Current Events > Working on my PhD in structures and read the NIST 9/11 investigation report. AMA

(+) Yeah! (+)

More specifically, I am working on my PhD in structural engineering, and I read the NIST NCSTAR1 report which details the investigation and conclusions of the twin tower collapse investigations when taking a class on fire structural engineering in Spring 2018 (so it's been a few years). For those of you with a basic background in mechanics and thermodynamics, the full report is available here:

https://www.nist.gov/publications/federal-building-and-fire-safety-investigation-world-trade-center-disaster-final-report

I believe it is very readable for anybody with a technical/engineering background, and it is legitimately a fascinating report, particularly when if you are familiar with ridiculous conspiracy theories. Of particular interest are chapters 5-8, which are the bulk of the technical details.

AMA, but I'm most interested in questions about structural engineering, fire structural engineering, and the twin towers collapses. Like I mentioned earlier, it's been a couple years so I won't remember all the details, but I remember the gist.

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TC thinks covid is just the flu LMAO
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No_U_L7 posted...

TC thinks covid is just the flu LMAO

I've already admitted those are tasteless jokes in that very topic. Once again, my bad.

Thread in question: https://gamefaqs.gamespot.com/boards/400-current-events/78804773

I deleted those posts at the request of a poster in that topic, but they're all quoted anyway.

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Are robustness requirements, or something similar to prevent progressive collapse, a thing in American building codes? The European standards got some new requirements after 9/11, specifically to make terror attacks less effective.

Whats your phd about? By the sound of it, it has to do with fire or ALS?

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So tell me, can jet fuel actually melt steel beams?

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PatrickMahomes posted...

So tell me, can jet fuel actually melt steel beams?

Was expecting this as post 2

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Jet fuel can't melt steel beams bruh.

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ReeNoiP posted...

Are robustness requirements, or something similar to prevent progressive collapse, a thing in American building codes?

In terms of the general building code, no, not really. There are documents which provide guidelines for how to conduct a progressive collapse type analysis (removal of columns is often a big simulation), but typically those are not required unless the client asks for it. Typical clients which want protections against explosions and terror attacks: oil/chemical plants for accidental explosions, data centers against sabotage attacks (and these are often under strict NDA agreements), government facilities, etc.

The major updates to the US codes have more to do with protecting exits from the building. For instance, sky scrapers are now required to have continuous stairwells to the bottom (the Twin Towers did not have this), structural protection surrounding the stair well (typically concrete walls - the Twin Towers only had sheetrock), and the stairwells must now be separated (on certain floors they were next to each other, which is part of why the planes basically took out all the stairwells upon impact).

I can tell you, however, that Freedom Tower has an extremely robust system thanks to its concrete core: https://www.youtube.com/watch?v=cdWlozmxAJQ

A big reason why progressive collapse wasn't really addressed is that the building would most likely have stood if A) the insulation on the structural members remained intact and B) if there wasn't jet fuel burning inside the building. Note that the fire building code is probably the most backwards code in the US, with fire ratings tests dating back to the 1800s. It is probably the code which is most resistant to engineering evidence based change.

Edit: I'll add that updates to fire codes tend to be a very political issue, and often what really drives the code are reactions to various fire related disasters. The stairwell changes are exactly that. Generally speaking the structural engineer has no input aside from insulation specs, and even then does no analysis to justify it.

ReeNoiP posted...

The European standards got some new requirements after 9/11, specifically to make terror attacks less effective.

In general, Europeans standards regarding fire and collapse are more advanced than US codes. Particularly when it comes to fire structural engineering.

ReeNoiP posted...

Whats your phd about? By the sound of it, it has to do with fire or ALS?

My PhD is actually on simulating earthquakes. More specifically evaluating the system safety of a relatively novel structural system.

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PatrickMahomes posted...

So tell me, can jet fuel actually melt steel beams?

No.

However, at around 500 degrees C steel loses around half of its strength and stiffness, both of which are very important for structural stability. Trust me when I say that's more than enough strength loss to collapse an individual member. Jet fuel can burn around 1000 degrees, and the smoke going upwards can heat the structure to very high temperature.

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Interresting. I never really delved into exactly what happened. I just have to deal with the new requirements now and again. At least its good that we have learned from it and improved building safety.

We dont really have earthquakes here, so I dont know a lot about those. Our main loads are usually live, wind or accidents.

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ReeNoiP posted...

Interresting. I never really delved into exactly what happened. I just have to deal with the new requirements now and again. At least its good that we have learned from it and improved building safety.

We dont really have earthquakes here, so I dont know a lot about those. Our main loads are usually live, wind or accidents.

Work in structural engineering?

At a conference the guy who heads the ASCE7 seismic code committee suggested they're working to simplify and shorten the US wind codes, thank the lord.

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Are you signing the petition with the other thousands and thousands of architects that stated the NIST papers are bullshit, and that there is more to the collapses than what the papers state?

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Does your PhD make your more qualified than Alex Jones on answering questions about the NIST 9/11 report???

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Jabodie posted...

Work in structural engineering?

At a conference the guy who heads the ASCE7 seismic code committee suggested they're working to simplify and shorten the US wind codes, thank the lord.

Yes, I have been a structural engineer for almost 10 years by now. I mostly work with heavy lifts and temporary steel structures during the construction phase.
Its pretty cool. I get to be part of some big projects, and be there to see the things I have designed in action.

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It seems like an awesome thing to study but I have no way to discern how much of it is true.

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N3xtG3nGam3r posted...

Are you signing the petition with the other thousands and thousands of architects that stated the NIST papers are bullshit, and that there is more to the collapses than what the papers state?

No. The Twin Tower collapses are likely the most thoroughly investigated and well understood major collapses in the US. Architects are typically not educated in building mechanics, particularly not in very niche and highly sophisticated fields like fire structural engineering. There are like 3 structural engineering programs that even have a fire based class at the grad level in the US, and the only practicing fire structural engineers are PhD hires which assist in signature (expensive and architecturally demanding) projects. Keep in mind the current US building codes lack even a rudimentary consideration for thermodynamics, and fire ratings tests we used today were designed in the 1800s and have been proven to be mostly useless by engineering research in terms of actually predicting the performance of a structural member in fire design. But the sequence of events leading to collapse was 95% corroborated with evidence coming from time stamped pictures and videos, with the exceptions primarily being fires in areas that weren't predicted numerically.

The majority of structural engineers have likely not even seen material properties for building materials at high temperatures, and many do not even have to take basic thermodynamics courses in their education (I did, but I did not have to). And much of their evidence has to do with them not believing the collapses "look" right, which imo does not hold much water considering just how the loading, structural system, and collapse mechanisms were.

To put it in another light: in order to determine the necessary load capacity we conduct highly detailed analysis, and then size members according to equations that have been proven through good engineering research to reflect the true strength of a member with a reasonable margin of safety. This requires many hours of detailed analysis, strict specifications in regards to placement, material properties, construction error tolerance, load patterning, and a variety of load scenarios based on in depth statistics based risk analysis. Fire insulation, on the other hand, is picked from a table based on your member size based on dated and useless test. Keep in mind we could easily be conducting rudimentary thermodynamic analyses and appropriately design our fire protection around it. And that even ignores more in depth analysis which can consider material softening and weakening effects, and structural phenomena such as catenary and tensile membrane action.

There is a lot more uncertainty to 7 WTC's collapse because that analysis was much more dependent on variables which cannot be verified post collapse, and there is good reason to doubt the validity of those results. However, that does not suddenly make it more likely they were destroyed by controlled demolition.

In short, no. There is a mountain of physical and numerical evidence supporting the prevailing theories, and further research into steel under extreme heat conditions has, by and large, corroborated the NIST findings rather than contradict any of their conclusions.

Edit: Or in another way: the collapses themselves essentially spawned/inspired an entire new field of study within structural engineering. 20 years may not seem old to you, but the vast majority of structural engineers going to school in the US today get no exposure to it, which is up by when zero structural engineers got any exposure to this field prior to the collapses. The NIST collapse studies were breakthrough interdisciplinary studies, and are frankly huge engineering achievements in that regard.

Shadow Don posted...

Does your PhD make your more qualified than Alex Jones on answering questions about the NIST 9/11 report???

If I'm honest with you, no, not really. The real qualification is having studied a basic fire structural engineering course by one of the top US researchers in the field. The vast majority of structural engineers, even at the PhD level, will have little to no exposure to how buildings interact with fires from an engineering/thermodynamic perspective. There are plenty of idiot PhDs as well.

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boredom bump

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I just got the 9/11 Report and Post 9/11 graphic novels.

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billcom6 posted...

I just got the 9/11 Report and Post 9/11 graphic novels.

This?

https://www.amazon.com/11-Report-Graphic-Adaptation/dp/0809057395

Pretty interesting, I've never heard of it before.

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Jabodie posted...

This?

https://www.amazon.com/11-Report-Graphic-Adaptation/dp/0809057395

Pretty interesting, I've never heard of it before.

Yeah, and this
https://www.amazon.com/After-11-Americas-Terror-2001/dp/0809023571/

The library at my school was getting rid of books so I got them for free.

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billcom6 posted...

Yeah, and this
https://www.amazon.com/After-11-Americas-Terror-2001/dp/0809023571/

The library at my school was getting rid of books so I got them for free.

If I'm honest I don't really know anything about international politics lol. I really only know stuff about buildings. Maybe it'll be something interesting and digestible to read though.

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Structural engineers seriously don't normally go through a thermodynamics class? That seems...weird, to me

I'm taking the class this fall semester, and I'm really looking forward to it
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@Jabodie
Good post. Im glad you acknowledge the disconnect in evidence for T7. I think tower 7if there is any conspiracywould likely be where there is fuckery going on. A lot of things about its collapse, and what was housed within it, seem very suspect. The petition I was referring to actually has 7 as its main focus.

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