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

[000063]

It's the NIST theory, not mine. I just showed that it is impossible.

Except for the parts you agree with, right?

 

[Seymour Butz]

He's ignored all of this before.


,,, and I am an electronics tech.

Personally, I'm just curious if he'd settle for a "win", even if it disproves cd.

Cuz I believe that someone else in this thread mentioned that CTBUH is suggesting as thermal contraction as a more possible cause.

 

[jaydeehess]

The CTBUH said that they would have preferred NIST to have included the cooling phase but specifically state their support of fire induced collapse

 

[tfk]

Gamolon,

CSA of W24 x 55 beam=15.986 sq. inches, the modulus of elasticity of steel is 29 million lbs./sq. inch, length is 52 feet x 12 inches/foot = 624 inches

force generated by beam for a 5 inch expansion is force = [5 inches x 15.986 sq. inches x 29,000,000 lbs./sq. inch] / 624 inches = 3,714,753 lbs, and for five beams would be 18,573,768 lbs buckling force = [Pi^2 x modulus of elasticity of steel x area moment of inertia] / [(effective length factor x unsupported length of beam)^2] = [9.8696 x 29,000,000 lbs/sq. inch x 29.1 in^4]/[(2 x 624 inches)^2] = 5,347 lbs, so the max force of the 5 beams is 26,738 lbs.30 x 3/4" diameter shear studs on the girder, so their total cross sectional area was Pi x R^2 x 30 = 13.25 sq. inches. The shear stress is just force/unit area and is thus 26,738 lbs. / 13.25 sq. inches = 2,018 psi
The shear studs would have had a tensile yield of 36,000 psi and a shear yield of 57.7% of that at 20,772 psi. The shear stress would only be 10% of what the shear studs could take.

tfk (or anyone else),
When you have a moment, can you explain to me this calculation provided by gerrycan? He used this to show that the shear studs on the floor beams should have restrained the beam from thermally expanding.

Is this correct? I see NIST did calculations in their report that show that the shear studs would have failed. I asked gerrycan to address this as he said that NIST OMITTED the shear studs in their calculations, but he has not yet addressed this. What is the difference between the two calculations and where did gerrycan's engineer friend go wrong (if he/she did get it wrong).

Thanks in advance.

There is virtually nothing about this calculation that is correct.

Here are his mistakes:

His biggest mistake is the most obvious one: there were no shear studs connecting the girder to the concrete floor. NIST was very explicit about that.

But if he were trying to figure out if the girder shear studs would have failed IF they were really there, then he screwed up a bunch of things.

1. He uses the wrong E value. He uses room temp E, instead of high temp E.

2. IF the girder shear studs would have survived, then the shear studs on the beams would also have survived. So he's got to figure out how much of the expansion load those studs would have supported. He didn't do this.

3. He has laid out the problem as though the lateral stiffness of the girder is essentially infinite. This is false. The lateral stiffness of the girder is significantly less than the axial stiffness of the beams. In this case the girder will flex laterally, and he must consider this in calculating the resultant loads on his (imaginary) studs.

3. As a result of the flex of the girder, the loads from each girder will be concentrated on the (imaginary) studs that are immediately adjacent to each beam connection, and not uniformly shared amongst the (imaginary) studs.

4. He is assuming that the failure mode of his (imaginary) studs is shearing of the studs. This is false. The failure mode is fracturing of the concrete, which happens at a significantly lower stress level than the shearing of the (imaginary) studs.

5. He forgot to include the portions of the loads taken up by the bolts on either end of the girder.

6. 5 digits of precision is absurd.

7. All in all, the right way to do this calculation is with a quick FEA.

Mr. Gerrycan should stay out of mechanical analysis.

 

[tfk]

No, I'm assuming that everything is about the same temp, as would be the case.

Thermal expansion of the girder would put more of it over the support plate.

But all that ignores the point:

Thermal expansion cannot result in 5.5" of axial elongation because sag would shorten the beams more than they expanded before then.

At 600^oC the beams would expand 4.68" and lose 0.27" to sagging for a net elongation of 4.41"

At700^oC the beams would expand 5.63" and lose 3.495" to sagging for a net elongation of 2.135".

The NIST theory of the beams pushing the girder off its seat is not possible.

And your numbers are supplied by two people (gerrycan & you) who don't know what they are talking about.

 

[Seymour Butz]

The CTBUH said that they would have preferred NIST to have included the cooling phase but specifically state their support of fire induced collapse

Thanks!

I'm guessing though that CTBUH could be supporting a fire induced collapse, with the thermal contraction phase being the most likely cause?

I'm no longer familiar with what they said, so feel free to correct me.

 

[jaydeehess]

Thanks!

I'm guessing though that CTBUH could be supporting a fire induced collapse, with the thermal contraction phase being the most likely cause?

I'm no longer familiar with what they said, so feel free to correct me.

They are definately supporting a fire induced collapse. I do not believe they came out and stated a more probable scenario, only that they believe that NIST would have been better served in their study by also having analyized contraction possibilities.

I have cajoled Chris 7 many times to just do it, go ahead and write up a paper illustrating why he comes to a conclusion that differs from NIST. It could be published in many different magazines and journals. The only caveat would be that in order to get published the very first thing he would have to do is drop the "NIST lied", and " NIST's reports are fraudulent".

It is that very issue that I believe is one, if not the main reason, why C7 does not do this, and why he steadfastly refuses to even respond to posts suggesting it. Its the same reason why PfT won't do it with their opinion that the DFDR illustrates a different flight path for AA77 than does the physical damage on the ground. They just cannot psychologically and emotionally separate themselves from these purely technical matters.

There are of course other reasons, among them I suspect are, fear that they will be shown to be wrong, and a paranoia that TPTB will excoriate them publically, perhaps even worse, if they do anything other than prowl the internet forums. Perhaps they believe that they must first garner a very large essentially underground, following via social media, that just as the Arab Spring was orchestrated by such, they too can bring their message to the forefront.

Who knows, they don't talk about it.

 

[sheeplesnshills]

OK, some nice math you got there to get to that conclusion. Why not tell me where the video is wrong and I could address it. And again, my qualifications are none of your business.

One obvious problem with your account is that you assume the beam has to be pushed all the way off the plate for it to fail......I doubt that's the case as the support plate itself may well fail when the one end of it is overloaded. Next you have to show that the large lower plate is positioned so that if the support fails and the beam starts to roll off that it would stop that roll....seems doubtful. And of course you need to show that welds on the two side plates would be strong enough not to simply fail in shear due to the expansion loads.
Come back with the math on those points and then we can talk.......

 

[LSSBB]

One obvious problem with your account is that you assume the beam has to be pushed all the way off the plate for it to fail......I doubt that's the case as the support plate itself may well fail when the one end of it is overloaded. Next you have to show that the large lower plate is positioned so that if the support fails and the beam starts to roll off that it would stop that roll....seems doubtful. And of course you need to show that welds on the two side plates would be strong enough not to simply fail in shear due to the expansion loads.
Come back with the math on those points and then we can talk.......

Also, a complete tolerance stackup from ground to the plate and including the outer walls could put a large enough window on the connection to make it a high probability for the beam to come off the plate even if the raw calculations don't take it there. And they cannot get an approximation of that probability without FEA and Monte Carlo.

 

[ozeco41]

Is everyone still assuming that the two columns will remain in their exact location?

That distances between columns measured to the inch or fraction of inch are valid in a building subject to fires?

Where the fires could quite possibly warm up the columns and other beams attached to them? (yeah - so we don't miss it [/sarcasm] )

How can we seriously consider distances to the inch in this setting???


[/lone voice in wilderness

 

[BasqueArch]

When faced with facts you can't dispute you and Noah and many others here resort to denial and childish insults.

The only facts you have are that NIST said the girder was pushed at least 5.5" and that one of the drawings says the plate was 1'0" wide. Everything else you are making up.

Facts that you neglect (because you lack the education of a structural or mechanical engineer) are that steel will fail at a sufficient temperature/stress combination. And as tfk noted once the bolts sheared , the girder was unstable to the horizontal, vertical, moment forces active on it.

The girder carried a large weight from a large contributing floor area, supported at two points. The web stiffeners were there to resist web shear. They did nothing to resist the horizontal forces that pushed (or pulled) the girder off the wimpy 1" seat, or reinforced the hot seat that could have failed beneath it. This is an uneducated red herring by those without the education to know better.

Other facts are there is no evidence that high explosives were used, or therm*te. There are no means other than damage by fire that can explain the global failure of WTC7.

 

[triforcharity]

Is everyone still assuming that the two columns will remain in their exact location?

That distances between columns measured to the inch or fraction of inch are valid in a building subject to fires?

Where the fires could quite possibly warm up the columns and other beams attached to them? (yeah - so we don't miss it [/sarcasm] )

How can we seriously consider distances to the inch in this setting???


[/lone voice in wilderness [qimg]http://conleys.com.au/smilies/scratch.gif[/qimg]

Excellent point sir! And that right there is why you're an engineer, and I am not.

Forgive my ignorance, but is that creep?

 

[ozeco41]

Excellent point sir! And that right there is why you're an engineer, and I am not.

Could be. It is also related to the fact that I won't engage C7's trolling. HOWEVER I pointed out the centrepiece of his trickery at this post back on 17 March and have reminded folks of that bit of wisdom several times since. The original bit of trickery was to pretend that this was a single factor problem - linear expansion or contraction. And members were prepared to go along with C7's false constraints. C7 has since admitted sag into his version and tfk has pointed out several more factors.

...Forgive my ignorance, but is that creep?

Maybe, probably not. It's not so simple. The columns almost certainly moved from original location. Several factors could cause that in the same way that several factors contribute to the girder walk off. Creep could be one of the factors. I haven't a clue how big a factor.



BTW "I haven't a clue" is engineer's terminology often used in this sort of situation. Usually associated with a shrugging action of the shoulders.

 

[triforcharity]

Could be. It is also related to the fact that I won't engage C7's trolling. HOWEVER I pointed out the centrepiece of his trickery at this post back on 17 March and have reminded folks of that bit of wisdom several times since. The original bit of trickery was to pretend that this was a single factor problem - linear expansion or contraction. And members were prepared to go along with C7's false constraints. C7 has since admitted sag into his version and tfk has pointed out several more factors.

I always knew C7 was talking out of his rear, and over his head for quite some time now. This pretty much confirms it.

Maybe, probably not. It's not so simple. The columns almost certainly moved from original location. Several factors could cause that in the same way that several factors contribute to the girder walk off. Creep could be one of the factors. I haven't a clue how big a factor.

Gotcha. Which makes perfect sense. It's not like fire is ONLY going to have an affect on one piece of the assembly around column 79. It's going to have an affect of the whole damn thing. Some parts more than others. Especially the thinner parts, which are of course more vulnerable to heat.

BTW "I haven't a clue" is engineer's terminology often used in this sort of situation. Usually associated with a shrugging action of the shoulders.

I do the same thing, often. Especially with an inexact and often confusing phenomena like fire.

Cheers Oz!

 

[Animal]

Excellent point sir! And that right there is why you're an engineer, and I am not.

Forgive my ignorance, but is that creep?

I typically don't like wikipedia....but this is a simple explanation......

"In materials science, creep is the tendency of a solid material to move slowly or deform permanently under the influence of stresses. It occurs as a result of long term exposure to high levels of stress that are below the yield strength of the material. Creep is more severe in materials that are subjected to heat for long periods, and near melting point. Creep always increases with temperature.

The rate of this deformation is a function of the material properties, exposure time, exposure temperature and the applied structural load. Depending on the magnitude of the applied stress and its duration, the deformation may become so large that a component can no longer perform its function..........Unlike brittle fracture, creep deformation does not occur suddenly upon the application of stress. Instead, strain accumulates as a result of long-term stress. Creep is a "time-dependent" deformation.........As a rule of thumb, the effects of creep deformation generally become noticeable at approximately 30% of the melting point"

 

[Animal]

Could be. It is also related to the fact that I won't engage C7's trolling. HOWEVER I pointed out the centrepiece of his trickery at this post back on 17 March and have reminded folks of that bit of wisdom several times since. The original bit of trickery was to pretend that this was a single factor problem - linear expansion or contraction. And members were prepared to go along with C7's false constraints. C7 has since admitted sag into his version and tfk has pointed out several more factors.


Maybe, probably not. It's not so simple. The columns almost certainly moved from original location. Several factors could cause that in the same way that several factors contribute to the girder walk off. Creep could be one of the factors. I haven't a clue how big a factor.



BTW "I haven't a clue" is engineer's terminology often used in this sort of situation. Usually associated with a shrugging action of the shoulders.

His whole sag claim is false since there no way to determine what building elements remained that would have resisted sagging and how much. It is just more making stuff stuff up that troofers are famous for.

 

[tfk]

gerrycan,

You came here saying that you wanted to discuss the issues associated with the walk off of the girder.

Yet, when I've asked you some questions about your calculations, you go silent.

Is there some particular reason for this?

I asked you some specific questions in this post and this post.

Would you care to answer those question?


tom

 

[ozeco41]

His whole sag claim is false since there no way to determine what building elements remained that would have resisted sagging and how much. It is just more making stuff stuff up that troofers are famous for.

True. We are coming at the same issue but using different words.

Bottom line is - there are lots of factors involved and he is only acknowledging two of the four that are probably the most important.

 

[Animal]

True. We are coming at the same issue but using different words.

Bottom line is - there are lots of factors involved and he is only acknowledging two of the four that are probably the most important.

He is just cherry picking to factors, then trying to disprove them by ignoring all the other contributing factors. Just more dishonesty by troofers

 

[tfk]

I typically don't like wikipedia....but this is a simple explanation......

"In materials science, creep is the tendency of a solid material to move slowly or deform permanently under the influence of stresses. It occurs as a result of long term exposure to high levels of stress that are below the yield strength of the material. Creep is more severe in materials that are subjected to heat for long periods, and near melting point. Creep always increases with temperature.

The rate of this deformation is a function of the material properties, exposure time, exposure temperature and the applied structural load. Depending on the magnitude of the applied stress and its duration, the deformation may become so large that a component can no longer perform its function..........Unlike brittle fracture, creep deformation does not occur suddenly upon the application of stress. Instead, strain accumulates as a result of long-term stress. Creep is a "time-dependent" deformation.........As a rule of thumb, the effects of creep deformation generally become noticeable at approximately 30% of the melting point"

Animal,

Creep is not just temp & time dependent, but also extremely stress level dependent.
___

From Journal of Engineering Mechanics ASCE , Vol. 134 (2008)
What Did and Did not Cause Collapse of WTC Twin Towers in New York
Zdenek P. Bazant, Jia-Liang Le, Frank R. Greening and David B. Benson

Page 2:

"But are high steel temperatures really necessary to explain collapse?

Not really. The initial speculation that very high temperatures were necessary to explain collapse must be now revised since tests revealed a strong temperature effect on the yield strength of the steel used. The tests by NIST (2005, part NCSTAR 1-3D, p. 135, Fig. 6-6) showed that, at temperatures 150° C, 250° C and 350° C, the yield strength of the steel used in the fire stories decreased by 12%, 19% and 25%, respectively. These reductions apply to normal durations of laboratory strength tests (up to several minutes). Since the thermally activated decrease of yield stress is a time-dependent process, the yield strength decrease must have been even greater for the heating durations in the towers, which were of the order of one hour. These effects of heating are further documented by the recent fire tests of Zeng et al.(2003), which showed that structural steel columns under a sustained load of 50% to 70% of their cold strength collapse when heated to 250° C.

Although a detailed computer analysis of columns stresses after aircraft impact is certainly possible, it would be quite tedious and demanding, and has not been carried out by NIST. Nevertheless, it can easily be explained that the stress in some surviving columns most likely exceeded 88% of their cold strength S0 . In that case, any steel temperature ≥150° C sufficed to trigger the viscoplastic buckling of columns (Bazant and Le 2008). This conclusion is further supported by simple calculations showing that if, for instance, the column load is raised at temperature 250° C from 0.3Pt to 0.9Pt (where Pt = failure load = tangent modulus load), the critical time of creep buckling (Bazant and Cedolin 2003, chapters 8 and 9) gets shortened from 2400 hours to 1 hour (note that, in structural mechanics, the term ‘creep buckling’ or ‘viscoplastic buckling’ represents any time-dependent buckling; on the other hand, in materials science, the term ‘creep’ is reserved for the time-dependent deformation at stresses < 0.5S0 , while the time-dependent deformation at stresses near S0 is called the ‘flow’; Frost and Ashby 1982).

Therefore, to decide whether the gravity-driven progressive collapse is the correct explanation, the temperature level alone is irrelevant (Bazant and Le 2008). It is meaningless and a waste of time to argue about it without calculating the stresses in columns. For low stress, high temperature is necessary to cause collapse, but for high enough stress, even a modestly elevated temperature will cause it."

This effect (accelerated creep due to high stress levels) was crucial in the towers because of the stress redistribution due to physical damage.

Less important in WTC7, because the stress levels didn't increase all that much over their design levels.


tom