NIST's Creep Effect Theory - A study in the works

As those of you who are active in the 9/11 discussions may know, I have scoffed at the NIST's claim that creep effects played a significant role in the failure of the structural elements of WTC 1 and WTC 2. In numerous posts here I have pointed out that creep, an effect of permanent deformation of a metal due to the combination of high loading and high temperatures, is a long-term effect. Long-term being of the order of tens of thousands of service hours under these conditions. NIST claims that in a matter of 45 minutes to 1 hour the elevated temperatures along with the increased loading on structural columns due to the loss of other columns resulted in creep significant enough to facilitate column failure.

As I have also pointed out in past posts, creep does not come into play until temperatures exceed approximately 650 F. NIST's own report caps the elevated temperatures of structural columns at about 600-650 F. And then goes on to state that no structural elements were exposed to these elevated temperatures for the duration of the time between impact and collapse. Creep necessarily requires a maintained elevated temperature.

I have just had to decommission a High Pressure/High Temperature curing chamber. This chamber has an operating envelope of up to 800 F and 10,000 psi. The chamber has been permanently put out of service not because of creep, but due to corrosion and electrolysis that occurs when dissimilar metals are put in an environment of combined electrical current and water (electrical current being the heating elements that were used to heat the chamber). The corrosion had finally caused galling of the threads that required the chamber lid be destroyed in order to get opened.

According to the NIST creep theory this chamber would have had to have been decommissioned due to permanent deformation that would have caused the metal to metal seal and/or the threads to deform to the point the lid could not seal - and this deformation, according to NIST's claims - would have happened within the first 24 hours of the chamber being subjected to it's maximum operating conditions.

Not only did this not occur within in the first 24 hours of operation, but did not occur after 35 years of service the chamber has seen. I am currently writing a proposal to my management requesting we preserve the chamber for destructive metallurgical testing so that we can learn things that will help us design better HTHP pressure chambers in the future. I will ask permission to share those findings and if allowed will come back to you with them. This study will probably not take place until next fiscal year.

Hope all is well with you all.

Kindest Regards,
Val.

Hey FishermanFred...err I mean Valhall. Nice to see you back. Hope all is well with you.

You may be compairing apples and oranges here. Your curing chamber was designed to handle the temperatures and pressures that it operated at. These temperatures and pressures were the normal environment for this chamber not an extreme. The alloy of steel used in its construction was selected for it's ability to maintain enough strength for the operation of this chamber plus a factor of safety. You stated that the chamber was not removed from service because of a failure from temperature or pressure, but due to the effects of corrosion. The structures of the WTC were exposed to extremes in both the force of impact from the aircraft and then from the temperatures from the fires. I can't see how the two can be compaired.

Originally posted by JIMC5499
The alloy of steel used in its construction was selected for it's ability to maintain enough strength for the operation of this chamber plus a factor of safety.

Factor of safety aside (were those chamber walls thicker than the box columns in core, Val?),

This was taken from page 54 (61 of the PDF) of the University of Edinburgh study on the effects of heating on steel-framed structures:

The temperature dependent stress-strain properties of concrete and steel were taken from EC2 [3] and EC3 [2] respectively. As discussed earlier the effect of steel stress-strain properties is very limited and the results are not sensitive to minor variations in these.

www.studyof911.com...


Claiming foul on the type of steel, unless drastically different and therefore not even steel by conventional standards, is doing what's called "playing the subtleties" as if they make huge differences, when they do not. The above quote is from an extensive study involving lab tests. All you have are words you can post on a forum, JIMC.

"Playing the subtleties" as, in other words, comparing two different colored apples and saying one is an orange.

[edit on 21-6-2007 by bsbray11]

Jim,

Let me explain why we've got apple pie on both plates.

Creep, BY DEFINITION, is the PLASTIC deformation of a material while it is loaded in the ELASTIC stress/strain region. So that "WTC Steel" is 50,000 psi and "Chamber Steel" is 60,000 psi makes no difference to the affect of creep. Creep is a thermally induced permanent "set" of what should be a reversible and purely elastic strain. In other words, I could put 10,000 psi of stress into a 50,000 psi yield strength material and still PLASTICALLY deform it IF the load is done under a high enough temperature and for a long enough time.

Hope that helps to show that this is, in fact, a very applicable comparison for the WTC steel "creep" theory.

*hi Griff*