The 9/11 Forum

All considerations of FOS depend on a structure that starts out intact, and take into account design loads up to a defined maximum level of catastrophic stress (typical example being maximum wind loads up to some defined wind speed, or a maximum seismic activity) - and not beyond.

All such considerations are off the table if you exceed these maximum design forces, OR if you cut out a major portion of the structure in one go - as the plane impacts did.

Similar thing with fire resistance: Fire ratings are typically predicated on reasonable and normal assumptions of maximum fire scenarios, and may well not assume the stripping of fireproofing over major areas, the total failure of sprinklers, or the concurrent starting of intense fires on several floors and over large areas.

So from a design perspective, a plane crash with full fuel load is clearly and very far outside of the parameters that you could possibly design for, and it is an open question if such events should even be factored in. So I don't see the designers of the twin towers very much at fault or liable just because they did not design for every possible way to exceed design limits (note the implied paradox). To every building strength there is a force, however rare, that will overwhelm it. No building can ever be made indestructible. The ancient egyptian pyramids being obvious exceptions - with equally obvious problems regarding their appeal and usability for office work or living.

What if the buildings were secretly CDed with tens of thousand of charges - would anyone ask for future highrises to be built such that they can't be taken down with tens of thousand of charges? Nonsense.


The interesting building is WTC7, because it apparently succumbed to fires only, with the loss of sprinklers being the only thing that came on top of "usual", designed for, office fires. If I understand correctly, NIST identified a particular vulnerability that wasn't taken into account for in the applicable building codes, namely the effect of expansion (and contraction) of long beams under fire on truss connections. And then there are a few peculiarities that SanderO pointed out that seem to be too close to being single point of failure vulnerabilities.


What ozeco wrote: Whether or not NIST identified correctly the actual drop of water that proverbially made the barrel run over, or not, doesn't affect very much those who in the future design highrises: They will be very much aware of the problems with long trusses,open office spaces and naked steel protected by light-weight fireproofing only, and take them into account.

Well, very high buildings with 10 000+ occupants should be build as strong as possible. FOS of only 2 is Russian Roulette.

"They will be very much aware of the problems with long trusses,open office spaces and naked steel protected by light-weight fireproofing only, and take them into account."

Yes, but

1) we are not trying to teach the community here, we are just fixing NIST's errors and by errors I mean the total failure in the most basic question "what gave way first" because this is the most fundamental question of any investigation

2) it won't help when major load bearing systems have low FOS, remember everyone with the knowledge can identify a vulnerable skycraper, bring in 3 8kg HMX charges and collapse the building within a minute (yes, that quickly)

uglypig wrote:Well, very high buildings with 10 000+ occupants should be build as strong as possible. FOS of only 2 is Russian Roulette.

Ok. Propose a better FOS! What should it be?

uglypig wrote:...
1) we are not trying to teach the community here, we are just fixing NIST's errors and by errors I mean the total failure in the most basic question "what gave way first" because this is the most fundamental question of any investigation

The first thing to give way was the window (or the column section) that was hit by the nose of the plane.
There, fixed that.
Did that help?
No.

Damage accumulated, loads redistrinuted, up to a point where FOS decreased from barely >1.000 to barey <1.000. Whatever this event was, it was one further drop of water that made the barrel run over. Was this drop of water any more essential in running over the barrel than any of the drops that came before it?

uglypig wrote:2) it won't help when major load bearing systems have low FOS, remember everyone with the knowledge can identify a vulnerable skycraper, bring in 3 8kg HMX charges and collapse the building within a minute (yes, that quickly)

Huh?

Like I said, all concepts of FOS are out the window once you introduce a catasprophe that goes beyond that which you can design against. Such as big fast plane with tons of fuel. Or well you could design against such events, but at the cost of having no windows and precious little office sopace. Think stone pyramid.

Remember, there is a limit to every resource, and there is a limit up to which you can make a building safe from collapse. You can't have total safety. It is impossible.

Ok. Propose a better FOS! What should it be?

FOS of 3 for tall buildings that house more than 10 000 ocupants. No one should be allowed to construct a core structure as weak as the twin towers had.

The first thing to give way was the window (or the column section) that was hit by the nose of the plane.
There, fixed that.
Did that help?
No.

Oh my god. Have you ever heard of any real failure investigation?

Was this drop of water any more essential in running over the barrel than any of the drops that came before it?

Uhm, yes?

eyond that which you can design against

Yeah, 30% increase in FOS for iconic 500m+ buildings is just impossible.

Remember, there is a limit to every resource, and there is a limit up to which you can make a building safe from collapse. You can't have total safety. It is impossible.

So we should gave up trying? Wow.

This is no JREF, your walls of sophistry don't mean anything here. Deal with it.

uglypig wrote:Well, very high buildings with 10 000+ occupants should be build as strong as possible. FOS of only 2 is Russian Roulette....

I am very clear that it is your opinion that, given the advantage of 20/20 hindsight, factors of safety should be higher for iconic buildings. Your claim that it is "Russian Roulette" is a false implied reference to the probabilities of failure. The reason for failure of the WTC buildings was an unpredicted and not allowed for attack. Without that attack the collapses would not have occurred. We cannot retrofit higher FOS's to the WTC towers. The legitimate purpose of identifying the alleged FOS weakness is so we can learn for future buildings. I have hinted several times as to where that allowance for future buildings will lie. Primarily it lies with future owners and future engineers/architects designing for those owners. To what extent it also lies with regulatory authorities we could also discuss.

In another post you have implicitly rejected the underlying principle - the question of "How much safety margin can we afford within commercial realities for this project?" That question is central to all planning for big projects and cannot be simply rejected. You may be correct that higher FOS is desirable but it has to be decided in the full context of regulatory requirements and commercial realities. And, as an engineer, I doubt that focussing on the single issue of FOS is the best way to achieve a higher level of structural safety.

uglypig wrote:..."They will be very much aware of the problems with long trusses,open office spaces and naked steel protected by light-weight fireproofing only, and take them into account."

Yes, but...

OK - so far we are on the same sheet of music.

uglypig wrote:...1) we are not trying to teach the community here, we are just fixing NIST's errors and by errors I mean the total failure in the most basic question "what gave way first" because this is the most fundamental question of any investigation...

Which takes us right back to the start of this recent attempted discussion with Major_Tom. That is the belief that M_T adheres to stubbornly and you are now following. The belief that error in a detail makes the NIST project a total failure. The issues I have raised over that false assumption are still unanswered. And restating the belief loaded with emotive terminology does not make a persuasive argument. For the Twin Towers NIST identified that the "impact and fire zone" gave way first. The challenge to Major_Tom and now to you is to demonstrate why it is relevant that bolt "A" failed before weld "Z". I have set out the reasons why I think that it is not relevant in multiple previous posts.

If you simply wish to retain as your opinion that the detail is important be my guest. I have no objection to you holding that opinion. But if you want to persuade me to share your opinion......

uglypig wrote:...2) it won't help when major load bearing systems have low FOS, remember everyone with the knowledge can identify a vulnerable skycraper, bring in 3 8kg HMX charges and collapse the building within a minute (yes, that quickly)

This statement is a mix of 20/20 hindsight about a past event which cannot be changed and a wish that future buildings be protected against attacks which may occur in the future and must be protected against even if they cannot be quantified. FOS is only one aspect. Another reality is commercial viability. A third is regulatory constraints. So I suggest you need to get clear what your concern is - disagreement with the past OR proposals for the future. And, to what extent do you claim that the lessons of 9/11 have not been learned by the industry world wide.

uglypig wrote:...This is no JREF,...

How true. The noise levels here are much lower. The atmosphere is troll free.

BUT: The advantage of this forum is that false arguments have nowhere to hide.


...and the disadvantage is....

Ok, the actual reason for the biggest construction failure in modern is history is not important. Got it!

uglypig wrote:Ok, the actual reason for the biggest construction failure in modern is history is not important. Got it!

Since it wasn't a construction failure your suggestion goes no-where.

The actual reason for the WTC1 and WTC2 collapses was accumulated damage. There are two main camps of opinion as to the components of damage. Viz:
1) Aircraft impact plus fire damage; OR
2) Aircraft impact plus fire damage with some assistance from human demolition activity.

"1)" Is well attested by evidence and multiple sources of professional analysis.
"2)" Has had lots of input from a small number of quite vocal claimants. To date none have put forward a reasoned supportable hypothesis.

I am unaware of any claims that it was a construction failure.

Have fun.

Ozzie,
I would assert that the Empire State building and the Sears tower, both extreme tall buildings and one built just after the twin towers would not have collapsed if subject to the same plane strikes. They wouldn't collapse because their design was different... no tube in tube with long span (rather light IMO) truss supported column free office floors. Building seven would not have collapsed if it was a conventional frame without setting it atop a sub station with its core sitting on top of 3 transfer trusses and several cantilever girders supporting the north columns line.

These were design / developer / architectural choices which were permitted by the NYC DOB with an arrangement which allowed PANY to receive waivers on NYC DOB code requirements.

My contention is, like the Ford Pinto, the product could perform as expected under normal conditions, but not from out of *spec* conditions which in the case of the towers were plane strikes (somewhat predictable since it had happened to the ESB as a result of an accident being that the towers were quite close to 3 very large busy airports). In fact, the designers DID consider plane damage... but claimed to have forgotten to account for fuel loading (hahahahaha).

To me this represents a product liability issue(s) and a design and construction failure.... a disaster waiting to happen... a sort of ticking time bomb. I don 't think a Cesna would have done it... but I also don't think that super high speed was required nor fully loaded fuel tanks. I suspect a large jet with normal fuel fuel on board would cause enough structural damage and begin massive fires, disable the sprinkler system, over come the rather flimsy FRP, cause voltage spikes and blow out transformers in the tower and up stream....

The placement of diesel tanks replenished from a 20,000 gal tank in the basement running gen-sets above the Con Ed sub station within the transfer trusses supporting the core with massive supply air grilles likewise represent a series engineering, architectural and developer choices which were negligent and irresponsible and another ticking time bomb. Another series of Ford Pinto-like decisions which no one was held accountable for.

And of course NIST, FEMA, ASCE, AIA, 911 Commission, Perdue U, Pop Mechanics, PBS, AE911T and others fall failed to identity the defects / decisions noted above and demand accountability... or at least an investigation into the above allegations. For various reasons these groups produced more deception and smoke and mirrors avoiding the truth about part of what happened on 9/11.

SanderO,
I comprehend;
A) the direction you want to take leading to a joint accountability for the consequences of the WTC collapses; AND
B) Your string of supporting judgements all of which are aspects which did contribute to the collapse. However your estimates that those factors would have contributed (or not contributed) are all subjective and not ones where I could guess the actual amount of contribution any better than you do.

I recognise that you may have in mind employment sanctions against those you judge to be guilty rather than inclusion in a civil action in tort for damages. However testing the idea against a "moot court" setting is a useful device for judging the merits of such a claim. The law on contributory negligence differs between jurisdictions. But, in general, when confronted by an undoubted source of the primary negligence the reduction in damages resulting from a finding of contributory negligence tends to be quite low. About half of "pro-rata of causation" as a quick guess based on typical low scale civil claims e.g. motor vehicle accidents. What it would be in a US court for such a large claim I haven't a clue. And that is when the contribution is proven which is not so in this case at this stage of the development of your claim.

Despite your wish to see factors such as the waiving of code requirements in the most evil light that is not the likely outcome of a court case where both sides get to put their evidence and reasoning. I don't see these contributory negligence claims ever going before a court but multiple lines of defence would seem to be available.

And all of that before we even get to the political considerations involved in putting US companies up alongside the terrorists as joint perpetrators.

Political considerations tend to be swayed by the amount of influence the concerned parties have in the political arena. And the political clout of the truth movement is not very much. So whether or not your suggestions can be supported at law - which I doubt - I don't see where there would be political support for an action which would easily be represented as prosecuting US citizens as joint terrorists. Sure employment sanctions are easier to impose politically - scapegoating is normal practice in the political arena.

Sorry that my argument is so loosely constructed but the issues do not lend to concrete conclusions.

Ozzie,

You are jumping ahead a bit here... especially conflating the percentage of contribution of the damage to victims between the terrorists and the *project developer team*.

First, I would like to establish accountability here... regardless of the dollar value of the personal damages. Those sorts of calculations when loss of life etc. are concerned are a mystery to me. But it is my belief that those involved in creating those towers need to be held accountable for their *mal-practrice* or in the case of PANY and the NYC DOB abuse of trust of the people. It may not mean much that the DOB permitted the PANY to reduce the design loads of the floor system. The reason for the request is obvious - to save weight and money. To my way of thinking this was contributory to the collapses.

The decision to build a skyscraper (Bldg 7) over the Con Ed sub station was nothing short of greed... the acquisition of the air rights to create more rentable office real estate. The engineers, in my opinion demonstrated hubris and lack of foresight with the cooperation, and encouragement of the Guiliani Administration for siting the EMC on the 23rd floor with 20,000 gal diesel tanks in such close proximity to a massive power sub station. The DOB, Planning and Zoning Boards rolled over because they are suck ups to the real estate industry. All of these decisions were extremely ill advised without consideration to the low probability of a terrorist hijacking a plane and flying it into bldg 7.

The *building officials* in NYC can be extremely *choosey* about what proposals they accept making owners jump through hoops when they want or not as the case may be. The destruction of the WTC should have brought to light the gross mis conduct of the players associated with its erection all driven by ego and money. Yet when they came down, it was the victims and the people which have taken it on the chin while the interests identified above *skated* and even benefited from the event.

That's not my idea of accountability.

Sorry to pile up on what ozeco wrote, but...

uglypig wrote:FOS of 3 for tall buildings that house more than 10 000 ocupants. No one should be allowed to construct a core structure as weak as the twin towers had.

Why 3? Why not 2.5? Why not 4?
What are your reasons? Have you considered aspects of costs, usability, and remaining risks?
How do you know that a FOS of 3 would have saved the towers? What would have worked out different? My gut feeling tells me that the towers would merely have stood longer until collapse. But that is just gut feeling. I wonder if you have anything more than gut feeling?

(And for good measure: Would M_T's visual observations help us make this determination which FOS would suffice?)

Oh, and still: Once you crash a plane into a building, dump 10,000 gallons of incendiary and locally take out fireproofing and sprinklers, any pre-impact FOS is off the table. As a global measure, it only makes sense in the context of an intact building under loads within the designe constraints. So adjusting a single factor of global FOS doesn't fundamentally change the game. It's instantly gone and reduced to an unknown after crash.

uglypig wrote:

The first thing to give way was the window (or the column section) that was hit by the nose of the plane.
There, fixed that.
Did that help?
No.

Oh my god. Have you ever heard of any real failure investigation?

Was this drop of water any more essential in running over the barrel than any of the drops that came before it?

Uhm, yes?

I guess we won't agree here.

uglypig wrote:Yeah, 30% increase in FOS for iconic 500m+ buildings is just impossible.

Strawman. That's not what I said. Sure you can increase FOS by 30%, or 100%, or perhaps 1000%. What I said is: None of that makes a building indestructible. Nothing ever will. You have to realize that a certain residual risk will always remain,. You must accept that, and balance it against other considerations such as cost.

uglypig wrote:

Remember, there is a limit to every resource, and there is a limit up to which you can make a building safe from collapse. You can't have total safety. It is impossible.

So we should gave up trying? Wow.

Yes, absolutely. We shouldn't even start to try making building totally safe from collapse. It is impossible. Go for the possible, and keep an eye on your resources. Don't go for the impossible, your resources are not enough for that.

Just a few points commented:

SanderO wrote:...
My contention is, like the Ford Pinto, the product could perform as expected under normal conditions, but not from out of *spec* conditions which in the case of the towers were plane strikes (somewhat predictable since it had happened to the ESB as a result of an accident being that the towers were quite close to 3 very large busy airports). In fact, the designers DID consider plane damage... but claimed to have forgotten to account for fuel loading (hahahahaha).

A) Plane strikes are either within the specs, in which case they would constitute "normal conditions" from a design point of view, or they are outside of specs, in which case they can't be expected to be taken care of by the design.

B) No, the designers did NOT consider plane damage - not as design spec at least. They modeled a plane strike in a rather simplified model as an afterthought, by slicing out perimeter columns as wide as a 707 wingspan, ran some standard calcs, and found the towers would not collapse immediately. And they were right.

C) They did not "forget" to account for fuel loading - they determined it was too complex of a problem to compute when they thought about it in the 1970s. And they were right. The overriding consideration in that case of large fires would be swift egress of occupants - and we see how that worked out: Pretty well for everybody below impact, horrendously gone wrong for everyone above.

SanderO wrote:...I also don't think that super high speed was required nor fully loaded fuel tanks. I suspect a large jet with normal fuel fuel on board would cause enough structural damage and begin massive fires, disable the sprinkler system, over come the rather flimsy FRP, cause voltage spikes and blow out transformers in the tower and up stream....

uglypig thinks FOS=3 would have saved them. Do you agree? Would FOS=3 also have saved against a 747 crash at high speed?

SanderO wrote:The placement of diesel tanks replenished from a 20,000 gal tank in the basement running gen-sets above the Con Ed sub station within the transfer trusses supporting the core with massive supply air grilles likewise represent a series engineering, architectural and developer choices which were negligent and irresponsible and another ticking time bomb. Another series of Ford Pinto-like decisions which no one was held accountable for.

I obviously am not familiar with all the detailed results of investigation in this forum, but has it beenm determined that any of the factors you list there were actually and necessarily at play in the collapses? My understanding of NIST's scenario is that neither diesel nor the transfer truss solution was essential for collapse initiation. Not sure how the transfer trusses played a role in NIST's collapse progression (I am far from being well-read on WTC7, so please construe these questions as honest quests for summary information for a relative newbee, perhaps a link or two will do, and a short paragraph, for starters)

SanderO wrote:Ozzie,

You are jumping ahead a bit here...

Am I? Let's go through the steps a bit slower in case I am.

SanderO wrote:...That's not my idea of accountability.

So what is your "idea of accountability"? What do you mean by "accountability"?

We review what they did and if we find that they fell short of some standard:
A) We tell them they were naughty boys? OR
B) We impose some sanction on their employment; OR
C) We consider legal action in the Civil jurisdiction for damages; OR
D) We consider legal action in the criminal jurisdiction leading to punishment?

...and you have already predicted that their conduct falls short of your standard. So, whilst you are at it telling me what you mean by "accountability", why not define the relevant standard you are applying.

Oystein wrote:...Yes, absolutely. We shouldn't even start to try making building totally safe from collapse. It is impossible. Go for the possible, and keep an eye on your resources. Don't go for the impossible, your resources are not enough for that.

That reminds me of an old explanation of the reason we employ engineers.

Anyone can build something that wont fall down. It may take a bit of trial and error....

We employ engineers to make sure it suits the purpose, is strong enough for that purpose and cheap enough to suit the client. And do it without "trial and error"

So sufficient strength, adequate safety and at a price the client can afford.

BTW This claim for "totally safe" reminds me of the discussion of infinitely strong moment frames on "another forum" There is no such thing in either case.