement of the floors?
3. Are there any other potential mechanisms which could contribute significant forces to the downward movement of the floors?

 

[Architect]

I was correct about the safety factors, from the NIST report figures I gave earlier in the thread, as was I in my implementation of them:

The safety factor for yielding and buckling is:
• 1.67 and 1.92 for core columns in the original design and SOP cases, and for all columns in refined NIST estimate case.
• 1.26 and 1.44 for perimeter columns in the original design and SOP case (discounting the 1/3 increase in allowable stress under wind loads).
• After reaching the yield strength, structural steel components continue to have significant reserve capacity, thus allowing for load redistribution to other components that are still in the elastic range.
• On September 11, the towers were subjected to in-service live loads, which are considered to be approximately 25 percent of the design live loads.
• On September 11, the wind loads were minimal, thus allowing significantly more reserve capacity for the exterior walls (demand on exterior columns was about 1/5 their capacity).

As I stated, after the planes impacted, the loads shifted effectively and the structure would have continued to stand as the steel has still well within its load-bearing limits due to the combination of reduced loads on 9/11 and high safety factor.

However, the potential problem with my oversimplified model, was not a misunderstanding or miscalculation of forces acting on the steel, it was that my model ignored the potential changes in geometry due to thermal expansion.

For you to refute this model, you have to show that the thermal expansion associated with a fire at X degrees was sufficient to cause deflection to the point where the steels yield strength decreased below the value of live and dead loads.

With the deepest respect, you do not appear to have grasped the points made in my post and I think you don't really follow the issues here. Can I suggest that you re-read it and tell me exactly where you disagree with my explanation, instead of simply repeating your lay interpretation of a limited part of the NIST report?

Turning to the last point, I'm afraid you'll have to be clearer. Are you suggesting that the floor trusses would not fail under floor loadings? Or are you referring to the column work?

 

[A W Smith]

stellar those safety factors assume intact structure. The columns for example. if you take out a floor between them the bracing the floor added to the columns is gone and so is the safety factor for buckling. You cant just juggle safety factor numbers around the perimeter of the building or core and and assume the reserve strength is what will hold up the building. That is simply a sophomoric oversimplification of the complexity of the buildings components involved. Those of us in the construction industry understand that.

 

[Architect]

So three things need to be investigated to refute the statements of the CTs:

1. Do any explosives used in demolitions create a low pressure environment?
2. Is the pressure difference between the falling floor and air above the structure enough to contribute significant forces on the downward movement of the floors?
3. Are there any other potential mechanisms which could contribute significant forces to the downward movement of the floors?

Although I avoid debates about thermite, I'm going to have to pick you up on your logic here.

NIST have proposed what is, from a professional perspective, a very well researched and compelling case. I have read large parts of the full report, notably the structural and fire modelling sections, because they are of both professional value to me and of personal interest. They make sense and accord with our understanding of building fabric/structural issues.

The arguments for thermite do not come anywhere close to this level of detail or understanding. Analysis is poor. There is considerable doubt as to whether thermite can indeed be used in this way.

Now the burden of proof falls upon the proposer of a theory. It is not my job to disprove it. Anything else is simply shoddy argument. And if you had been through the higher - that is university - education system then you would already know this.

So tell me, what level of expertise and experience do you bring to this table?

 

[Architect]

Right, time to deal with Safety Factors a bit more:

First of all, let's look at how the towers worked structurally.

The WTC structural frame comprised three interlinked elements; an outer loadbearing facade, the floor structure, and the inner core. These three elements acted together in order to provide overall structural stability.

The outer structure resists the force of the wind, however the external envelope also carries part (around half) of the floor loadings - the big give away is the fact that the floors rested on the exterior steelwork, which I assume you will have noticed in photographs.

Now under the effect of wind alone, columns on the windward face are in tension whilst those in the lee are in compression. In reality, however, the dead load of the structure serves to minimise the tensile loads on the windward face. However for this to work, the various parts of the structure have to be adequately tied together - the girder or space frame analogy.

Now in a normal tall building, this is carried out by columns. WTC used a different, composite system comprising lightweight trussed girders and an a reinforced concrete deck on permanent steel shuttering.

The core carried the remaining half (or so) of the gravity loads. The reason that the columns appear to be larger than the exterior facade is because they have to carry more load within a smaller cross-sectional floor (or perimeter) area.

The next thing we have to understand is what we mean by safety factor: the ratio of the breaking stress of a structure to the estimated maximum stress in ordinary use.

However it is important to understand that the loads/forces found on a complex structure such as WTC may be acting in any number of ways; for example horizontal bending or overturning moments, or gravity loads.

In the same vein, there is a difference between the safety factor of an individual part of a structure and the structure as a whole. It is perfectly possible for a steel beam to have a high factor of safety against (say) buckling under vertical (gravity) loads but a different figure for other forces.

Or another way: A beam may will have been designed to deal with certain loads, and hence (say) a transverse bending moment on a beam designed to primarily deal with vertical loadings will be a completely different kettle of fish.

To claim a figure of 600%, or 200%, or 50% as a global safety factor therefore just betrays how little you understand the subject. 600% against what? Which kind of forces? How are they acting? We can therefore only really understand the performance of the structure through global modelling.

Unlike most Cters, NIST actually do this - and not once, but three times. They look at the original design calculations, modern design calculations, and then a more forgiving global model of their own. The latter tells us that:

- Core columns in WTC typically had a Demand to Capacity Ratio (DCR) of 0.83 with around 10.6% of components exceeding design capacity under normal conditions.

- Hat Truss Columns had a typical DCR of 0.59, with 14.3% exceeding design capacity (some by DCRs of up to 1.95).

Other elements of the trusses had lower DCRs, however a truss is only as strong as the weakest member so we can set these to one side.

So where does this take us:

Well, we know that the failure was initiated by collapse of floor trusses resulting in significant buckling and eventually failure of the external load bearing envelope on the impact facades. At this point, the building was doomed to failure. The load would have been redistributed to adjacent areas and to a certain extent the hat trusses.

Now the Hat Trusses may have had up to 0.4 "spare DCR" however this is in respect of design loads. The purpose of the hat trusses was not to cantilever significant loads from envelope to core, but even if it was then it certainly wasn't capable of taking double the design load.

But even if it had been, the INTACT core only had some 0.17 "spare" DCR. that's only about 20%, and we need to bear in mind that some of the core structure already exceeded calculated capacity.

Does this debunk the alternative theory on safety factors enough for you?

Just to save you scrolling back through and hence expedite your response, Stellar.

 

[imstellar28]

I am assuming that the load bearing capability was not compromised after the plane impacts because the building was still standing, and noting that the building was very redundant. Its an assumption but you are assuming the opposite--what grounds are you basing your assumption on?

 

[WildCat]

Beyond conjecture, nobody has given figures on either side as to whether thermite or other explosions used in building demolitions

Thermite is not an explosive, and has never been used in a building demolition.

 

[Architect]

I am assuming that the load bearing capability was not compromised after the plane impacts because the building was still standing, and noting that the building was very redundant. Its an assumption but you are assuming the opposite--what grounds are you basing your assumption on?

I'd like you to think about that carefully.

We know that significant damage occured to the structural frame, most notably on the impact facades but also to the cores. This will obviously have resulted in a reduction in the overall integrity (i.e. loadbearing capacity) of the frame.

We also know from the DCR figures (amongst other things) that the level of redundancy was not particularly high. This is what we would anticipate; no-one would pay for a building with such excess amounts of structural work.

So what we had prior to fire damage was already a significant amount of weakening. You also need to remember that the elements of the structural frame act together, like a large girder, and that compromising one element may have a much wider effect on overall integrity.

Therefore no, it is not correct to assume that loadbearing capacity was essentially unaffected by the collapse and in particular I am sure you can see that at the very least one would have to question the applicability of the safety factors under such circumstances

Does that help?

 

[Minadin]

I am assuming that the load bearing capability was not compromised after the plane impacts because the building was still standing, and noting that the building was very redundant. Its an assumption but you are assuming the opposite--what grounds are you basing your assumption on?

Knowledge. Experience. Years of education at the university in the field in question. Additional years of practical application in the field.

Photographic evidence of broken exterior columns in the impact area. Photographic evidence of broken, dislodged, or sagging floor structure. Photographic evidence of raging fires.

A structure simply can't perform exactly as it was designed to do, when some parts of the structure are removed, other parts are damaged, and other parts are under unusual conditions (such as fire). The intact structure is going to experience a greater amount of load, delivered to it in a less than optimal way, because the missing / broken / damaged pieces aren't doing their jobs as they were intended anymore. The forces they were carying still exist, however. They'll simply be "re-routed" to the structure that is doing its job. Now, the intact structure is under duress because it's carrying additional loads that it wasn't designed for, coming to it in ways (directions, i.e. shear force, lateral load, torsion, bending moment, etc) that it may not be suited for. All the while, the portion of the structure that is losing strength due to the heat of the fires is transferring more and more of its load onto what structure is left, which means the problem loads only get worse as the fire rages on.

So, Architect is correct (an a heck of a lot more eloquent than I am) in his explaination as to why the "safety factors" are no longer in play.

Furthermore, I think a lot of lay people don't understand the dynamics of what is going on when a steel building is on fire. I know that before I started architecture school, I actually did think, "Ha! You can't burn down a steel / masonry building!" That incredulous belief changed completely within a few years.

Often, you will hear a conspiracy theorist say something along the lines of, "Well the fires were only X hot, so it couldn't have melted the steel." To which, of course, any knowledgable debunker / skeptic will point out that it doesn't have to melt the steel, just get hot enough to weaken it. And, that's a basically true, if rather simplistic, way of looking at it.

There are also all sorts of other factors at work in addition to the temperature of the steel members. Steel deforms due to the loads and the weakening due to heat, that is true, but it also expands as it warms up. This will cause additional stresses in other members that may or may not also be experiencing the same amount of heat. The fact that different members are different sizes and shapes means that the overall structure will heat up, and therefore expand, unevenly. And of course, many of these new forces are being delivered to these structural components in a non-desirable way.

 

[T.A.M.]

Seems to me like the only thing you need to do to see if there is any credance to the "faster than Freefall" for CDs, is take a bunch of them (if available of video) and time their collapse. If none of them are faster than free fall, than you kind of have your answer. Not a theoretical absolute, but a good practical case study.

TAM

 

[Cl1mh4224rd]

Beyond conjecture, nobody has given figures on either side as to whether thermite or other explosions used in building demolitions. . .

Thermite isn't used in building demolitions. Ever. It's not even an explosive, so it can't create a "low pressure environment".

You're obviously trying to repeat nonsense you've heard somewhere else, but don't even have the remotest clue about what you're talking about. Do you even realize this?

 

[Newtons Bit]

I was correct about the safety factors, from
For you to refute this model, you have to show that the thermal expansion associated with a fire at X degrees was sufficient to cause deflection to the point where the steels yield strength decreased below the value of live and dead loads.

Thermal expansion isn't really an issue. In columns, differential thermal expansion, one side of the building being heated and another not, would have put additional stress on restrained columns. Here's a way to think of this, if you heat up one floor of columns at exactly the same temperature, the entire building will literally grow. If you only heat up one side, the buildings moment frames - which redistributed the forces when some columns were lost - will now restrain those columns (to a degree) and will actually add stress to those columns. This is just heat causing metal to expand.

At 800F, 400C, steel expierences a 0.7 decrease in it's buckling strength. This is due to a loss of stiffness (modulus of elasticity) before the yield stress is even effected. The wide-flanges in this building would see a loss of strength of 0.7, which is equivelent to increasing the load by 143%. 12" A36 box columns are just outside the range of euler buckling at room temperature. They will be affected when the temperature raises. Higher yield stress box columns are likely already affected. I go into this on my (second) blog post @ newtonsbit.blogspot.com if you want to see a little bit more of how it works.

 

[Gravy]

So three things need to be investigated to refute the statements of the CTs:

No. If I claimed that winged unicorns ran the Postal Service, would you be required to investigate and refute my claim? Since the CTs have not supported their "faster than freefall" argument with any evidence or calculations, there's nothing to refute.

I am assuming that the load bearing capability was not compromised after the plane impacts because the building was still standing, and noting that the building was very redundant. Its an assumption but you are assuming the opposite--what grounds are you basing your assumption on?

The Black Knight below also has redundancy and remains standing. Has his load-bearing capability been compromised?

​

 

[beachnut]

I am assuming that the load bearing capability was not compromised after the plane impacts because the building was still standing, and noting that the building was very redundant. Its an assumption but you are assuming the opposite--what grounds are you basing your assumption on?

Bad assumption!

You can not say that an impact energy of 1300 and 2200 pounds of TNT did not compromise the load bearing capacity of the WTC towers. Gee, 2200 pounds of TNT energy is enough to cut all the steel columns in the WTC. When will truthers tell the truth and try to use some facts? When will truthers find some engineers who can explain why the WTC towers failed?

All you need is knowledge to break out and start thinking for yourself. Truthers must stop trusting the truth movement and find some facts. What a bunch of blind followers, the 9/11 truth movement.

 

[Architect]

With the deepest respect, you do not appear to have grasped the points made in my post and I think you don't really follow the issues here. Can I suggest that you re-read it and tell me exactly where you disagree with my explanation, instead of simply repeating your lay interpretation of a limited part of the NIST report?

Turning to the last point, I'm afraid you'll have to be clearer. Are you suggesting that the floor trusses would not fail under floor loadings? Or are you referring to the column work?

Of course, that should be "fire loadings" at the end. [sigh]

 

[Brainache]

covertoperations.blogspot.com/2005/09/great-must-read-but-loooooong-and-very.html


Seems pretty solid to me, can anyone provide some reasons as to whats wrong with it?

Doesn't seem right that covert ops would have a blog. Aren't those guys supposed to be secret?

 

[MG1962]

The Black Knight below also has redundancy and remains standing. Has his load-bearing capability been compromised?

​

Yes because he had to hop around to keep his load transfer intergity intact. And beside Arthur ran away

 

[Loss Leader]

Thermite isn't used in building demolitions. Ever. It's not even an explosive, so it can't create a "low pressure environment".

You're obviously trying to repeat nonsense you've heard somewhere else, but don't even have the remotest clue about what you're talking about. Do you even realize this?

Um, you quoted me as saying, "Beyond conjecture, nobody has given figures on either side as to whether thermite or other explosions used in building demolitions. . . " But I didn't say it. The reason I know I didn't say it is because it's moronic and I am actually fairly bright. Imstellar28 said it.

 

[Cl1mh4224rd]

Um, you quoted me as saying, "Beyond conjecture, nobody has given figures on either side as to whether thermite or other explosions used in building demolitions. . . " But I didn't say it. The reason I know I didn't say it is because it's moronic and I am actually fairly bright. Imstellar28 said it.

Whhoooaaa... I knew I was responding to imstellar28, but I honestly have no clue how I managed to attribute the quote to you. Apologies.

 

[gumboot]

1. Do any explosives used in demolitions create a low pressure environment?

Explosives work by creating over-pressure. Indeed, that's the very definition of "explosion".

2. Is the pressure difference between the falling floor and air above the structure enough to contribute significant forces on the downward movement of the floors?

It would have to be between the falling floor and the ground. If the low pressure differential was ABOVE the floor, it would slow the collapse.

3. Are there any other potential mechanisms which could contribute significant forces to the downward movement of the floors?

Yes. Gravity and an enormous volume of mass falling on them.

-Gumboot