The 9/11 Forum

Oh, it's right there, I need to learn to read.

Dr. G wrote:In February 1975, a fire occurred in WTC 1 that affected floors 9 to 19 and led to a review of the adequacy of the existing thermal insulation in the entire WTC. The need to upgrade the passive fire protection in the Twin Towers was finally addressed in 1995 when, after yet another study, it was decided to apply a 1½ inch thickness of an asbestos-free spray-on mineral fiber fire protection material to selected steel surfaces. Thus, between 1995 and 2001, thermal protection was upgraded specifically on 18 floors in WTC 1, including floors 92 to 100 and 102; and on 13 floors in WTC 2 including floors 77, 78, 88, 89, 92 and 97. (See NIST NCSTAR 1-6A page xxxvii).

Not an exact match, but pretty close and arguably close enough. It was in another post where he opined that the introduction of a surreptitious formulation could be accomplished with as little as 1-2 hands-on people having any knowledge of the picture broad enough to connect all the dots and see their role.

As I recall, perfectly plausible to me, and frankly my opinion on this matter might carry more weight than usual. One of my past occupations put me in intimate contact with people whose day to day job was mixing, casting and curing solid-fuel rocket motors utilizing the very formulations Dr. G describes. I have little doubt that the formulation could be determined by a single person, and mixing done likewise by a single person, for a job of the scope proposed here. No problem. Only the former person even need know what's going in the mix, and then no need to know why.

I caution people never to limit the possibilities to their own imagination. There's a reason not a one of us is employed in the intelligence and special operations field. Right?

It is an interesting hypothesis. I am certainly not aware of a "truther side" claim which is as well thought through --- most being limited to a single issue technical claim with no attempt at fitting into a complete hypothesis and context.

Without committing myself to an extended debate (at this stage anyway ) there are two issues I will raise:

First is a procedural matter. The work is an hypothesis for discussion - not a claim presenting for rebuttal. As such it does not trigger the burden of proof issues that a claim would involve. Were it a claim I would take the opposing side and insist that the claimant bear burden of proof.

Second is the scope and intent of these pre placed materials. There seem to be two scenarios viz:
1) It was pre placed as preparation for a stand alone demolition at some future stage.
2) It was pre placed with the hijacked aircraft scenario in mind.
(Strictly to avoid false dilemma I suppose we should have 3) It was pre placed with some other scenario as the "cover story" AND "trigger" - my imagination fails me in suggesting what that scenario could be.)

Now if it was "1)" firing the stand alone would blow the cover plus, to be plausible, we need at least a technical plan of what collapse mechanism was to be triggered. AND without the benefit of post 9/11 20/20 hindsight. One possible point of contention could be whether the mechanism deliberately sought to trigger ROOSD. i.e. is it reasonable that the inbuilt vulnerability of the Twins would be pre identified and deliberately used. I cannot put a probability on that one. Either way.

If however it was "2)" there are a couple of issues as to long term prior awareness of the hijack plan and collaboration between the perchlorate users and the 'plane plan leaders.

And it still raises several of the more strategic questions such as:
A) Why complicate the hijack plan?
B) Why do it since it was technically redundant (Some 20/20 hindsight issues there but...)
Probably a few more - I may put brain in gear to think it through ... but be warned I'm "forummed out" on discussing 9/11 technicalities. All recent technical discussion seems to have been on sidelines and red herrings - certainly on "that other forum".

NOW you're talking! You're getting to the meat of it!

I wish I had time to respond, but I blew my allowance today on the prior posts. If I can somehow manage to ride the mad bull through the streets of Pamplona tonight (that is to say, make Microsoft's coded UI test framework behave like a civil state machine), maybe tomorrow I can give a reply to your most thoughtful post.

OneWhiteEye wrote:One of my most oft-used citations. Guess what happens when a skyscraper is "undetectably out of plumb"? People like Leslie Robertson demand a rework.

Thanks for the link!

OneWhiteEye wrote:You're overlooking the effectiveness of placement. What is the minimum energy required to catalyze the total destruction of the towers? In my opinion, negligible, at least as compared to what is typically bandied about - if strategically applied. There is a difference between possible, probable, and high confidence, I'd admit. And, I'd further admit no one knows the mechanics perhaps as well as is generally assumed. All the same, I suspect the energy contained in a couple of tanks of acetylene, or in a few hundred pyro bolts (firecrackers, relatively speaking), are enough to bring it to the threshold of possibility.

The beauty of the AP is that it can be all over the place; ...

I think we are talking about two different things here. SanderO was musing about extra incendiaries aboard the planes - an off-topic here, on which I followed him. You can't place any substances strategically and effectively by crashing a plane.
The on-topic scenario of applying AP by hand directly on the steel - sure, that can work

OneWhiteEye wrote:I always thought it was funny that some of the same people who'd calculate thousands of tons of explosives would be needed to CD the building could then turn right around and claim none were required. Not saying you're doing that, you're not, but it is funny.

Well I have done calculations like this, but only for those folks who doubt that enough potential energy was available for total collapse progression and "pulverisation". If someone doubts that gravity could crumble all the concrete, i.e. do all the destruction not essential for CD, and they base this on gut feeling, then they must be assuming that additional explosives worth at least, say, 50% of the PE must be added, to make a significant difference, or perhaps many times the PE. And that works out then to dozends, if not hundreds, of tons of explosives per tower.

Oystein wrote:

OneWhiteEye wrote:...The on-topic scenario of applying AP by hand directly on the steel - sure, that can work ...

Not so fast there Oystein.
Sure "that can work" is correct if you limit your meaning to putting the material in place - and presuming you can satisfy all the strategic ("Why do it?"), logistic and security challenges.

BUT how do you initiate it? Which begs the question of where did you apply it (plus a few more hurdles).

One proposal was put it in the fireproofing - that could facilitate it being used to cut floor joist lower chords - which happens to be my identified critical point from a few years back.

But how do you keep it intact on said lower chords when you are going to crash a plane through the area?

And the 20/20 hindsight overview - it wasn't necessary anyway.

Hence my identification in my previous post of the need to be clear what scenario we are discussing. If it is some abstract hypothetical then the rules can be a lot easier. BUT if it is a pseudo claim as to what could actually have happened on 9/11 the reality is it wasn't needed so we are discussing at most a redundant CD which still had to stay hidden in the mess of what actually happened.

(My framework assumptions should be self evident. Subject is Twin Towers collapse; three possible stages where CD assistance could be provided. viz (1)pre-weaken core; (2) assist collapse initiation and (3) assist collapse progression. (3) not needed and (1) merges with (2) )

Oh this is interesting with respect to the transfer trusses of building 7:

"Precisely because of that leverage, a margin of safety is built into the standard formulas for calculating how strong a joint must be; these formulas are contained in an American Institute of Steel Construction specification that deals with joints in structural columns. What LeMessurier found in New York, however, was that the people on his team had disregarded the standard. They had chosen to define the diagonal wind braces not as columns but as trusses, which are exempt from the safety factor. As a result, the bolts holding the joints together were perilously few. "By then," LeMessurier says, "I was getting pretty shaky......

The weakest joint, he discovered, was at the building's thirtieth floor; if that one gave way, catastrophic failure of the whole structure would follow. Next, he took New York City weather records provided by Alan Davenport and calculated the probability of a storm severe enough to tear that joint apart. His figures told him that such an event had a statistical probability of occurring as often as once every sixteen years--what meteorologists call a sixteen-year storm"

ozeco41 wrote:Not so fast there Oystein.
Sure "that can work" is correct if you limit your meaning to putting the material in place - and presuming you can satisfy all the strategic ("Why do it?"), logistic and security challenges.

BUT how do you initiate it? Which begs the question of where did you apply it (plus a few more hurdles).
...

Relax, ozeco
My "that can work" wasn't even extended to how to put it in place. The context was "how much extra energy do you need from incendiaries to make a difference?", and the distinction was between "lots and lots if randomly dumped" and "not really that much if placed efficiently". The latter "can work", limited to meaning "you don't need dozends of tons of AP if you can put directly on the steel". No implication intended that there is (or isn't) a feasible method to actually do it.

Oystein wrote:...Relax, ozeco
My "that can work" wasn't even extended to how to put it in place. The context was "how much extra energy do you need from incendiaries to make a difference?", and the distinction was between "lots and lots if randomly dumped" and "not really that much if placed efficiently". The latter "can work", limited to meaning "you don't need dozends of tons of AP if you can put directly on the steel". No implication intended that there is (or isn't) a feasible method to actually do it.

Gotcha.

Remember I'm the (former) military engineer so every time I read these sorts of posts I am automatically working out the "how would I do it".

BTW don't most of these incendiaries have less energy than kerosene?

I've read different things about how much the yield strength of steel is weakened as its temperature rises. Can some cite a definitive source about how heat actually works/ affects steel sections? How extensive or localized can/must the elevated temps be for an observable affect?

For example when you weld to a steel column the area around the well is extremely hot... enough to melt the steel, but there is a gradient as you move away from the weld down to room temps.

In the CitiCorp fix they were welding 2" thick plates to the trusses over the bolted connections. That must have heated those trusses significantly and they were under load at the time. What's the deal with that?

Oystein,

There was probably a typo in the report.. It was meant to read 13KV feeders... that 13,000 volts OUCH.

read up here:

http://www.coned.com/messages/LICReport/Overview.pdf

ozeco41 wrote:...
BTW don't most of these incendiaries have less energy than kerosene?

That was my original point: That if you want to carry incendiaries on a plane to dump them in a building by crashing with the intention of maximizing heat stress and fire damage, the stuff you have 10,000 gallons of aboard already is probably your best choice. Wouldn't make much sense to add other incendiaries. Only exception that I can see would be explosives that go off as you crash.

SanderO wrote:Oystein,

There was probably a typo in the report.. It was meant to read 13KV feeders... that 13,000 volts OUCH.

read up here:

http://www.coned.com/messages/LICReport/Overview.pdf

Ah thx that makes a lot more sense

SanderO wrote:I've read different things about how much the yield strength of steel is weakened as its temperature rises. Can some cite a definitive source about how heat actually works/ affects steel sections?...

It is many years since I did hands on structural work AND even then we paid little attention to temperature - it is a specialised area of structures usually related to fire safety.

That said I did a bit of Googling and found this paper:
http://www.mace.manchester.ac.uk/projec ... erties.htm

From it Figure 7 shows the sort of base information to answer your first question.
http://www.mace.manchester.ac.uk/projec ... igure7.htm
It is for a typical structural steel and, reading it for approximate values, as temperature rises up to 400^oC sees no loss of strength whilst 600^oC sees strength reduced to about 50% and 700^oC reduced to about 25%.

I note that those are the sort of percentage reductions we have seen quoted in the 9/11 forums.

The next few answers are my own judgements so E&OE plus blame age:

SanderO wrote:How extensive or localized can/must the elevated temps be for an observable affect?

The main point would be that only the heated portion of steel is affected. So the "observable affect" would depend on where the heated portion fits into the structure and, therefore, what effect results from weakening of that portion of structure. Situation specific so I cannot give generic examples. One further proviso - probably only of second order impact - the temperature gradients caused by partial heating could also complicate the stress loading arrangements but only in the immediate vicinity of where the heat was applied.

SanderO wrote:For example when you weld to a steel column the area around the well is extremely hot... enough to melt the steel, but there is a gradient as you move away from the weld down to room temps....

Yes - and the heated bit is weakened but the remainder being at ambient temperature means probably not a large effect on overall strength. Still bear in mind the proviso I stated above - the temperature gradient may introduce extra stresses by my guess is that they would tend to be second order.

SanderO wrote:In the CitiCorp fix they were welding 2" thick plates to the trusses over the bolted connections. That must have heated those trusses significantly and they were under load at the time. What's the deal with that?

I haven't a clue as to the specifics however...
Most structural work has a built in safety factor - back in my student and early professional career we only loaded steel to half its (ambient temperature) yield strength. So there is spare capacity for temporary weakening.
Also the welding would only affect portions of the structure which may not be all that critical. I worded that badly - they were reinforcing so something about the original was less that satisfactory BUT it was probably the bolting NOT the bits bolted.

As I said E&OE

I raise this issue because of how heat would impact a steel column. All stress must *pass through* the cross sectional area of the column. If the column is 3 stories tall but heated at a location say 1-5' above the bottom of the column as it was set about 3' off the floor on top of the column below... the very bottom of the heat column is being weakened by the heat. The length above may remain cold enough to have most of its strength. But that wouldn't matter at all. If the lower 5 feet has lost 50% of its strength that governs how much axial load that column can support.

Again, here is where Factor of Safety or reserve strength becomes a critical factor in the structure to withstand all sorts of weakening. If we assume a FOS of 2... then the entire core heated to 600°C would remove ALL the reserve strength. The FOS is 1... nada. But let's consider that not all the columns were the same cross section. Perhaps the thinner ones would fail sooner from the same applied heat as they larger ones might be able to conduct the heat away from the heat sort. Maybe. If that is the case... could the smaller section buckle before the larger ones?

To me it sounds like it wouldn't take too much to weaken row 500 to the point of collapse. First, only every third floor would need to be *attacked* with AP or whatever heat source was used. Second.. a dead center strike would take out 3 or likely 4 of the columns of row 500 causing the north side of the core to lose about 30-40% of its strength on impact.

How about the notion that some of the columns were destroyed by the plane impact... and several were assumed to be damaged. Does a damage columns lose some of it's strength? Half?
If the columns on the row 500 or 1000 side were destroyed their loss would be proportionately greater than the first or last column in row, 600, 700, 800 and 900. And those corner columns were carry much larger loads than any other core column. Note it was 501 (a corner column) which stood the tallest after the floor collapse. If 3 or 4 row 500 columns were destroyed by the plane impact... it could mean a loss of 20% of the core's axial load capacity. In the 4 center columns of row 500 were destroyed by the plane row 500 would have lost over 40% of its capacity to support the OOS flooring to the north. And with the facade opposite those columns damaged, it likely that partial floor collapse occurred on impact.

Now with heat beginning to work the remaining columns which are now at a much lower safety factor having taken on the axial loads of the destroyed columns from above... are growing weaker as their temps rise. Right away the FOS was well below 2 (perhaps 1.5 or so) with the plane strike affecting 4 of the 8 columns on the north side of the core (Tower 1). Now if these remaining columns lose 1/3 of their strength... they will buckle. it looks like 500° C might be enough temperature to buckle the north side of the core if columns 503, 504, 505, and 506 were destroyed on impact.

The next two columns 502 and 507 lose their strength from the increasing heat that leaves the two strong corner columns 501 and 508 holding up the entire north side of the OOS floors and all those above it. YIKES!

Is it possible to raise the temps of the remaining 4 columns to cause them to buckle? This looks like not as complex a take down as one would think.

SanderO wrote:I raise this issue because of how heat would impact a steel column. All stress must *pass through* the cross sectional area of the column. If the column is 3 stories tall but heated at a location say 1-5' above the bottom of the column as it was set about 3' off the floor on top of the column below... the very bottom of the heat column is being weakened by the heat. The length above may remain cold enough to have most of its strength. But that wouldn't matter at all. If the lower 5 feet has lost 50% of its strength that governs how much axial load that column can support....

Let me initially limit my answer to the key point of this paragraph. It contains a misunderstanding about column strength which underpins much of the remainder of your post.

And my comments are again "top of the head" on subjects which I have not studied for 50years plus.

The strength of a column for our purposes here is the measure of the maximum axial load it can carry. The limit is reached when the column is on the verge of buckling. Once it buckles strength is lost very rapidly - instantaneous for our purposes here. So it is a "trigger" or "threshold" situation.

The theoretical work to determine that strength was done way back 1700's IIRC by Euler.

The main point is that for any given column cross section and presuming constant cross section the strength is inversely proportional to the square of the length of the column. So doubling the length of column reduces its strength to one quarter. Hence (whether we accept the full NIST WTC7 hypothesis or not) the removal of horizontal bracing of column 79 of WTC7 over (say) three floors would result in a ninefold weakening of the column. Based on the raw length factor alone.

Another factor is "E" the elastic modulus. It is linear in the strength equation - double the "E" and you double the strength. And the effect of heat is to modify "E".

There is another relevant factor which is the "end conditions". Columns may be free to rotate at their ends - referred to as "pin-jointed" or they may be fixed so they cannot rotate. By "rotate" I mean free to lean from side to side versus not free to do so. A pin ended column is effectively twice as long as a fixed ended column. And the length is squared. So freeing up the ends of a column to rotate weakens it fourfold.

Go back to our example the strength over one floor is "X" and the ends of the column are(nearly) fixed at each floor level (depends on the detail of the joints)

If we triple the length the strength is reduced by a factor of 3 squared = 9 (Or X/9) we have freed up two levels of "column ends" but that factor does not come into play.

Let us leave the rough outline of theory and go to your situation. If only part of the column is heated we change the elastic modulus which is one factor which has a linear effect on strength (It is on the top side of the equation and not squared or any other power. So a partly heated column becomes two columns joined end for end - one heated and one not heated. (Lets leave the "transition" temperature grading out at this stage for simplicity.) And if the heated bit is at floor level the weakening due to heating could have the effect of turning the "fixed end" of the column into "pin jointed".

The net result is not that the whole column is reduced in strength to that of the weakest part. That is where I think your reasoning goes off track.

Rather the part heated column has a strength part way between the full strength unheated column and a fully heated weakened column. Exactly where it falls between the two is more complicated than we need address at present. ditto the "end effects".

Now with that bit of principle addressed let's see if we can comment on the rest of your post.

SanderO wrote:...Again, here is where Factor of Safety or reserve strength becomes a critical factor in the structure to withstand all sorts of weakening. If we assume a FOS of 2... then the entire core heated to 600°C would remove ALL the reserve strength. The FOS is 1... nada. But let's consider that not all the columns were the same cross section. Perhaps the thinner ones would fail sooner from the same applied heat as they larger ones might be able to conduct the heat away from the heat sort. Maybe. If that is the case... could the smaller section buckle before the larger ones?...

There are too many interacting factors for a simple answer. Let me pick the dominating factor. That is that all these columns are part of a framed structure. And what fails first will be the result of the overall mechanics of the structure where some members have had their "E" (elastic modulus) changed due to temperature. So the thinner ones won't fail faster because they lack the heat sinking of the thicker ones. Rather they may fail first because in the overall scheme of things they are closest to overload and something trips them into overload. That something being a combination of all the factors adding up in the cascade failure mechanism where every structural elements strength has been modified from original design by the effects of raised temperature.

Apologies for the denseness of that. Let it stand for now and see if you have further queries.

SanderO wrote:...To me it sounds like it wouldn't take too much to weaken row 500 to the point of collapse. First, only every third floor would need to be *attacked* with AP or whatever heat source was used. Second.. a dead center strike would take out 3 or likely 4 of the columns of row 500 causing the north side of the core to lose about 30-40% of its strength on impact....

We are getting lost between hypothetical considerations and the reality of what actually happened. So no comment at this stage.

SanderO wrote:...How about the notion that some of the columns were destroyed by the plane impact... and several were assumed to be damaged. Does a damage columns lose some of it's strength? Half?...

If cut it loses 100%, if bent out of line it loses "most" because the bending initiates buckling orders of magnitude easier (At least one decimal order - I would need to refresh my knowledge)

SanderO wrote:...If the columns on the row 500 or 1000 side were destroyed their loss would be proportionately greater than the first or last column in row, 600, 700, 800 and 900. And those corner columns were carry much larger loads than any other core column. Note it was 501 (a corner column) which stood the tallest after the floor collapse. If 3 or 4 row 500 columns were destroyed by the plane impact... it could mean a loss of 20% of the core's axial load capacity. In the 4 center columns of row 500 were destroyed by the plane row 500 would have lost over 40% of its capacity to support the OOS flooring to the north. And with the facade opposite those columns damaged, it likely that partial floor collapse occurred on impact.....

We need another bit of theory here. Let me try for very simple.

Removing a percentage of columns does not reduce the strength of the assembly by that percentage. Stated differently removing any percentage does not redistribute the load evenly over what remains.

Try this as a simple exmple - looking at a building with three rows of columns.

A---------B---------C
1---------2----------1
So we have a number of columns in row A ditto row B and also row C The total load on each row would be something like the 1--2---1 I showed.

Pretend there are no end walls and end wall columns.

If we cut all the "C" row the load carried by "C" is not shared uniformly. The most likely result is:
A---------B---------C
0---------4----------0

now that is an extreme example but the principle is of major importance in understanding the cascade failure of the impact zone which actually occurred on 9/11 (Whether or not we consider there to have been some human assistance.) And every time you see a post saying something like "It cut 30% of the columns so there is a 30% load increase....." No way José!

I have probably raised some issues which need to be taken into account before any comments I may have on your final paragraphs so I will pause here.

SanderO wrote:...Now with heat beginning to work the remaining columns which are now at a much lower safety factor having taken on the axial loads of the destroyed columns from above... are growing weaker as their temps rise. Right away the FOS was well below 2 (perhaps 1.5 or so) with the plane strike affecting 4 of the 8 columns on the north side of the core (Tower 1). Now if these remaining columns lose 1/3 of their strength... they will buckle. it looks like 500° C might be enough temperature to buckle the north side of the core if columns 503, 504, 505, and 506 were destroyed on impact.

The next two columns 502 and 507 lose their strength from the increasing heat that leaves the two strong corner columns 501 and 508 holding up the entire north side of the OOS floors and all those above it. YIKES!

Is it possible to raise the temps of the remaining 4 columns to cause them to buckle? This looks like not as complex a take down as one would think.