The 9/11 Forum

Dr. G · by **Dr. G** on Wed Oct 14, 2009 5:57 pm

Heiwa:

First of all, your spring model won’t work because, as soon as the collapse of the Towers begins, the elastic limit of the structural steel is exceeded almost immediately. The elastic strain energy capacity of A36 steel is only about 20 J/kg compared to 36 J/kg for the energy released by the descent of an upper portion of a Tower through one floor height. If you take a total core column area at the 95th floor as 2 m^2 and the yield stress of the core column steel as 250 MPa you can calculate the time required for the elastic limit to be reached – it come out to less than 10 milliseconds. At that point you can say goodbye to your springs and say hello to plastic hinges.

Actually I think the perimeter columns were the Achilles’ heel of the Towers and the bolted column end-plate connectors were the weakest link in the structural integrity chain. If you look at the load-displacement curve for A325 bolts (See NIST NCSTAR 1-3D) you will find that these bolts fail after an elongation of only 0.3 inches, which requires an energy input of about 2000 J per bolt. This means that all the perimeter column bolts could be destroyed with an energy expenditure of a mere 2 MJ. This is theoretically possible if the deformation energy is directed to a small fracture zone within each bolt, however, in practice energy is dissipated not just within a bolt but also within the end plate and in the column itself. Nevertheless, it looks like all the perimeter column bolts could be fractured with an energy input of less than 50 MJ.

Appendix B of the FEMA Report on WTC 1 & 2 notes that as the perimeter columns lost lateral support they deformed out-of-plane from overloading eccentricities. It was estimated that as the eccentricity increased, the applied bending moment exceeded the bolt moment capacity when the eccentricity was about 4.5 inches, which would occur when a column was only about 2 deg off vertical.

A325 bolts were probably also the weakest link in the core columns, especially for the upper floors. The splice connections consisted of two splice plates connected to the columns by eight or twelve A325 bolts with an ultimate shear capacity of about 220 MPa. The splice plates were consistently stronger than the bolts so the columns mostly failed in tension through shearing of the bolts. This explains why very few buckled columns were found in the WTC rubble piles.

Major_Tom · by **Major_Tom** on Wed Oct 14, 2009 11:23 pm

Actually I think the perimeter columns were the Achilles’ heel of the Towers and the bolted column end-plate connectors were the weakest link in the structural integrity chain. If you look at the load-displacement curve for A325 bolts (See NIST NCSTAR 1-3D) you will find that these bolts fail after an elongation of only 0.3 inches, which requires an energy input of about 2000 J per bolt. This means that all the perimeter column bolts could be destroyed with an energy expenditure of a mere 2 MJ. This is theoretically possible if the deformation energy is directed to a small fracture zone within each bolt, however, in practice energy is dissipated not just within a bolt but also within the end plate and in the column itself. Nevertheless, it looks like all the perimeter column bolts could be fractured with an energy input of less than 50 MJ.

I agree. But there are 2 ways to interpret what you are saying.

They are the Achilles heel of the perimeter, no doubt. Directed devices can direct this energy to a small fracture zone and the bolts will break.

You can also just unbolt them. You just have to remember to turn the socket counter-clockwise.

Either way you look at it, they are the place to look.

A325 bolts were probably also the weakest link in the core columns, especially for the upper floors.

Only for the upper floors, no? Thanks for pointing this out.

In the draft version NCSTAR1-1A at

http://wtc.nist.gov/pubs/NISTNCSTAR1-1A.pdf

there are original notes from designers about specific aspects of construction.

They inspected selected bolt and weld connections from time to time in the towers and they record these inspections in this report. Great info, because they explain how they access the connections to inspect them. It's like a how-to manual for connection access.

They describe how the core columns around the 90th floors are bolt connections. They tell you how to access them through the elevator shafts and what you have to do to get to the cornermost column connections of 501, 508, 1001 and 1008 on the very floors where the airplane hit.

The four corner columns, which we would associate with being the strongest, were bolted according to the inspection reports.

From these reports we can see that both core and perimeter connections in the region of the airplane strikes were bolted, not welded or rivetted.

We cannot see inside the core in the video clips but we can see the perimeter. What you say is interesting, Dr G (as your posts tend to be). As you may know, I have been pointing out unbuckled columns falling from the collapse zones, most all of which are broken at bolt connections, for some time. You are suggesting they broke naturally while I suggest otherwise. We can actually look closely at collapse initiation at the 8 faces to see which one of us may be right.

Great topic. Maybe the wrong thread?

David B. Benson · by **David B. Benson** on Wed Oct 14, 2009 11:28 pm

Dr. G wrote:Actually I think the perimeter columns were the Achilles’ heel of the Towers and the bolted column end-plate connectors were the weakest link in the structural integrity chain. If you look at the load-displacement curve for A325 bolts (See NIST NCSTAR 1-3D) you will find that these bolts fail after an elongation of only 0.3 inches, which requires an energy input of about 2000 J per bolt. This means that all the perimeter column bolts could be destroyed with an energy expenditure of a mere 2 MJ. This is theoretically possible if the deformation energy is directed to a small fracture zone within each bolt, however, in practice energy is dissipated not just within a bolt but also within the end plate and in the column itself. Nevertheless, it looks like all the perimeter column bolts could be fractured with an energy input of less than 50 MJ.

I don't quite follow this, but first off, didn't you mean NCSTAR1--2D? (I suppose might be 3D also...)
My problem is all the perimeter column bolts. All on one story? Incidently, 50 MJ also is about the energy required to destory all the truss seats, both internal and and external, on one story.

The splice connections consisted of two splice plates connected to the columns by eight or twelve A325 bolts with an ultimate shear capacity of about 220 MPa.

How high up did this arrangement start? I'm fairly sure that the wide flange rolled steel columns (H-columns) were fillet welded together for several floors above the end of the box columns and I had thought this continued up to at least around floor 100.

Dr. G · by **Dr. G** on Thu Oct 15, 2009 1:00 am

DBB:

The load-displacement curves for A325 bolts that I referred to are on page 31 of NIST NCSTAR 1-3D. As for your other question, see M_T's post.

Major_Tom:

Well that's very interesting information about where only bolted columns were used. However, from what I've seen, welded splices were not orders of magnitude stronger than the bolted ones - perhaps twice as strong - so we still have only 100 MJ to fail the perimeter columns on one floor. What is interesting is that this energy would be more or less constant all the way down the towers giving an approximately constant collapse resistance "force", as observed.

By the way, its instructive to compare these energies to those reported by Wierzbicki for the aircraft impacts. He estimates the energy to break (i.e. slice through!) about 50 perimeter columns was about 100 MJ. This would be similar to the plastic buckling energy of 50 columns. Clearly the energy to simply break the bolt connections was a lot less than this.

David B. Benson · by **David B. Benson** on Thu Oct 15, 2009 1:18 am

Dr. G --- Thanks, but I still don't understand the 50 MJ estimate. Is that the per floor energy to break the bolts?

Heiwa · by **Heiwa** on Thu Oct 15, 2009 4:49 am

Dr. G wrote:Heiwa:

First of all, your spring model won’t work because, as soon as the collapse of the Towers begins, the elastic limit of the structural steel is exceeded almost immediately. The elastic strain energy capacity of A36 steel is only about 20 J/kg compared to 36 J/kg for the energy released by the descent of an upper portion of a Tower through one floor height. If you take a total core column area at the 95th floor as 2 m^2 and the yield stress of the core column steel as 250 MPa you can calculate the time required for the elastic limit to be reached – it come out to less than 10 milliseconds. At that point you can say goodbye to your springs and say hello to plastic hinges.

OK G, the upper part C with a footprint of 4000 m² weighing say 33 000 000 kgs produces 36 J/kg of energy (total 1.19 GJ) when dropped 3.7 meters, but how does part C apply this energy on 2 m² of core columns of lower part A? The core structure is only 0.05% of the total footprint.
I would estimate that most energy released by C simply misses the core structure. Or do you still work in 1-D? Then the cross area of the foot print is 0 m²!
Regardless, the energy applied at contact C/A is also applied to upper part C. What happens to upper part C at impact?

T_Szamboti · by **T_Szamboti** on Thu Oct 15, 2009 5:50 am

Dr. G wrote:Heiwa:

First of all, your spring model won’t work because, as soon as the collapse of the Towers begins, the elastic limit of the structural steel is exceeded almost immediately. The elastic strain energy capacity of A36 steel is only about 20 J/kg compared to 36 J/kg for the energy released by the descent of an upper portion of a Tower through one floor height. If you take a total core column area at the 95th floor as 2 m^2 and the yield stress of the core column steel as 250 MPa you can calculate the time required for the elastic limit to be reached – it come out to less than 10 milliseconds. At that point you can say goodbye to your springs and say hello to plastic hinges.

Actually I think the perimeter columns were the Achilles’ heel of the Towers and the bolted column end-plate connectors were the weakest link in the structural integrity chain. If you look at the load-displacement curve for A325 bolts (See NIST NCSTAR 1-3D) you will find that these bolts fail after an elongation of only 0.3 inches, which requires an energy input of about 2000 J per bolt. This means that all the perimeter column bolts could be destroyed with an energy expenditure of a mere 2 MJ. This is theoretically possible if the deformation energy is directed to a small fracture zone within each bolt, however, in practice energy is dissipated not just within a bolt but also within the end plate and in the column itself. Nevertheless, it looks like all the perimeter column bolts could be fractured with an energy input of less than 50 MJ.

Appendix B of the FEMA Report on WTC 1 & 2 notes that as the perimeter columns lost lateral support they deformed out-of-plane from overloading eccentricities. It was estimated that as the eccentricity increased, the applied bending moment exceeded the bolt moment capacity when the eccentricity was about 4.5 inches, which would occur when a column was only about 2 deg off vertical.

A325 bolts were probably also the weakest link in the core columns, especially for the upper floors. The splice connections consisted of two splice plates connected to the columns by eight or twelve A325 bolts with an ultimate shear capacity of about 220 MPa. The splice plates were consistently stronger than the bolts so the columns mostly failed in tension through shearing of the bolts. This explains why very few buckled columns were found in the WTC rubble piles.

Do you still believe all of this could happen without any deceleration and the fact that the upper block in WTC 1 was pretty much disassembled into rubble before it went through ten stories of the lower block? Or that WTC 7 was anything other than a controlled demolition with pre-positioned cutter charges?

Heiwa · by **Heiwa** on Thu Oct 15, 2009 3:20 pm

Dr. G wrote:Heiwa:

First of all, your spring model won’t work because, as soon as the collapse of the Towers begins, the elastic limit of the structural steel is exceeded almost immediately. The elastic strain energy capacity of A36 steel is only about 20 J/kg compared to 36 J/kg for the energy released by the descent of an upper portion of a Tower through one floor height. If you take a total core column area at the 95th floor as 2 m^2 and the yield stress of the core column steel as 250 MPa you can calculate the time required for the elastic limit to be reached – it come out to less than 10 milliseconds. At that point you can say goodbye to your springs and say hello to plastic hinges.

So the steel of the lower part A can only absorb 20 J/kg before getting plastic and I assume that the steel in upper part C can also absorb same amount. BTW - how did you calculate the 20 J/kg? What steel are you talking about?

However, using your strange particulars, it seems that parts A and C together can absorb 40 J/kg energy elastically (before plastic deformation starts) at impact (as there are two parts in the collision splitting the energy/forces 50/50) and that only 36 J/kg is applied which means that the impact is arrested immediately - less than 10 milliseconds? - and that C just bounces on A. This I have concluded a long time ago. But in my approach the energy is applied to different parts in different ways, e.g. columns punching holes in floors, broken elements displacing and rubbing against each other causing friction to assist in the arrest, etc, etc. I have never heard about the strength of an element being described in J/kg!

Right? Or did I miss something?

Re plastic hinges developing in structures, I have seen plenty of those ... and the structure didn't collapse! Reason is that the geometry of the structure evidently changes when plastic hinges develop and ... the load slips off. Happened to me some years ago. I was stopping at a traffic light and there was a BIG BANG! The car behind me didn't stop, you see, and tried to one way crush me. Luckily the bumper of my car deformed plastically and deflected the intruding load.

Dr. G · by **Dr. G** on Thu Oct 15, 2009 4:22 pm

The energies I have estimated are to break all the perimeter column splice bolts on one floor. All A325 bolts are assumed to be 36 ksi steel.

Now we know the perimeter columns in whole horizontal sections of the impact zones of both towers bowed significantly in the moments before the total collapses. I fail to see how cutter charges made columns bow like that. If any posters believe otherwise I would like them to explain how these charges worked! As for thermite on the perimiter columns, it would have been clearly visible in the large areas where the columns bowed, but was not seen; so we can rule out thermite, super or nano, as well. (As I have said before, proponents of CD theories never offer anything but hand-waving fantasies about how the alleged dirty deed was done, .... and yet they are so quick to offer criticism of "natural collapse" theories!)

I suspect that once the bowing exceeded a critical amount and the ultimate moment capacities of the bolted connections were exceeded you would have a chain of catastrophic perimeter column failures running along one floor level. Because this "un-zipping" moved at a finite speed around the perimeter wall, a tipping/dropping motion of the upper block was initiated. This would cause entire floor assembies and the associated office live-loads to impact violently on the floors below. Lateral support for the perimeter columns on the floor below the collapsing floor would then be rapidly lost initiating a second floor collapse and so on all the way down the towers. Thus we do not have (or need) axial column-to-colum impacts and, (sorry Heiwa), no bouncing columns and collapse arrest either....

Heiwa · by **Heiwa** on Thu Oct 15, 2009 6:07 pm

Dr. G wrote: This would cause entire floor assembies and the associated office live-loads to impact violently on the floors below. Lateral support for the perimeter columns on the floor below the collapsing floor would then be rapidly lost initiating a second floor collapse and so on all the way down the towers. Thus we do not have (or need) axial column-to-colum impacts and, (sorry Heiwa), no bouncing columns and collapse arrest either....

Sorry G, I do not follow; wouldn't the entire floor below (of part A) also violently impact the floor above (of part C) initiating a collapse of the floors above, producing rubble, all the way up the tower + mast? The top part is much weaker than the bottom, solid one, part connected to ground. I have great difficulties seeing how a weak, light, mostly, 95%, air, structural assembly C can do much harm to something stronger, part A, that carried the weak part, C, statically without problems (in a gravity field on earth).
Do you suggest dropping an egg in a pan produces a hole in the pan?

Major_Tom · by **Major_Tom** on Thu Oct 15, 2009 6:19 pm

Dr G, there are many features, like inward bowing, that have been discussed in other threads.

Not hard to do.

We have talked about your idea of unzipping and it's virtual nonexistence for WTC1.

Every one of your conplaints have been addressed elsewhere and your post shows me you haven't been paying attention to certain threads which focussed only on the perimeter

I think you are looking in the right place: Perimeter action during collapse initiation.

But it is probably best to really look at your unzipping action, particularly along the west and north face of WTC1 and east face of WTC2.

Lucky for you we have collected pretty good video and images in other threads of the very process you describe .

Since all that effort was taken to collect them, the least others can do is look at them.

Please show me your unzipping along the WTC1 w and n faces and along the WTC2 east face. It is quite interesting.

(As I have said before, proponents of CD theories never offer anything but hand-waving fantasies about how the alleged dirty deed was done, .... and yet they are so quick to offer criticism of "natural collapse" theories!)

Strange thing to say considering the fate of WTC7. Never understood your ability to suspect demo like the rest of us for WTC7 while thinking that Al Qaida took care of the other two buildings by themselves. All on the same day.

Much good work has been done that I suspect you have not yet read. Your post is a great way tolead into a discussion of WTC1 and 2 perimeter behavior around the collapse initiation regions and into the upper blocks. But there are already developed threads for that which you probably have not read.

peterene1 · by **peterene1** on Thu Oct 15, 2009 8:13 pm

Now we know the perimeter columns in whole horizontal sections of the impact zones of both towers bowed significantly in the moments before the total collapses. I fail to see how cutter charges made columns bow like that. If any posters believe otherwise I would like them to explain how these charges worked! As for thermite on the perimiter columns, it would have been clearly visible in the large areas where the columns bowed, but was not seen; so we can rule out thermite, super or nano, as well. (As I have said before, proponents of CD theories never offer anything but hand-waving fantasies about how the alleged dirty deed was done, .... and yet they are so quick to offer criticism of "natural collapse" theories!)

Hahahahahhhahhaahahhahahah!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

It's official! :lol:

Busted!

I've been waiting for this moment for so long! :lol:

Well, let's look at the "out of service" elevator shafts on 9/11!

http://www.youtube.com/watch?v=WPtAOtO1nTY

there's like gazzilion of pages on this forum, dealing with the bowing only

OneWhiteEye · by **OneWhiteEye** on Thu Oct 15, 2009 8:17 pm

Heiwa wrote:Do you suggest dropping an egg in a pan produces a hole in the pan?

Joke, right?

peterene1 wrote:Hahahahahhhahhaahahhahahah!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

It's official! Busted!

? Please elaborate.

peterene1 · by **peterene1** on Thu Oct 15, 2009 8:20 pm

He admited that the either did not read a very great percentage of this forum or that he has some kind of selective amnesia.
The bowing has been discussed to death.

OneWhiteEye · by **OneWhiteEye** on Thu Oct 15, 2009 8:23 pm

Ok, I see. But have you read every post in the forum? I think I might have, actually. If not, does that cause you to withhold comments on subjects of interest to you? Maybe somebody has said things about a subject, maybe even Dr G, and you haven't read them, either. Not an accusation; you tell me.

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