WHERE DID THE TOWERS GO? by Dr. Judy Wood, Ph.D

[Jeffrey Orling]

Jason,

Thank you for being open minded about this matter. Steel framed have the beams / girders actually which carrry the floor loads connected to the SIDE of the columns in almost all cases. The reason why is simple. Let me illustrate with an example.

Let's look at the a point lot down in the structure. The floor load is relatively small, even if it is for an large portion of a floor and is carried by a single girder which needs to be affixed to a column which transfers the load to the foundation. That column is carrying the load of all the columns above it... and their portion of the floor loads attached to them And this is why the column cross section is progressively larger moving down the structure. If you placed the a girder on top of a column, then you would have to place the next column on top of the girder and so one. The girder then, is having the entire load above placed on its end... the portion of the girder which is on top of the column. If you examine the cross sectional area of the girder... the web... will see how small it is compared to the column above and below it. The web would be crushed ... too small to support the load.

We often weld in web stiffeners to assist a H shaped beam to support the loads when there are concentrated vertical loads placed on it mid span. A steel beam works by placing the compression and tension material as far apart and using a relatively thin tall web to separate them. A wood or concrete beam has a uniform cross section typically which is why you CAN rest a solid wood beam directly on a solid wood column (with the same compressive yield strength.

So there is no other way to erect a multi story steel frame than to attached the loads (girders) to the sides of the columns.

There were several contributing factors which assisted the gravity driven collapse phase.

1. the floor system was column free... this made the floors long span and placed all the columns to support them at the outside edge of the building and at the perimeter of the core. This required that all the floor loads be directed by the beams... there were no girders... to the few columns that would carry the floor loads. At the facade the floor beams truss joists were attached to every other column at the facade. The other columns received the axial loads via the spandrel plates which connected all the facade columns together. On the core side the floor trusses were connected to a channel section at 80" oc (truss spacing) which was then connected to the perimeter core columns... 8 of them on one side and 6 on the other with the corner core columns carrying loads from bother sides. The core side had several possible failure points... the truss seats themselves, the channel which supported them... the beam stub outlookers.. which were very short beams connecting the channels to the columns and the bolts and welds of all the connections. As you progress from the floor to the column the yield strength of the component must increase as it carries the aggregate load of what ever is connected to it.

2. To make the floor structure long span... it had to be deep. The deeper a beam is the less it deflects per given load.. hence longer spans have deeper beams. Deeper beams make the entire structure taller... and would make the floor system very heavy as well. Heavy means more steel, more expense, and larger columns and also more expense... and connection and erection issues. The floor system was an off site pre assembled approach.

To make the floor system lighter and thin enough a truss system was used. A steel truss is like H beam in that it has a compression chord at top and a tension chord on the bottom which "do the work" separated by diagonals... in the case of the towers' floor trusses - 1" Ø bars. This allowed for wire pipes and ducts... "building "service" to run perpendicular to the trusses without cutting holes in them which is also expensive and weakens a beam or girder and must be done in its center and of a limited size as well, else the beam action is lost.

The trusses are light, very light, and the floor which they supported was made as light as possible too - no stone aggregate concrete. Concrete needs a form to pour it on. The floor system instead used light weight 22 ga (the lightest used for this) corrugated metal decking to support the concrete pour. The decking ran parallel to the trusses for economy reasons and to allow conduits for wiring to be run in the concrete. This was the weaker direction to orient the decking. Additional cross trusses were inserted perpendicular to the main pre assembled trusses which tied the entire system together... giving the entire floor a membrane action. Everything working together us a composite. A composite floor is made stronger by composite action and so the individual components of a composite can be made weaker and lighter and cheaper as long as the composite performs to spec.

And so it is why the WTC twin tower floors (components) were so (relatively) light... and therefore inexpensive and easy to erect. And as we saw easy to come apart when off spec loading occurred. And not only that... To reduce the weight and the cost the PANYNJ requested and were granted a design load reduction for the long span open office floor. NYC code calls for 100 pounds per square foot and the PANYNJ were allowed to use a design of 58#/SF.. a 42% reduction. Their claim was that normal conditions in offices rarely see loads of 100#/SF. The request was granted. The tower floors were designed to be 42% weaker than all other office floors in NYC.

3. By relocating the columns out of the main floor space the entire floor area was more vulnerable to failure not just an area within one - 4 column bay as we see in all other steel frame designs. This column free floor space design was touted as more flexible for designers of the fit out of the tenant floors, AND more economical to build... and quick too.

It must be emphasized that the was no expectation that ANY floor would see sufficient imposed loads to fail it. Tenants are not allowed to exceed the load allowances... even in elevators. If these loading limits are observed there is no reason to expect any structural failure.

As explained in many of my posts, the collapse was inevitable ONCE the threshold load was exceeded... a load which PANYNJ had authorized be reduced 58#/PSF which made this failure point lower. But the designers never expected that a single floor could support 4, 5, 10 or 14 floor weights and their contents. If this load was imposed on ANY floor in that building... or ANY BUILDING for that matter is would fail and collapse.

And that is precisely what happened in Phase II... Phase I delivered the over design imposed load onto the floor system in the undamaged section of the tower... first to the top most floor... 96 or so... and then the runaway collapse (ROOSD) ensued. As stated we don't know how those 14 top floors were "destroyed" and converted into the imposed load for floor 95. It doesn't seem likely that office fires could leading to such a destruction. But the destruction of those floors could be a "mini" (not so mini actually) destruction up top 14 floors engineered with explosives and or cutter charges to the relatively small steel sections above floor 96. If the objective was to "free" the mass to crush the floors progressively... then calculations involved the creating the minimum threshold mass to initiate the ROOSED... and that may be as few as 4 or 5 floors!

The much more difficult concept to grasp is the fate of the core columns and this was made more difficult because we can see what happened to most of them except at the end after the floors had collapsed and the facade peeled away.

A steel frame is able to stand erect because it is braced by beams affixed to the sides of columns. Without and floors a steel frame is a 3 dimension lattice. A frame can be made rigid with very stiff joints or use of diagonal bracing... or as in wood studs application of a membrane - wall sheathing - to the studs. Diagonals are very "inconvenient" for any number of reasons in tall structures... but they are often used to stiffen the entire structure to resist wind loads which are enormous and act laterally not axially on the columns

The towers relied and rigid non rotating connections of the beams/bracing to the columns called moment connections. The bracing beams had their webs welded and bolted with angles to the columns. The welds and bolts carried the full load of the connections.

Perhaps the most difficult concept to understand and rarely encountered is "self buckling" of a column. Euler, a physicist, discovered that a column's strength... the axial load it can support is not ONLY determined by its cross sectional area and type of material... different materials have different compressive strengths... but by its unsupported length.

He described three classes of columns - short - medium and long and this were expressed in ratios of the length to their cross sectional area. Short columns are the strongest... long are the "weakest" for a given cross sectional area.

But there is a upper limit for long columns. Long columns made of steel cannot be longer than 150 times their shortest cross sectional dimension. So a column which is 12x24 inches in plan can not not longer than 150x12" or 150 feet tall. If one attempts to erect a column of these proportions it will buckle at a point below its mid height. It will fail from its own weight. It will "self buckle". This is "Euler Buckling".

Columns, are made as small as possible in cross sectional area to "do the job" and this makes them cheaper, uses less real estate and so forth... but they have to have sufficient area for floor beam connections to be made as well.

In the case of steel high rise frames the bracing is at each floor level and so the columns are considered short and therefore quite strong. The core column 501 which had a short axis dimension of 22" and a floor height of 144". The slenderness ratio was about 1/7. The actual column length was 36'. But the effective length was 12'

However in a high rise one column is placed on top of the next and so core column 501 was 1362 feet high made up of 38 columns... most 36' long and a few at 42 feet... with bracing at each 12'. So again each segment was a short column. Even at the top where the cross section has been reduced to a 12" wide flange the slenderness ratio was 12 and this still made it a short column and not subject to self buckling.

When the floors collapsed, they destroyed the beams and girders which carried them. Those beams and girders were overwhelmed by the same excessive (to their design spec) imposed loads. It's likely that their connections failed rather than the beams bending and deflecting or shearing. They would shear if the connections were stronger than the beam itself. And this DID occur in some cases.

As the floors collapsed past the columns... leaving them without their lateral bracing... the effective unbraced length grew. After the collapse of 16 floors... say from 96 to 76 for example... the unbraced length of the 20 floor tall unbraced column was 192 feet and the short axis was about 18" 1/160 which EXCEEDED the slenderness ratio limit for a tall column which is 150. Therefore this 20 floor high unbraced section of column HAD to buckle from "Euler buckling". This of course was made even easier because it was already created from 36' long sections and the welds at the column joints failed and the sections were sprung out of column beginning at below half its unsupported height. Having collapsing material assault it laterally only added to its inherent instability.

The only columns which survived at all were the largest in cross section. And they only survived as long as they did because the bracing was still attached to the next column. This can be seen in the spire columns of rows 500 and 600. The bracing made these pairs effectively a column of about 15' by 22" in plan view... but this didn't help much and even those massive core columns buckled and failed... springing off their 36' long sections below mid height. CC501 weighed almost 1100 tons up to the 78 floor and when it buckled perhaps as much as 400 tons above its mid height accelerated straight down at free fall... with nothing to support, resist or stop it.

The columns had very little strength relatively in the lateral direction... without the bracing. Even without Euler buckling coming into play... there was enormous lateral loads coming from the collapsing debris of the 90+ floors above as the facade acted like a chute containing it. But this was a futile effort by the facade and the collapse rubble exerted a lateral force which pushed the facade over and acted in a similar manner on the core columns. So the floors did not ONLY collapse passing the columns, stripping off the lateral bracing... but it also exerted lateral forces ON the columns (absent the lateral bracing) which contributed to their fracturing apart at those same weak points... the welds applied to the outer perimeter which connected them. Understand that if CC col 501 for example, a floor 18 had a cross sectional area of 5.08 feet, the weld connecting it to the column above it was only about 150" in length an it's cross section was at most a foot or two in area. This is why the columns were found (seen in the debris) in "neat" sections broken at their welds.

It's likely that the lateral pressure from the debris was a factor as well as the Euler buckling. The latter was the mechanism for the "spire" columns which survived the floor collapse and were stronger and less likely to yield to the lateral forces. The debris might have actually braced the bottom of the spire columns... but the Euler buckling ruled and they self buckled and sprung or toppled.

[Kyle Burnett]

There is no violation of any laws of thermodynamics in the phase II of the collapse.

Again, while there inherently can't be any violation of the laws of physics in what physically happened, ill-conceived explanations for what happened can violate the laws of physics, Bazant's nonsense being one notable example. Are you incapable of comprehending that distinction?

And Kyle is correct is that I don't present a theory, but an explanation based in basic engineering concepts supported by the observations.

I'd never suggest any explanation is "supported by the observations," as such a notion flies the the face of the scientific method. In science, observation is used to develop a hypothesis, while support for the proposed explanation comes through experimental confirmation.

I am not even sure why Kyle's objection is at this point to the engineering concepts which describe a gravity driven destruction from the plane strike zone down driven by the mass of the floors above the strike.

Again, I contend that what you proclaim happened to the towers could not result in such rapid and complete destruction of a building, but rather something more along the lines of what can be seen in these simulations at best. Sure, if broken free the mass above can shred through the floors below, displacing columns along the way, but all that steel and concrete breaking apart and and pushing each-other around results in all sorts of angular momentum and friction which limits the amount of energy left to crush the remaining structure bellow, and which your notions of floors turning into a Landkreuzer tank and shredding through the building simply don't take into account.

[Jeffrey Orling]

Kyle,

The interactions between the elements, chunks, debris, particles of the avalanche do not negate the gravity energy which remains operative on all the mass. The mass would have to be destroyed to free itself from the force of gravity. The mass of the towers was "transformed", dissociated but still has the destructive potential energy of gravity turned into KE which it was no longer locked inside the matrix of the structure which transferred the loads (gravity PE) to the foundation through the columns.

Engineering is derived from empirical tests/experiments. No need to test what a 10wf31 can support spanning 30'... or what load will cause it to deflect or buckle its web. It's already been established.

While you might be able to model some aspects of the failure, you can't scale such a model and get reliable results. But your call for a repeatable experiments is a straw man argument. Engineering / structural design and forensic analysis of structural failure is pretty much settled science. Forensic reports are made all the time without modeling to prove the analysis.

Was it you who played with models trying to simulate the collapse?

[Kyle Burnett]

The interactions between the elements, chunks, debris, particles of the avalanche do not negate the gravity energy which remains operative on all the mass.

Sure, the intact structure below is what negates the gravity energy of the mass above it, which is why building generally remain standing. However, despite your notions of floors turning into Landkreuzer tanks as they break free, in reality such a process results in a tangled mess of columns and beams and everything else pushing on each other, and hence limits how quickly and completely such an "avalanche" can destroy a building, as seen in the simulations I've linked previously.

But your call for a repeatable experiments is a straw man argument.

No, a straw man argument is when one ignores another's argument and constructs a misrepresentation of it to refute instead. My call for for experiments is an appeal to the scientific method, a methodology which would have kept Bazant's nonsense out of the Journal of Engerneering Mechanics had it been respected, and which I'm quite sure your notions of what happened to the towers could never pass the test of either.

Was it you who played with models trying to simulate the collapse?

No, that was psikeyhackr. Were I to invest the effort into constructing a model of how the towers came down, either a scaled down physical model or a full scale computer simulation; it would be rigged with explosives all the way down, as I've no doubt that's what it took took for them to come down as quickly and completely as they did.

[Jeffrey Orling]

In fact, the design of the twin towers would not result in a tangled mass being arrested and supported by the columns. WRONG!

The twin towers design off the long span column free interiors were what enabled the floors being swept away and destroyed by the destructive mass descending on them.

I am not asserting the floors turn into tanks.. but the mass of broken floors and contents had the destructive mass of a tank and more.

In order for columns to support loads the loads must be applied to the columns in a manner that the column can support the load and the connect to it is strong enough. The loads were attached to the columns in the core via beam stubs which were designed to transfer a specific load with appropriate safety factor. If a core column descended on a beam stub it would destroy it and the beam stub would NOT be able to transfer the weight of the descending column to the column to which it was affixed. Sure if a refrigerator dropped onto the beam stub it would be mangled and come to rest and that beam stub would not fail and the refrigerator load WOULD be transferred to the column it was attached to. But in the collapse of the debris.. the beam stubs, truss seats, bracing was over come by the dynamic loads and RIPPED off or fractured and were severed from and unable to transfer loads to columns and the columns were therefore UNABLE to arrest the descent of the huge loads of collapsing floor rubble.

Sorry Charlie, you can't describe how to get those loads onto those strong columns in such a scenario. You are dreaming!

[Jeffrey Orling]

Kyle,

This is my last over with you about the scientific method and conducting experiments to prove established engineering principles. It is not necessary. Tests have been done... performance data established and used every day to design structures which stand.

You need to study the structure and some statics before making such "demands" on engineers to "validate" the principles which they use every day.

[Kyle Burnett]

In fact, the design of the twin towers would not result in a tangled mass being arrested and supported by the columns. WRONG!

Well, you just provided a textbook example of a straw man argument. I didn't say top down gravitational collapses of the towers would necessarily "result in a tangled mass being arrested and supported by the columns" but rather only noted that it "limits how quickly and completely such an "avalanche" can destroy a building." In other words, even if the descending mass is such that shreds the building all the way down, with only gravity acting on that mass shredding through all that structure takes time, and the rubble will wind up pulled high within it's footprint like the simulations I've shown. On the other hand, quickly winding up in a vast rubble pile largely outside the footprint of the building takes a lot of force latterly displacing all that structure for gravity to bring it down so quickly and over such a large area, hence the reason I've no doubt that explosives were used all the way down.

You need to study the structure and some statics before making such "demands" on engineers to "validate" the principles which they use every day.

Hah! What exactly are you calling demands here, while telling me what you suppose I "need" to do? It seems to me that you could stand to get a grip. That's a suggestion, not a demand.

[Jeffrey Orling]

Your argument is that the crushed debris is spread too far outside the footprint for gravity to be the force placing it there?

Most of the material outside the footprint was the steel which feel intact away from the collapse and the lateral impulse to get it there did not require explosives. I don't know how you established the distribution of the crushed material which was outside the footprint and so far from it that only explosives could account for how it got there. That sounds like a bit of speculation and observations which are not recorded officially. Gage likes to speak of dust 4-12 inches thick for miles around lower Manhattan but that is rubbish. There was no measurable thickness of dust at all on Canal Street. Fetzer claimed in another Judy Wood thread that the volume of dust was 20,000,000 cubic feet or some absurd number. All the floors slabs neatly stacked would barely reach 3 stories tall. The towers were 96+% air by volume as are most office buildings. There's not much there there. Judy Wood claims a collapse tower debris should be 30% of the building height... Another idiotic remark based on nothing scientific. Cole and AE911T insist that the spire was undermined by explosives which apparently went off 20 seconds or more after the rest of the explosives which "pulverized the 90,000 tons of concrete on mid air"... and I suppose they were placed on the 3rd floor so that the core columns would still be standing and sticking through the rubble pile... and exploded off the column weight 1100 tons leaving no blast deformation to the remaining column standing in the debris.

These are not observations of what happened or what remained, but made up rubbish which supports their pet theory of the engineered destruction of the towers top to bottom with explosives or directed energy weapons.

With all the core columns in each tower... almost 1,600 thirty six and almost 200 forty two foot long columns where is the signs of explosions at their ends?

I have stated that there could have been and likely WAS some nefarious cause to the initiation in Phase I which could have involved the pre placement of explosives and or cutter charges at the top... and this could account for the rolled sections found with eutectic burning of the steel and correlate with some thermitic residue found which Haritt told me was of the magnitude of 4 tons. And I don't think 4 tons of thermite could be spread throughout those three towers and explode them to bits as we've seen. Perhaps you have a calculation of the energy required to explode the towers to account for the observations and correlate that to the 4 tons and where it was placed? Of if more thermite was required... where was the other residue from explosives? Didn't Jones and Haritt not look for that? Wouldn't they announce it if they found it? I don't even think nano thermite can explode in a manner to produce the destruction claimed... I haven't seen experiments to demonstrate this. Sure if it was in the dust it needs to be explained how it got there.

How much explosive residue is found in an off the shelf CD for a Vegas high rise? Where are the studies of how much should be then found at the WTC site? I suggest that you head out with your collection apparatus to the next commercial CD of a steel framed tower and being collecting dust and data... and report back.

Demands or suggestions... you understood perfectly well. I suggest you provide the mechanism for the explosive destruction of the twin towers so that theory can be tested and compared to the debris found at the WTC. Be my guest.

[Kyle Burnett]

With all the core columns in each tower... almost 1,600 thirty six and almost 200 forty two foot long columns where is the signs of explosions at their ends?

The vast majority of the steel was shipped off to China for recycling without ever being properly cataloged. Are you ignorant of this fact, or are you being disingenuous in arguing as if it wasn't the case? Either way, I see no point in discussing this matter with you any further.

[Ed Jewett]

Who was responsible for the proper collection and protection of evidence? What processes or procedures were used or in place (or should have been)? Given the highly unusual nature of the event, what was the actual process involved in moving the steel?