Hardfire: Physics of 9/11

[psikeyhackr]

psik,

I'm not quite sure what to say, but I'll try.

In engineering, seemingly "complicated" words aren't so much created as they are agreed upon in the engineering community. Common engineering terms allow folks like poster Architect or NewtonsBit, to design something in their country, and have it built by architects/engineers in another county.

The language is not based on pretense whatsoever. It's based on having a common understanding among professionals in a particular speciality.

I'm sorry that having to learn new things bores you.

.
It looks like there were a total of FIVE uses of moment frame(s) in the NCSTAR1 report and they were all in one document. Notice that the first paragraph on page 75 is nearly identical to the one on page 40. I have seen that a lot doing searches on the NCSTAR1 report. I wonder how many of the 10,000 pages could be eliminated if all of the duplication could be extracted.

NIST NCSTAR 1-1

Design, Construction, and Maintenance of Structural and Life Safety Systems

Page 40:

Above floor 7, the building had typical steel framing for high-rise construction. The floor systems had composite construction with steel beams of 50 ksi yield strength supporting concrete slabs on metal deck, with a floor thickness of 5.5 in. The core and perimeter columns supported the floor system and carried their loads to the foundation. Above floor 7, the perimeter moment frame resisted wind forces. Below floor 7, a combination of moment and braced frames around the perimeter and a series of braced frames in the core resisted the wind load.

Page 75:

Above floor 7, the building had typical steel framing for high-rise construction. The floor systems had composite construction with steel beams supporting concrete slabs on metal decks, with a floor thickness of 5.5 in. The core and perimeter columns supported the floor system and carried their loads to the foundation. The perimeter moment frame also resisted wind forces. Columns above floor 7 did not align with the foundation columns, so braced frames, transfer trusses, and transfer girders were used to transfer loads between these column systems, primarily between floors 5 and 7. Floors 5 and 7 were heavily reinforced concrete slabs on metal decks, with thicknesses of 14 in. and 8 in., respectively.

Page 75:

The substation’s lateral system consisted of a moment frame along the northern row of interior columns. Along the south edge of the substation there was a braced frame. This braced frame was coincident with the north side of the WTC 7 core. Lateral loads from WTC 7 were passed directly from the core above to the Con Edison braced frame below. There were also two moment frames within the substation, oriented in the north-south direction, one on each end of the WTC 7 core.

.
So how important is it with only 5 uses in 10,000 pages?

psik

 

[Newtons Bit]

Yeah, Newton, thanks.

I was thinking about the vertical shear between the floor slabs and the columns.

I'm familiar with the details of beam deflections. I designed electronic connectors & switches for years. And that's exactly how I think of the towers. Big ole boxy cantilever beams. Of course, my beams weren't as porous & discontinuous as this one.

We'd refer to the wind load as a distributed load, which results in a decreasing shear load as you move up from the ground.

Unfortunately, all of the really interesting stuff happens as it starts to starts to come apart. For the guys that did the analysis, it must have been like working on the shuttle disaster board. Fascinating and tragic.

Hard to imagine how frivolous some folks take it.

tom

Right. The TOTAL shear in the frame decreases as the height increases. However the incremental shear applied at each diaphragm increases as the height increases.

It's a subtle but important note as it shows that the strength of the columns required as the building goes up doesn't fall off by any sort of 1> exponential curve.

 

[ozeco41]

.....Unfortunately, all of the really interesting stuff happens as it starts to starts to come apart. For the guys that did the analysis, it must have been like working on the shuttle disaster board. Fascinating and tragic....

I call it the "What if?" engineering.

...and so often the what will really happen is only "predicted" in hindsight.

 

[Minadin]

If you think of it like a sideways cantilever attached to the ground, and the wind load acting like a weak version of gravity, wouldn't the shear (from wind) be consistent along its length, but the bending moment become greater nearer the base?

Perhaps I am confused.

 

[Newtons Bit]

If you think of it like a sideways cantilever attached to the ground, and the wind load acting like a weak version of gravity, wouldn't the shear (from wind) be consistent along its length, but the bending moment become greater nearer the base?

Perhaps I am confused.

Of course

 

[femr2]

(snip)When I refer to a column AT a floor, I'm actually referring to the column that is supporting that floor.(snip)

I guess that explains why the floor height increase for the mechanical floors begins one floor below the floors designated 'mechanical'.

 

[GlennB]

.
I can't tell if you are being sarcastic or if you actually buy that crap. I had to research "moment frame". I'll check if they ever used the term "moment frame" in the NCSTAR1 report when I get home tonight.

I figured that "moment" referred to "moment of inertia". People are always using that to make stuff seem complicated.

A final effort ... if people don't use technical terms such as "moment frame" then they're reduced to describing the structure or device every single time. In this case something like "wind-force resisting box-shaped steel frame". Which is so clumsy it's stupid.

Yesterday I used a mitre saw. You, however, would prefer me to say "I used that saw where you can clamp the wood and set the exact angle of the cut via a rotating guide"?

 

[Dave Rogers]

Energy loss in inelastic collisions

It's about time someone cleared up the question of inelastic collisions, conservation of momentum and energy loss to deformation, because it seems to be a common mistake that the two are somehow unrelated and separable. Gordon Ross made this error, and femr2, although having provided an optional correction to the WTC collapse simulator, appears not to appreciate that it is indeed an error. Here's a quick worked example to show that deformation energy in an inelastic collision and kinetic energy loss due to conservation of momentum are far from being unrelated; they are, in fact, simply two ways of looking at the same phenomenon. Note to moderators: This seems to me to be a reasonable thread in which to post it, but I have no objection to a move or split of anyone disagrees.

Beware: mathematics lies ahead.

Let's suppose we have a moving block (block 1) of mass M travelling at velocity Vi, striking a stationary block (block 2) of mass m. The two blocks deform perfectly plastically on impact, such that each is able to exert a force up to F on the other without deforming at all, but when the force reaches the value F both blocks crumple. (This isn't meant as a representation of the specific case of the floor-on-floor impacts in the Twin Towers, rather as a generalised model of an inelastic collision.) We can predict that there will be a deformation force F between the two blocks while the first is moving faster than the second, and that as soon as their velocities match the deformation will stop and both will continue to move at the same velocity. Friction will be assumed to be negligible.

We know from the conservation of momentum that the final velocity Vf will be:

(1) Vf = MVi/(M+m).

We can also calculate that the difference between initial and final kinetic energy is:

(2) Delta E = MVi^2/2 - (M+m)Vf^2/2

Substituting for Vf and rearranging, we get:

(3) Delta E = MmVi^2/(2(M+m)).

What happens, though, when we look at this from the point of view, not of energy and momentum, but of the forces on the two blocks? This must tell us about the deformation processes, because the deformation force is the only force present between the blocks.

I'll define t=0 as the time at which the moving block strikes the stationary block. The moving block will then experience a force -F, and its velocity will vary as:

(4) V1 = Vi-Ft/M

up to a time T when both blocks are moving at the same velocity. The stationary block will experience a force +F, and its velocity will vary as:

(5) V2 = Ft/m

until time T. At time T, V1=V2=Vf, so we can solve for T by substituting into (4) and (5),

(6) Vi-FT/M = FT/m

giving,

(7) T = MmVi/F(M+m)

This gives a final velocity:

(8) Vf = TF/m = MVi/(M+m)

which is the same as the conservation of momentum result in (1).

We can also determine the work done by block 1, and the work done on block 2. Block 1 moves through a distance X1 while exerting a force +F on block 2, and block 2 moves through a distance X2 while exerting a force -F on block 1. We can determine these distances to be:

(9) X1=ViT-FT^2/2M

(10) X2=FT^2/2m

The total work done in crushing is the work done by block 1 less the work done on block 2 by the crushing force, so:

(11) Work done = F(X1-X2)

Substituting in the values of X1 and X2, we find the work done in crushing is:

(12) Work done = MmVi^2/2(M+m).

This is the same as the difference between intial and final kinetic energy in (3).

OK, so we've worked out the velocities and energies two different ways, and got the same answer. Big deal, you may say; what does all this mean?

It means two things.

Firstly it means that, starting from the deformation behaviour of the two blocks and nothing else, we can calculate their final velocity and the energy of deformation, and that these are the same as we get from conservation of energy and momentum. Therefore, the loss of energy due to conservation of momentum is not just a possible source of deformation energy; it is the deformation energy. Considering the collision alone, we expect all this energy difference to go into crushing of concrete, deformation of steel, or other forms of damage to the structure. There's nowhere else for it to go.

Secondly, notice that I didn't specify the internal mechanism by which the deformation force is exerted, and notice also that the actual value of that force drops out of the final numbers. It doesn't really matter how one block exerts a deformation force on the other - crushing, crumpling, buckling or whatever - only that it does. In fact, even variations in the value of that force in the course of the collision can be shown not to affect the final result (although that would take too much time and too much space on the forum; I'll leave it as an exercise to anyone who doesn't believe it). For example, a frictional force between the two blocks would have exactly the same effect. This means that Heiwa's repeated assertion that entanglement and friction will arrest the collapse is a red herring. That entanglement and friction still factors into the conservation of momentum calculation, and is still a force that has to be transmitted to the lower structure. If that lower structure can't stop the fall of the upper block, invoking entanglement and friction won't help.

To summarise: Simple Newtonian dynamics demonstrates that the kinetic energy lost in an inelastic collision due to conservation of momentum is equal to the energy absorbed in deformation of the colliding objects. Any collapse model that treats these as separate energy sinks is double-counting an energy loss.

Dave

 

[funk de fino]

.So how important is it with only 5 uses in 10,000 pages?

psik

How important is your name?

 

[Newtons Bit]

I guess that explains why the floor height increase for the mechanical floors begins one floor below the floors designated 'mechanical'.

I'm being self-contradictory and femr2 caught me. I wonder if I do the same thing at work...

Oh, and previous I put that the moment diagram is a curve with an exponential slightly <1, I should have put slightly >1. I am a doofus.

Femr2: how much of beam theory do you understand?

 

[psikeyhackr]

Beware: mathematics lies ahead.

.
Oh, I'm so SCARED!!!

For example, a frictional force between the two blocks would have exactly the same effect. This means that Heiwa's repeated assertion that entanglement and friction will arrest the collapse is a red herring. That entanglement and friction still factors into the conservation of momentum calculation, and is still a force that has to be transmitted to the lower structure. If that lower structure can't stop the fall of the upper block, invoking entanglement and friction won't help.

To summarise: Simple Newtonian dynamics demonstrates that the kinetic energy lost in an inelastic collision due to conservation of momentum is equal to the energy absorbed in deformation of the colliding objects. Any collapse model that treats these as separate energy sinks is double-counting an energy loss.

Dave

.
Great idea, use mathematics to come up with a rubbish conclusion.

I notice that no one has commented on the changes in collapse times resulting from varying the distribution of mass in FALL OF PHYSICS.

http://www.centerforinquiry.net/forums/viewreply/52039/

But I point out that FALL OF PHYSICS is "magical", meaning there are no physical supports to be broken. No energy is lost breaking them. Therefore there is no FRICTION between moving masses and masses being held stationary by supports. My FALL OF PHYSICS uses the same conservation of momentum. I just don't use that impressive delta and function BS.

But I knew that I wasn't bringing in the ENERGY LOSSES involved in BREAKING SUPPORTS which had to be considerable in a supposed top down collapse of the WTC, so talking about the energy losses due to conservation of momentum is just silly. I was simply demonstrating that mass alone would slow the collapse so obviously having to break supports would slow it even more.

My point was that we need to know the distribution of mass.

What was your point besides impressing and confusing people with math?

http://www.youtube.com/watch?v=LXAerZUw4Wc

The collapse was arrested much faster with mass than without. But the energy requirement to break the toothpicks was a significant factor. Where is that energy loss in your brilliant mathematics?

psik

 

[FineWine]

.
Oh, I'm so SCARED!!!


.
Great idea, use mathematics to come up with a rubbish conclusion.

I notice that no one has commented on the changes in collapse times resulting from varying the distribution of mass in FALL OF PHYSICS.

http://www.centerforinquiry.net/forums/viewreply/52039/

But I point out that FALL OF PHYSICS is "magical", meaning there are no physical supports to be broken. No energy is lost breaking them. Therefore there is no FRICTION between moving masses and masses being held stationary by supports. My FALL OF PHYSICS uses the same conservation of momentum. I just don't use that impressive delta and function BS.

But I knew that I wasn't bringing in the ENERGY LOSSES involved in BREAKING SUPPORTS which had to be considerable in a supposed top down collapse of the WTC, so talking about the energy losses due to conservation of momentum is just silly. I was simply demonstrating that mass alone would slow the collapse so obviously having to break supports would slow it even more.

My point was that we need to know the distribution of mass.

What was your point besides impressing and confusing people with math?

http://www.youtube.com/watch?v=LXAerZUw4Wc

The collapse was arrested much faster with mass than without. But the energy requirement to break the toothpicks was a significant factor. Where is that energy loss in your brilliant mathematics?

psik

You are incapable of learning from people who are highly qualified to instruct you. The reason is that you desperately want to pretend that you are their peer. Clearly, you are not. Why not drop the pose, the childish sneering, the uninformed arrogance, and try to learn something?

 

[psikeyhackr]

You are incapable of learning from people who are highly qualified to instruct you. The reason is that you desperately want to pretend that you are their peer. Clearly, you are not. Why not drop the pose, the childish sneering, the uninformed arrogance, and try to learn something?

.
You seem think I care about egoistic drivel but I notice you haven't explained what is incorrect about FALL OF PHYSICS.

What did he say about the energy required to break supports if what he wrote was so instructive? LOL

psik

 

[funk de fino]

.
You seem think I care about egoistic drivel but I notice you haven't explained what is incorrect about FALL OF PHYSICS.

What did he say about the energy required to break supports if what he wrote was so instructive? LOL

psik

Thats some high horse you have there.

What is important about your name?

 

[Dave Rogers]

What was your point besides impressing and confusing people with math?

Demonstrating that a specific fallacy that's been repeated by different truthers is, in fact, a fallacy. Most recently it's been asserted in this thread by femr2, so it seemed a reasonable point to clear up.

You clearly feel offended that I was addressing someone other than you; sorry, but there are other people in the world.

Dave

 

[femr2]

Femr2: how much of beam theory do you understand?

I'm not an expert. Why ?

Demonstrating that a specific fallacy that's been repeated by different truthers is, in fact, a fallacy. Most recently it's been asserted in this thread by femr2, so it seemed a reasonable point to clear up.

You clearly feel offended that I was addressing someone other than you; sorry, but there are other people in the world.

Dave

Download

Updated version of the calculation model with the following changes:

* Removal of focus on Greening paper, column usage replaced by values which are constant.
* Inclusion of conservation of momentum energy loss for usage in subsequent deformation of materials.
* Specific floor heights used, rather than an averaged constant.
* Concrete crush scale maximum removed. Unlimited scale permitted.
* Manual concrete crush scale ramping parameters removed.
* Impact KE based concrete crush scale calculation added. Switchable.
* Floor-by-floor concrete crush volume percentage added.
* Floor-by-floor mass loss (kg) added. Switchable.
* Per floor Impact KE based mass loss calculation added. Switchable.
* Calculated mass switchable to include/exclude cap mass loss.
* Initial cap drop height modifier added.
* Average Debris Lateral Ejection Velocity included.
* Debris Lateral Ejection Energy Requirement Added. (Applied to mass lost)
* Concrete mass inside core uses floor-by floor specific area percentage modifier to account for variation in usable floor area.
* Graphs for tracking Kinetic Energy, Mass and Velocity.

Note: Values are intended to be changed. Preset values are just for example.

 

[Dave Rogers]

* Inclusion of conservation of momentum energy loss for usage in subsequent deformation of materials.

I realised you'd already modified the model. I just thought it might be helpful to clarify the matter a little.

Dave

 

[Dave Rogers]

Secondly, notice that I didn't specify the internal mechanism by which the deformation force is exerted, and notice also that the actual value of that force drops out of the final numbers. It doesn't really matter how one block exerts a deformation force on the other - crushing, crumpling, buckling or whatever - only that it does. In fact, even variations in the value of that force in the course of the collision can be shown not to affect the final result (although that would take too much time and too much space on the forum; I'll leave it as an exercise to anyone who doesn't believe it).

Minor caveat: this is true of any force that opposes the relative motion of the blocks. It's not true of a force that may be exerted in the same direction as the relative motion. Hence, I'm not arguing against the existence of elastic collisions.

Dave

 

[aggle-rithm]

.
You don't seem to understand the difference between words and ideas.

Creating complicated words for simple ideas is NOT intellectually impressive. It is just pseudo-intellectual bullcrap on the part of people PRETENDING to be intelligent. Memorizing complicated jargon is just a time wasting BORE.

In programming we refer to this as a "ubiquitous language". It's absolutely essential for clear communication between domain experts and those who need to understand the domain.

(Although, ironically, I dislike the term "ubiquitous language" for the same reason you mention above; it's a complicated word describing, somewhat inaccurately, a simple idea. "Common language" would be better.)

 

[twinstead]

.
You seem think I care about egoistic drivel but I notice you haven't explained what is incorrect about FALL OF PHYSICS.

What did he say about the energy required to break supports if what he wrote was so instructive? LOL

I would be careful about accusing others of egoistic drivel; hypocrisy is a bad thing.