Kai Kostack's WTC7 Collapse Simulation using BCB and Blender

[Mick West]

Source: https://www.youtube.com/watch?v=VAkTbyENZ5s

Kostack Studio
Published on Sep 11, 2017

Simulated with completely new developed software designed for structural simulation, this revision of my earlier WTC7 simulation attempt serves as validation case for the software.

New in this simulation compared to the old one:
- Multiple constraints per connection are used to represent individual degrees of freedom (DOF)
- Breaking thresholds are computed from real world parameters
- Correct steel thicknesses and beam dimensions are used
- Plastic deformation is now simulated

While this simulation of World Trade Center 7 is still not 'perfect' it resembles much better the specific characteristics observed in reality than the older model. This simulation confirms mostly the findings of NIST, it is safe to say that the columns 79 to 81 were the first columns which gave way because the removal of other columns led to much different collapses. More than that is hardly determinable, such a system behaves just to chaotic to tell what exact connection failed first. In this regard NIST might be wrong by declaring a specific failure point. However, I consider this not being an important question given the fact how compromised the structure around these three columns must have been exposed to fire for hours, a situation beyond any imaginable safety design specification.

Having said that, I want to emphasize that this video is not intended to prove or disprove 9/11 conspiracy theories. I'm deleting comments that include hate speech, so you better think twice before starting an argument about the reasons of 9/11 here. Instead, I recommend to read a neutral source like: https://en.wikipedia.org/wiki/9/11_co... to get some pros and cons instead of watching YouTube videos.

This is a private project. There are no third parties involved. There is no scientific report available. No peer review has taken place. Thanks for watching.

An impressive project for one individual, Kostock's simulation is an amazing static model of WTC7, and gives a reasonable facsimile of the collapse, given the limitations of what he is doing.

People will surely pounce on the fact that the outer skin does not behave the same as the real event.

But as with the NIST simulation, this demonstrates an interior collapse followed by the exterior bucking and falling.

Overall a very impressive effort.

It also provides some new viewpoints, that might be helpful perspective.

 

[Jeffrey Orling]

What he seems to ignore are the impact of the transfers in the form of the collapse. He presents the model as if there were NO transfers. Whether the collapse of the region around col 70 was at floor 13 or 12 or whatever floor... the descending floor masses and steel surely dislodged/destroyed the load transfer structures... which would show a different collapse FORM and SEQUENCE. Once the transfers failed... and their failure likely was east to west... the entire inside would collapse INCLUDING undermining the facade... which likely lagged just a bit behind the collapse of the interior.

 

[Nada Truther]

He showed the 3d scan of the debris pile, but I wonder how an actual photo of the pile vs. his pile would compare. How would the skin sections compare? I found some, but don't have the know-how to super-impose and all of that for comparison.

Also, besides what Jeffrey posted in post #2, how open for "tweaking" is this simulation to sway it toward what we "want" to see? How easy will it be for some to argue that you could make the collapse look like whatever you want it to look like to reflect your own personal opinion?

 

[Oystein]

As long as the tweaking is within a plausible envelope of the unknown variables, it is fine. If such tweaking shows that lots of forms and features are possible, including those actually observed, this would to pad the credibility of the "no demolition devices after initiating local failure" class of theories.

Invalid tweaks would include adding entities that weren't actually there, like extra elements, unrealistic life loads, or indeed demolition devices.

 

[Mick West]

What he seems to ignore are the impact of the transfers in the form of the collapse.

It's far from a perfect model, and much less exact than NIST's models. But the point here is an illustration of the very broad principles of collapse. Compare it with an attempt I made for WTC1:

Kostack's model is the best independent model available. Unfortunately as it's not exactly the right collapse people will nit-pick. However the intent is, like with mine, to illustrate general principles and characteristics. Here he failed columns 79-81, and the collapse was as shown, similar to the real world in many aspects.

I think the benefit here is that people will look at the actual structure of WTC7, and perhaps understand more about how the "interior then exterior" collapse might work.

 

[Mick West]

Another thing he does is add damage to the model to match the photos. Now this is a little speculative, as we don't have great close-ups of the damage, but there's a reasonable visual match.

 

[Mick West]

His southwest corner damage seems wrong though, as the corner column (15) is intact

Whereas photos and the NIST analysis suggest otherwise.

(Figure 12-33)

 

[Jeffrey Orling]

My point is that the collapse sequence likely involved the collapse of the transfers EARLY on... THEN the structure above in the center and west came down.

sequence would be something like this:

failure at column line 79 and 80 (this could occur anywhere from floor 5 - 13 or higher even. But for the falling mass to collapse transfer trusses below it would likely have to be multiple floor masses from above as those trusses supported 40 stories and were massive.

collapse of transfer truss 1 and 2 (don't know which came first) This led to the kink in the north face and then collapse of the EPH thru the building

collapse of the main East-West girder at floors 3-5 at the north side of the core which led to:

collapse of the MG 23 which were supported on main East-West girder on their west side which led to:

collapse of the center of the tower up to:

collapse of transfer truss 3 which led to the collapse of the WPH which led to the collapse of the braced frames of the facade on floors 1-7 which led to the collapse AND counter clockwise rotation and folding inward at column line 47 or 48 of the facade which pivoted about the structure on the west side up to floor 8

The facade fell on and folded over the collapsed materials.

The collapse was driven by FAILURES at the transfer structure level... We don't know what triggered those failures... falling debris from above... or connection (bolt) failures on one of the trusses (bolts being the way the members were connected one to the other.

 

[Mick West]

My point is that the collapse sequence likely involved the collapse of the transfers EARLY on... THEN the structure above in the center and west came down.

Well, perhaps you should encourage someone to simulate that. But this is getting a bit off topic.

 

[Jeffrey Orling]

Well, perhaps you should encourage someone to simulate that. But this is getting a bit off topic.

I hereby officially am encouraging someone to model this!

 

[deirdre]

rereading this thread since someone just linked to Kostacks simulation and i'm struck again at how much I trust "computer guys" to do computer simulations over engineering students (ie Hulseys wtc7 report and data dump)

 

[Abdullah]

The problem is the core column group 2 fails near simultaneously (within a s cond) with group 1.

Then in the next second groups 3 and 4 fail at the middle floors

After a 3 second delay, group 5 fails around the fire floors

And in the next second the remaining building topples east about the very bottom floors

With very inaccurate results

 

[Thomas B]

Another thing he does is add damage to the model to match the photos.

I pointed this out on another thread, but NIST seems to think that the damage from the other collapses played no significant role in the destruction of WTC 7:

In response to comments from the building community, NIST conducted an additional computer analysis. The goal was to see if the loss of WTC 7's Column 79—the structural component identified as the one whose failure on 9/11 started the progressive collapse—would still have led to a complete loss of the building if fire or damage from the falling debris of the nearby WTC 1 tower were not factors. The investigation team concluded that the column's failure under any circumstance would have initiated the same sequence of events.
Content from External Source

https://www.nist.gov/world-trade-center-investigation/study-faqs/wtc-7-investigation

This raises an interesting question. Does Kostack's model collapse (after the failure of column 79) without the damage?

And this raises another question as well: if the failure of column 79 would have caused total collapse "under any circumstances", why did the damage (which apparently included severing columns) not immediately cause the collapse?

Has column 79 been identified as the Achilles' heel of the building? Should a building have such vulnerability?

Does Kostack's model fail completely only with the failture of column 79? Which other columns would have done the trick?

 

[FatPhil]

Does Kostack's model fail completely only with the failture of column 79? Which other columns would have done the trick?

At times like this, it's sometimes good to share what would be your conclusions given the two possible outcomes to the first question before it's proffered. (Admittedly, the "no" answer does invite the follow-up question's answer too.)

 

[Thomas B]

At times like this, it's sometimes good to share what would be your conclusions given the two possible outcomes to the first question before it's proffered. (Admittedly, the "no" answer does invite the follow-up question's answer too.)

Kostack's model, like WTC7, appears to have been able to sustain a substantial amount of damage to the exterior columns without collapsing. And yet, the subsequent failure of a single column in the interior of the building precipitated a total collapse.

According to NIST, the damage to the exterior did not weaken the building in a way that was crucial for its collapse. It would have collapsed even if nothing had happened to the building but the failure of column 79. I'm not sure, but I think this means that it was vulnerable to a localized fire around that column all along. That is, the exterior damage did not make the heat expansion more devastating in the final outcome.

So, if Kostack's model behaves like NIST's model when undamaged, we can use it to explore some of the questions that truthers like to raise: how is it reasonable that a building is designed with this vulnerability? We all agree it shouldn't need to account for events like 9/11. But surely it should anticipate a sustained fire around a single column? Surely, it should be designed so that any one column is redundant "under any circumstances"?

But if Kostack's model fails completely only after the exterior damage and does so regardless of which column you buckle to initiate it, then it isn't really a model of the building (as NIST describes it). It would be much stronger in its initial state than NIST's model, and much weaker after the damage has been done. So that would cast the model into doubt for me.

It would only prove that a model can completely collapse by the removal of a single element. A house of cards already proves that. We need something that is plausibly resilient to collapse in its initial state but also plausibly vulnerable. My questions are testing whether (we know whether) Kostack's model fits this bill.

 

[Abdullah]

how is it reasonable that a building is designed with this vulnerability?

Precisely. The failure to condemn this glaring flaw and make a scandal out of it is one of the biggest drivers of skepticism. It needs to be said: Building 7 was a dusaster waiting to happen.

 

[Mendel]

how is it reasonable that a building is designed with this vulnerability? We all agree it shouldn't need to account for events like 9/11. But surely it should anticipate a sustained fire around a single column? Surely, it should be designed so that any one column is redundant "under any circumstances"?

How reasonable is it to require every building in NYC to survive a fire burning for half a day with the sprinkler system (partially) disabled? Who pays the cost for this requirement? And how many more hours would it have taken for other columns to collapse under these circumstances?

Most structures (e.g. bridges) collapse if you remove (or degrade) a load-bearing element. They're designed so that this does not happen under the worst expected circumstances, which includes standing up to a certain amount of office fire via its sprinkler system and the subsequently arriving fire department. I think that's reasonable.

What is not reasonable is to keep using degraded structures into failure. That's why WTC7 was evacuated, and fire fighters withdrawn: I expect no lives were in danger when it collapsed? because it was designed to enable this evacuation (as were the towers, but the design assumptions about the stairwells did not hold, and the building codes were subsequently changed).

Compare instead this:

Article:

On Friday, January 28, 2022, about 6:40 a.m. eastern standard time, the Fern Hollow bridge, which carried Forbes Avenue over the north side of Frick Park, in Pittsburgh, Allegheny County, Pennsylvania, experienced a structural failure. As a result, the 447-foot-long bridge fell approximately 100 feet into the park below. At the time of the collapse, a 2013 New Flyer articulated bus, operated by the Port Authority of Allegheny County, and four passenger vehicles were on the bridge. A fifth passenger vehicle drove off the east bridge abutment following the collapse and came to rest on its roof on the exposed ground below. As a result, 10 vehicle occupants sustained injuries.

Initial assessment of bridge components indicates that the collapse initiated at the west end of the structure.

Source: https://www.ntsb.gov/investigations/Pages/HWY22MH003.aspx

Article:

The Fern Hollow Bridge was inspected annually, and as recently as September 2021, but it was never ordered to be closed.

Source: https://www.publicsource.org/allegheny-pittsburgh-bridge-rating-infrastructure-collapse/

In my opinion, a bridge that collapses unexpectedly is not "reasonable", but a building that collapses predictedly after several hours of fire is reasonable enough.

 

[Abdullah]

@Mendel that's not the problem. The problem is that the failure of just three columns directly lead to the collapse of the entire eastern lobe.

 

[Mendel]

@Mendel that's not the problem. The problem is that the failure of just three columns directly lead to the collapse of the entire eastern lobe.

WHY is this a "problem"? (and what is the "eastern lobe"?)

 

[Abdullah]

@Mendel because it's really dumb and dangerous and easily fixable. The Towers didn't have this issue.

 

[deirdre]

The failure to condemn this glaring flaw and make a scandal out of it is one of the biggest drivers of skepticism.

no it isn't. I've been on Metabunk for 8 yers and youre the first person i've heard say this.

 

[Abdullah]

@deirdre yes it is. How have you not heard truthers complaining about how according to the official version all skyscrapers are weak and unsafe?

 

[deirdre]

@deirdre . How have you not heard truthers complaining about how according to the official version all skyscrapers are weak and unsafe?

no. maybe you can link me to some of those comments.

 

[Abdullah]

@deirdre i didn't collect them them. So I have no evidence to present.

 

[deirdre]

@deirdre i didn't collect them them. So I have no evidence to present.

well if that is:

one of the biggest drivers

i'm sure you can google me a few examples.

 

[Mendel]

@Mendel because it's really dumb and dangerous and easily fixable. The Towers didn't have this issue.

How often does it happen that 3 columns in a skyscraper collapse? And what exactly was the danger?

How "easy" is this to fix, actually?
And how did the towers not have this issue, they collapsed even sooner after the fires broke out than WTC7 did?

And why stop at 3 columns? Why not demand for 5 or 7 or half of all columns?
And would that not double the cost of every newly constructed building, while only rarely being of use? So that it would be much less expensive to occasionally incur the loss of a building (borne via insurance premiums) than to build everything to your arbitrary standard?

 

[Mendel]

How have you not heard truthers complaining about how according to the official version all skyscrapers are weak and unsafe?

With regard to WTC7, the main complaint by truthers seems to have been that the FDNY stopped fighting the fires at some point; that's where their conspiracy theory attaches.

The idea that WTC7 was "weak" justifies the FDNY decision to not fight the fires, and removes the need for a conspiracy theory, which is why I haven't seen any truthers propose this.

The collapse of WTC7 was not dangerous (to humans) because of this decision.

 

[Abdullah]

@Mendel look at how a mere antenna mount on the Towers saved thousands of lives.

The NIST isolated core models did not converge for the worst case damage scenario. Yet their global models did. Think!

 

[Mendel]

@Mendel look at how a mere antenna mount on the Towers saved thousands of lives.

The NIST isolated core models did not converge for the worst case damage scenario. Yet their global models did. Think!

You avoid answering my questions, or responding to the points I made in my big post, so I conclude that this is not a conversation, and I'll drop out.

(Metabunk policy asks you to state your points plainly, and to not talk in riddles or hints.)

 

[benthamitemetric]

It feels like this thread is spiraling into an abstract discussion of vague claims about the NIST report that are not tethered to reality. In Chapter 14 of NIST NCSTAR 1-9, there is an extensive summary of how NIST evaluated the overall safety of WTC7 and NIST's recommended revisions to the building code given NIST's findings about its probable mode of collapse. Those recommendations have been widely debated in the engineering community for the last 15 years, and NIST even has a website dedicated to tracking their implementation.

Importantly, NIST found that WTC7 was generally prone to classic progressive collapse due to the removal of column 79 between the floors of 11 and 13. As a result, one of NIST's recommendations was that structural systems be expressly designed to prevent such progressive collapses, and NIST even presented a model building code to address that point (see Section 5.1 of NIST NCSTAR 1). NIST's recommendations to that end have been adopted into the International Building Code, as well as many local codes, including the NYC Building Code, Chapter 16 of which was amended in 2008 to specifically to include, via the Key Element Analysis process, design requirements intended to prevent progressive collapses of tall buildings.

So, contrary to the vague supposition in this thread, NIST's findings were taken very seriously by the professionals who deal with these issues every day. It was not lost on any of the relevant professional bodies that NIST concluded that WTC7 was prone to progressive collapse. As Mendel notes, taking those findings seriously involved a cost/benefit analysis, which was undertaken by multiple building code councils and other professionals over many years. Perhaps those specialists erred in their ultimate changes and there are still overly risky designs being built in certain places in the world. I'm not sure if navel gazing in this thread by people who are seemingly ignorant that these things were all considered in depth over ten years ago is going to address that, however.

(As a side note, NIST's finding re WTC7's progressive collapse vulnerability likely formed the basis for the denial by the NTSB's legal counsel of the public release of NIST's entire model, which denial was widely met by truthers with much gnashing of teeth. If you put yourself in the shoes of someone who takes this seriously, however, you can understand why the government would not want to release to the public a full, ready-made suite of analytical models that could potentially be used by bad actors to identify similar progressive collapse vulnerabilities in other tall buildings (and hence would withhold such models on national safety grounds). The truthers who requested such models never exercised their right to appeal the denial into federal court, however, so we will never know for sure the exact rationale for the denial.)

 

[Abdullah]

@Mendel het wait! I thought i was answering your questions but let's try again:

In your long post you asked

How often does it happen that 3 columns in a skyscraper collapse?

Rarely so far. But there are not that many skyscraper-years to choose from.

And what exactly was the danger?

The danger is of two kinds
1. Bringing down an entire building is made simple Eg: three bombs.
2. Things in close proximity can fail simultaneously for the same reason eg: plane crash

How "easy" is this to fix, actually?

1. The solutions to the problems require little additional material and cost
2. You can add diagonal braces at intermittent floors that redistribute loads from columns.
3. Floor collapse due to fire was avoided in the Twin Towers by use of floor connections that were fairly strong in tension

And how did the towers not have this issue, they collapsed even sooner after the fires broke out than WTC7 did

They were hit by planes. As a result there were
1.multiple columns severed and
2.insulation destroyed.

And why stop at 3 columns? Why not demand for 5 or 7 or half of all columns

We stop when we reach a substantial fraction.

And would that not double the cost of every newly constructed building, while only rarely being of use?

Not necessarily, see the answer to your 3rd question.

So that it would be much less expensive to occasionally incur the loss of a building (borne via insurance premiums) than to build everything to your arbitrary standard?

As mentioned in the answer to Q2, human life is at very real risk And as mentioned in the answer to Q3, it is not that costly.

 

[Abdullah]

So, contrary to the vague supposition in this thread, NIST's findings were taken very seriously by the professionals who deal with these issues every day.

My poorly srated point was that debunkers seem to rarely acknowledge that there was something seriously wrong with the building. (and we're going off topic).

 

[Thomas B]

NIST found that WTC7 was generally prone to classic progressive collapse due to the removal of column 79 between the floors of 11 and 13. As a result, one of NIST's recommendations was that structural systems be expressly designed to prevent such progressive collapses,

This is incredibly useful, thanks. I looked at Chapter 14 and it is as you say. In the future, when discussing this with truthers I will emphasize that until 9/11 buildings like this were not designed to withstand progressive collapse and it's therefore to be expected that they'll have vulnerabilities like this.

Indeed,

you can understand why the government would not want to release to the public a full, ready-made suite of analytical models that could potentially be used by bad actors to identify similar progressive collapse vulnerabilities in other tall buildings (and hence would withhold such models on national safety grounds).

Still, it's all a bit troubling. In Chapter 14, they also mention that a single "blast event" (p. 624) could have brought the entire building down.

To bring this back on topic, I wonder if Kostack's model does in fact identify the vulnerability that NIST has wisely not released. And whether it suggests that buildings like WTC7 have a few isolated vulnerabilities or pretty much all columns are "criticial" in the relevant sense.

Basically, I'm asking whether Kostack's model (or something like it) lets us calculate the probability of WTC7 collapsing under the condition of an uncontrolled fire after X number of hours.

 

[Abdullah]

@Thomas B I discussed this here already, but I will repeat myself: it seems that his simulation has all columns from 76 onwards failing at the beginning

 

[benthamitemetric]

This is incredibly useful, thanks. I looked at Chapter 14 and it is as you say. In the future, when discussing this with truthers I will emphasize that until 9/11 buildings like this were not designed to withstand progressive collapse and it's therefore to be expected that they'll have vulnerabilities like this.

Indeed,

Still, it's all a bit troubling. In Chapter 14, they also mention that a single "blast event" (p. 624) could have brought the entire building down.

To bring this back on topic, I wonder if Kostack's model does in fact identify the vulnerability that NIST has wisely not released. And whether it suggests that buildings like WTC7 have a few isolated vulnerabilities or pretty much all columns are "criticial" in the relevant sense.

Basically, I'm asking whether Kostack's model (or something like it) lets us calculate the probability of WTC7 collapsing under the condition of an uncontrolled fire after X number of hours.

Kostack did not perform any fire simulation; he merely assumed the failure of certain components and then his model provided a dynamic analysis of what would follow. I would recommend reaching out to him via his youtube channel if you have any questions on his model's parameters. I assume that his model is only a very high level approximation of the structure of WTC7 and thus the collapses it outputs are only very rough simulations that likely would not be sufficient for truly evaluating the dynamic effects of removing certain structural components for actual engineering applications. (For example, you likely could not use the software on which Kostack relies to perform the Key Element Analysis required to build a high rise in NYC; you'd need to perform a more granular and exacting analysis.) I know Kostack does read metabunk from time to time, so you're probably more likely to get a response if you reference this thread.

 

[Thomas B]

I assume that his model is only a very high level approximation of the structure of WTC7 and thus the collapses it outputs are only very rough simulations

I mentioned this on another thread (and that might be a better place to address it) but, since, at the end of the day, Kostack's model is only an approximation, can't we simplify it even further? I would like to see a load path diagram of a simple structure that can pull itself down like Kostack's model does (and WTC7 did), but, of course, stand up under reasonable gravity and wind loads.

I don't need something that can serve as the basis for "truly evaluating the dynamic effects of removing certain structural components for actual engineering applications". I just need something to help explain the basic engineering principle at work: the way a structure responds to loads and redistributes them when structural elements are removed.

Like I say, the principle should be obviously different from the way we easily understand the collapse of a house of cards. Or we need a really good way of explaining the wisdom of building a skyscraper like a house of cards, e.g., that once the dead weight is factored in and scaled up, there's no reason for much stronger connections (which would also be costly implement).

Stronger connections are, of course, one of the design changes that NIST proposes in the chapter @benthamitemetric drew attention to. So maybe that is actually the way to go?

 

[Mendel]

Thank you for your reply!

Rarely so far. But there are not that many skyscraper-years to choose from.

"Not that many" is subjective. There are well in excess of 5000 skyscrapers >150m in the world, and they weren't all built yesterday.

Danger is a product of the likelihood of an event occurring, and the consequences (loss of life etc.) of that event. If the likelihood is low, the danger is low.

The danger is of two kinds
1. Bringing down an entire building is made simple Eg: three bombs.
2. Things in close proximity can fail simultaneously for the same reason eg: plane crash

It's not "simple" to place 3 bombs inside a building. For example, the WTC was bombed in 1993, and it didn't fail.

The Murrah Federal Building in Oklahoma City was bombed in 1995, it did not suffer progressive collapse, but the loss was nonetheless great.

1. The solutions to the problems require little additional material and cost
2. You can add diagonal braces at intermittent floors that redistribute loads from columns.
3. Floor collapse due to fire was avoided in the Twin Towers by use of floor connections that were fairly strong in tension

I would like to see this demonstrated before I believe it.

They were hit by planes. As a result there were
1.multiple columns severed and
2.insulation destroyed.

Yes. So, as the "simultaneous event" goes, if WTC7 had not collapsed, we'd have saved 33% of the buildings, 20% of the office space, and none of the lives that were lost in the event.

We stop when we reach a substantial fraction.

That's evading the question, because to define "substatial" is the point here.

As mentioned in the answer to Q2, human life is at very real risk

Is it real, though? When it takes hours for the collapse to happen? and compared to the other ways lives are put at risk daily, that are more likely to occur?

My main point of contention, though, is my opinion in post #27 that most truthers don't actually care to make that point, because it does nothing for their conspiracy theory.

To point at something that you did not expect to happen is an easy way to monger outrage, and conspiracy theories ride in on them. The mature approach is to research what the expectations should actually be, based on historic records, and then think about where decision makers with limited resources should allocate them (funding X always means not funding Y), and then examine what decision makers did actually do (as @benthamitemetric has presented). In many cases, that makes the outrage evaporate. (There are counterexamples.)

 

[Abdullah]

There are well in excess of 5000 skyscrapers >150m in the world, and they weren't all built yesterday.

I suppose that's subjective then. The collapse of two 28 year old skyscrapers was enough to change the world.

It's not "simple" to place 3 bombs inside a building.

Nor is it to hijack four planes and fly them to three different locations.

The Murrah Federal Building in Oklahoma City was bombed in 1995

And underwent a progressive collapse.

>The bomb's compression wave caused the fourth and fifth floors to shear up and off their columns and collapse onto the third floor. Floor 3 was connected to the main transfer beam, and pulled it inwards when Floors 4 and 5 fell on it. This caused all of the vertical columns on the southern perimeter that were connected to the transfer beam to collapse as well, along with any floor sections that depended on those columns for vertical support.

https://en.wikipedia.org/wiki/Progressive_collapse

I would like to see this demonstrated before I believe it

For the diagonal bracing of columns NCSTAR1-6 p.168

As for the second point, the collapse sequence of the three towers speak for themselves

if WTC7 had not collapsed, we'd have saved 33% of the buildings, 20% of the office space, and none of the lives that were lost in the event.

You're missing the point. If a plane had flown into WTC7 and severed just a few columns, thousands could have died within seconds.

to define "substatial"

Using s large fraction of the axial force capacity in the remaining columns

Is it real, though? When it takes hours for the collapse to happen? and compared to the other ways lives are put at risk daily, that are more likely to occur?

As already mentioned, it does not necessarily take hours

 

[Gamolon]

@Mendel because it's really dumb and dangerous and easily fixable. The Towers didn't have this issue.

Should this have been found to be point of failure during the design? If so, how would engineers determine that?

 

[Thomas B]

it seems that his simulation has all columns from 76 onwards failing at the beginning

I've been watching the clip from 3:59 in slow motion, and I don't understand what is going on. Can someone walk me through this? It seems like there are failures happening spontaneously all over the place. Do they really all begin with a single failure? Can they all be traced back to a single failure? Where? And which is column 79?