So who the heck ever said "Pull it" was slang for controlled demolitions?

Originally posted by samkent
If I may suggest a point.

If the trusses were overloaded with debris from another floor and or plane parts then they will sag. Regardless of the fire.
If the exterior columns were severed by the plane AND the trusses were overloaded would you not expect the exterior to be pulled inward below the cut point?
As per the picture.

Absolutly NOT. The building would bend to the exterior and fall from that point.
Like a hunk of your icecream cone.

Originally posted by ANOK
Do you have another one, because we are running out pretty quick here?

Yep. First, I have to say that I disagree with the concept that the sagging is caused by thermal expansion. I think sagging can really only be explained by a substantial failure or weakening of the trusses due to fire or other damage.

Second, your claim about the relative sizes of the columns and the trusses is misconceived. The trusses are oriented perpendicularly to the plane of the exterior columns/ chex grid, and are thus well placed to bow the perimeter columns, given a force to do so. Sounds hard to believe, but bear with me. Imagine for a moment a circus performer wearing a pair of old fashioned wooden stilts- little more than long slender sticks of wood. They are adequate to bear the performer's weight, and then some, as he takes giant steps from the top of one raised platform to the next. Nevertheless, when he later takes the pair of stilts and lays them like a bridge from one platform to another, the stilts break when he attempts to walk across them. Or consider how difficult it is to snap a common pencil by pushing down on it's eraser onto a table along its length... and how easy it is to snap when pushing with a finger across its length. The situation of the columns vs. the trusses is similar. Not only that, but the floor assembly (slab and trusses) were designed specifically to brace the perimeter columns against wind loads- the columns depend on the floors to maintain their straight vertical orientation- this becomes important later on.

Third, we need not rely solely on the inward pulling by the trusses to explain the full deformation we see just before the collapse, indeed we just need the trusses to stop bracing the columns against inward buckling, and give them a slight (by comparison) pull inward that bows the perimeter columns a bit Once this is accomplished, the load of the structure above will put more and more stress on the columns, which are not designed to bear loads when bent. Remember the pencil from pt. 2? How easy it was to snap when pushing across it's length?, and how hard when pushing along its length? Now take a pencil and balance it against a table top, eraser side up. Press down on the eraser with your palm. Usually, it won't give. But if you take a finger from the other hand, and push across the length of the pencil so that it bends a bit, you'll suddenly find that you can keep it bowed just by maintaining some pressure with the upper hand.

I find this to be a decent analogy for the processes at work in the perimeter columns immediately before collapse.

reply to post by hooper

Is that fact connected to the fact that not all building collapses have been caught on video? There's not one single video of me walking up the stairs in my house - does that mean I've never been to the second floor in my own home?

That is a fair enough point. It is hard enough to find non-controlled demolitions that look like itself much less a CD. Any descriptions though? Any body writing about it? However, the uncanny similarities between WTC7 and known CD's is at least enough to plant the seeds of doubt.

reply to post by thedman

Purpose of CD is to contain the rubble and break it up to make easier to haul away. Any fool can collapse a building - it is in getting the debris to fall in particular direction that is the real skill

True. Did it or did it not essentially fall right into it's footprint? That is my point with this issue in the first place. The collapse is just to perfect to have been accidental.

reply to post by coyotepoet


So what was "perfect" about the collapse of WTC 1,2, 7...?

Far from collapsing in "footprint" as often been claimed the debris from these buildings was thrown for
hundred of feet causing severe damage to adjacent structures

Collapse of WTC 1 damaged WTC 7 (350 ft away), smashed Winter Garden and hit World Financial Center
over 400 ft away

WTC 2 smashed 130 Liberty St (Deutsche Bank) and damaged it so severely had to be torn down. 90 West
St was set on fire, burning for for 2 days Only heavy masonry construction saved it

WTC 7 damaged Verizon building next door and caused partial collapse of 30 West Broadway (Fiterman
Hall) across street - it was torn down

The chaotic collapse of these buildings resulted in massive damage to all the adjacent buildings....

Originally posted by DrEugeneFixer

Or consider how difficult it is to snap a common pencil by pushing down on it's eraser onto a table along its length... and how easy it is to snap when pushing with a finger across its length.
I find this to be a decent analogy for the processes at work in the perimeter columns immediately before collapse.

Quote by dreugenefixer

Now take a pencil and balance it against a table top, eraser side up. Press down on the eraser with your palm. Usually, it won't give. But if you take a finger from the other hand, and push across the length of the pencil so that it bends a bit, you'll suddenly find that you can keep it bowed just by maintaining some pressure with the upper hand.

Dr, Dr you have this all upside down.
Now go get your pencil.
Ok got it? Put the eraser side down. Firmly apply pressure with your left hand. Palm down.
Now like the force of a hammer. Slam your left with your right hand.
The pencil WILL NOT BEND, not to much.
cheers ljb

edit on 4/16/2012 by longjohnbritches because: (no reason given)

Originally posted by Fluffaluffagous

Originally posted by ANOK

When steel heats up it expands, do you agree?

When steel expands it gets bigger, do you agree?

When it expands that expansion has to go somewhere, do you agree?

NIST agrees with this. They state that the expanding trusses pushed out the ext columns about an inch or two. An independent study done by truthers agrees.

That expansion causes the sagging, do you agree?

That sagging is a result of the steels expansion, do you agree?

If the steel sags due to it's expansion, it's because it has nowhere else to go, do you agree?

No to all.

So if it sags, because it has nowhere else to go

Incorrect premise. the trusses are able to initially push out the ext columns. this happens at 300-400C IIRC, before they sag.

then where is the pulling force coming from? How are the trusses putting any more force on the columns than it already did.

As the trusses further heat up, they begin to sag, and the columns pull back in. FEA and known properties of steel prove this.

And the question you all ignore, why didn't the 5/8", and 1", bolts fail before the obvioulsy more massive columns did?

Cuz the truss pull are not the only reason that the ext columns buckle. Read the NIST report. It shows that the core columns shortened first, from plane impacts and creep. the loads came off the core columns as a result and were redistributed to the ext columns, mainly in the center dozen or so, by the hat truss. the ext columns were also heated by the fires. In summary, several factors are responsible for the pull in.

Incorrectly representing the problem from NIST shows that you are either dishonest or ignorant of what you are arguing against.

Thought I would repost this for ANOK, since I see he's looking for an explanation of thr truss behavior in the fires.

reply to post by Fluffaluffagous


It has occured to me you are fluff and anok is chasing your fluff or his own tail.
Neither of you two have said SQUAT.
Especially when it comes to LARRY.AND PULL IT.
fraud mummmble, mummble, shills , mumble ,mumble.

reply to post by longjohnbritches

It has occured to me you are fluff and anok is chasing your fluff or his own tail.
Neither of you two have said SQUAT.
Especially when it comes to LARRY.AND PULL IT.
fraud mummmble, mummble, shills , mumble ,mumble.

Yeah, it's pretty much the same way over in the Chemtrail threads except with a different core group of characters.

Originally posted by longjohnbritches

It has occured to me you are fluff and anok is chasing your fluff or his own tail.
Neither of you two have said SQUAT.
Especially when it comes to LARRY.AND PULL IT.
fraud mummmble, mummble, shills , mumble ,mumble.

SQUAT.

Happy now?

reply to post by longjohnbritches


Typical reply from someone who has no argument.

Originally posted by samkent
If I may suggest a point.

If the trusses were overloaded with debris from another floor and or plane parts then they will sag. Regardless of the fire.
If the exterior columns were severed by the plane AND the trusses were overloaded would you not expect the exterior to be pulled inward below the cut point?
As per the picture.

Did you still not read and understand why sagging trusses cannot and WILL NOT put a pulling force on the columns?

So what if there was debris on the floors? once again you fail to understand factors of safety, and why the floors could hold much more weight, pressure, than what they normally would hold.

Not only that but the weight would not make the sagging trusses pull in the columns, if the weight did do anything it would simply cause the trusses to sag more. Why would SAGGING trusses have any energy to pull in massive columns. Deny ignorance, don't embrace it just to try to win an argument.

This is such common sense, it baffles me why you can't see the obvious.

A question, do you think it's true that a building by design must have more resistance in its structure than it has energy available to overcome that resistance?

Originally posted by thedman
reply to post by coyotepoet

 

So what was "perfect" about the collapse of WTC 1,2, 7...?

Far from collapsing in "footprint" as often been claimed the debris from these buildings was thrown for
hundred of feet causing severe damage to adjacent structures

Collapse of WTC 1 damaged WTC 7 (350 ft away), smashed Winter Garden and hit World Financial Center
over 400 ft away

WTC 2 smashed 130 Liberty St (Deutsche Bank) and damaged it so severely had to be torn down. 90 West
St was set on fire, burning for for 2 days Only heavy masonry construction saved it

WTC 7 damaged Verizon building next door and caused partial collapse of 30 West Broadway (Fiterman
Hall) across street - it was torn down

The chaotic collapse of these buildings resulted in massive damage to all the adjacent buildings....

No one had ever collapsed a building anywhere near 110 stories previous to 911. There's a reason why areas are cleared around controlled-demolitions, usually much more than "hundreds of feet" even for small buildings. The reason? They are not "perfect". They are "controlled". Perfect is a relative word in these situations when the results are compared to what would happen in an uncontrolled collapse.

130 Liberty Street was not torn town because of damage, it was torn down (beam by beam) because of toxic mold. And while you mention it, that building had very bizarre damage... a photo was taken of one of the beams that was hit by the south tower debris and the severed end of it was melted and twisted like a corkscrew. Evidently that jet fuel had even more magical properties than we thought. It managed to keep the pools of steel in the ground zero bathtub molten for several weeks.

I don't know how you OS'ers persevere.... it's like bailing out of the Titanic with a shot glass.

reply to post by ANOK

Why would SAGGING trusses have any energy to pull in massive columns. Deny ignorance, don't embrace it just to try to win an argument.

It's not the sagging per se it's the lack of lateral support from the exterior columns severed above the floor in question.
Once the trusses do sag for what ever reason they will torque the exterior column inward.

Originally posted by samkent
It's not the sagging per se it's the lack of lateral support from the exterior columns severed above the floor in question. Once the trusses do sag for what ever reason they will torque the exterior column inward.

No they wouldn't. You are simply describing the same thing using different words.

The floors braced the outer mesh during wind loading, they didn't hold the columns up, they did that by themselves. A failure of a floor assembly is not going to cause the mesh columns to do anything.

Sagging trusses would not have the energy to either pull in, or torque, the much more massive columns. How many more times are you going to ignore the physics of expanding materials? If the truss sags in the first place, it means it is not putting any force on the columns, pulling in or 'torquing'. If it was able to put a force on the columns it would have pushed columns out as it expanded, but it couldn't so they would sag because that is the only path of no resistance. If you added weight to the sagging truss, it would simply sag more.

One floor assembly by itself is not bracing the columns, failure of one floor would not cause the columns to become unstable.

And once again even IF they did it would not cause complete collapse of the building.

Do you agree that a buildings structure, must by design, have more resistance to collapse than it has energy to overcome that resistance to collapse? So how can a building collapse from its own mass? The factors of safety alone would make that impossible. You could place a whole other WTC tower on top and it would be able to hold the weight, because safety factors for steel building is 4-6.

Factor of safety (FoS), also known as (and used interchangeably with) safety factor (SF), is a term describing the structural capacity of a system beyond the expected loads or actual loads.

en.wikipedia.org...

A building can hold more weight than they are required to hold during its service life. So it is impossible for it's own weight to cause it to collapse.

In fact if you really cared about this you could demonstrate this easily, and prove it once and for all. Set up a light weight steel beam between two larger upright steel beams solidly fixed, and see it you can get them to be pulled in by heating up the light weight horizontal beam. I'd love to see your results.

reply to post by ANOK

If it was able to put a force on the columns it would have pushed columns out as it expanded....

No it wouldn't. Without a free end in the truss, the section had to choices - sag or summit. Up or down. With all the weight of the concrete above (which was also expanding by the way) it sagged. Gravity won. As it usually does. The sagging floor system pulled on the columns and the exterior construction. The rest you saw in the video.

Originally posted by ANOK
No they wouldn't. You are simply describing the same thing using different words.

The floors braced the outer mesh during wind loading, they didn't hold the columns up, they did that by themselves. A failure of a floor assembly is not going to cause the mesh columns to do anything.

Sagging trusses would not have the energy to either pull in, or torque, the much more massive columns. How many more times are you going to ignore the physics of expanding materials? If the truss sags in the first place, it means it is not putting any force on the columns, pulling in or 'torquing'. If it was able to put a force on the columns it would have pushed columns out as it expanded, but it couldn't so they would sag because that is the only path of no resistance. If you added weight to the sagging truss, it would simply sag more.

So according to professor ANOK, all those engineers at NIST, all those engineers and scientsits who performed experiments that show that heated sagging trusses exert a pull in force are all wrong. And all this because professor ANOK is incapable of understanding a very simple concept in physics.

One floor assembly by itself is not bracing the columns, failure of one floor would not cause the columns to become unstable.

And once again even IF they did it would not cause complete collapse of the building.

Do you agree that a buildings structure, must by design, have more resistance to collapse than it has energy to overcome that resistance to collapse? So how can a building collapse from its own mass?

By weakening the structure by crashing Boings into is an let it burn for some time.

The factors of safety alone would make that impossible. You could place a whole other WTC tower on top and it would be able to hold the weight, because safety factors for steel building is 4-6.

Factor of safety (FoS), also known as (and used interchangeably with) safety factor (SF), is a term describing the structural capacity of a system beyond the expected loads or actual loads.

en.wikipedia.org...

A building can hold more weight than they are required to hold during its service life. So it is impossible for it's own weight to cause it to collapse.

In fact if you really cared about this you could demonstrate this easily, and prove it once and for all. Set up a light weight steel beam between two larger upright steel beams solidly fixed, and see it you can get them to be pulled in by heating up the light weight horizontal beam. I'd love to see your results.

edit on 4/17/2012 by ANOK because: (no reason given)

So you still don't grasp the difference between static load and dynamic load, after it being explained dozens of time. And you asked for proof that you are clueless about physics? Can you show me anyone who has a background in physics who does not agree that your display in this thread is proof beyond any doubt that you are clueless?

Originally posted by hooper

No it wouldn't. Without a free end in the truss, the section had to choices - sag or summit. Up or down. With all the weight of the concrete above (which was also expanding by the way) it sagged. Gravity won. As it usually does. The sagging floor system pulled on the columns and the exterior construction. The rest you saw in the video.

Hmmm no, it is because it was pinned between columns that it could not push out as the steel lengthened from expanding, so it sags instead.

If it could not push columns out, it will also not pull columns in, the force required is the same, that simple. Gravity is not going to cause sagging trusses to put a pulling force on the columns, it doesn't work that way.

The weight of the concrete, sagging or not, would not do anything. The trusses were designed to hold that weight more than once over due to FoS. The trusses could have held more than the weight of two floors easily with an FoS of 4-6.

BTW you still haven't answered my question about the 5/8" and 1" bolts? When are you going to explain that contradiction? You always accuse me of ignoring your questions, so where is your answer to my question hopper?

Why do you keep ignoring what I'm saying, so I have to keep repeating myself? Trying to wear me down?

reply to post by ANOK

BTW you still haven't answered my question about the 5/8" and 1" bolts? When are you going to explain that contradiction? You always accuse me of ignoring your questions, so where is your answer to my question hopper?

Its Hooper. I don't purposely distory your screen name.

What's the question?

The floor system (not just the trusses) sagged. The sagging changed the relationship between the trusses, their connections to the columns and the columns.

Why The Columns Pulled In

ANOK, with all sincerity I wanted to find the best way to have this explained. The following is an explanation with math. This was written by a SE. I hope this clears things up.

Why did the columns bow in? There’s been quite a bit of speculation and misinformed opinion about the mechanics of the structure that caused that, so I hope to do a little bit of enlightenment. The first thing that needs to be looked at is the problem. Figure 1 shows a typical building section through a building such as the WTC towers.
bp0.blogger.com...
Figure 1

Everything here is fairly straight forward. The gravity load path can be seen very easily. The floor trusses deliver the vertical floor loads to the columns which deliver them to the foundations. But what happens when a core column is severed as in Figure 2?

bp0.blogger.com...
Figure 2
Things start to get a little bit more complicated. The first thing that should dawn on most people is that the floor is no longer being supported by the middle column which is going to cause some problems. The middle column will drop unless there is a force that can resist it, see Figure 3.
bp1.blogger.com...
Figure 3


As the column drops, the top chord of the floor truss develops tensile forces (it is quite literally stretched). This tensile force has two parts, a vertical portion that pulls the column up and a horizontal force that pulls the rest of the structure in. This can be seen in Figure 4.


bp2.blogger.com...
Figure 4


The other things to note here is that the left column is still under its full axial loading (P2, which will be important in the analysis). The left column is already shown pulled in to some degree, however it is not to scale. Further modifying the problem, we know that the fires caused the trusses to sag to some degree. If the fire is hot enough, the truss will become a tension only member. This means that the top chord of the truss will act something like a rope and pull inwards at its connections. This can be seen in Figure 5. There is another condition as well (which I have no illustrated) that will cause the heated floor to expand outwards without losing its bending capacity and thus not sagging. It is a condition that likely proceeded that of the sagging floor trusses.

bp3.blogger.com...

NIST (1-6D) estimates that the total pull-in force at the exterior columns is roughly 6 kips (6,000lbs) at each column. The truss to column connection consisted of (2) 5/8” diameter bolts. Even non-structural grade bolts of this size will have a shear capacity of over 5kips each, so it is reasonable to assume that the top chord of the truss will not pull off of the columns at the connections due to a 6kip load.

Is this 6 kips enough to pull the column in several feet as seen in the photos of the tower?
bp0.blogger.com...

Math is needed here. First some assumptions need to be made. For the purpose of this analysis, let the exterior column be HSS14x14x5/16 tubes at 25% of the maximum axial load prior to any damage. The column has the following properties:

Similar to HSS 14x14x5/16
A = 15.7in^2
I = 739 in^4
S = 92.3 in ^3
Pn = 557k (from AISC LRFD 3rd, table 4-6 with an unbraced length, KL = 12’-4”)
Pu = ¼* 557k = 139k
Mn = 92.3in^3*46ksi = 4645 kip*in (Mn = maximum bending capacity)

The column itself will bend inwardly until it snaps if the column itself ever becomes inelastic. This can be defined by the ratio (I’ve simplified this a bit): Mu/Mn + Pu/Pn < 1. The other limit state is P-delta. When the exterior column is pulled inwards, it deflects. This deflection(Δ) generates a moment, specifically P2*Δ. This moment, creates more deflection, which further magnifies the moment, creating more moment, and so forth. P-delta has two outcomes: the moment reaches equilibrium at some point, or becomes unstable and continues to grow. This phenomenon can be easily shown with a simple experiment. Take a straw and try to compress it between your fingers. It has a surprising amount of strength. Now push the middle in slightly. This is p-delta.

We know that the floor diaphragm along the wall were greatly damaged due to fire and the impact of the aircraft. Let us assume that there are two floor diaphragms that are damaged to the point that they no longer provide bracing against buckling. There is thus a pull-in force of 6kips at two places along the length of the column.

bp0.blogger.com...
CALCULATION 1: DIAPHRAGM DAMAGE, NO FIRE EFFECTS
Unbraced length = 37’-0”
Pu = 139k
Pn = 465k (from AISC LRFD 3rd, table 4-6 with an unbraced length, KL = 37’-0”)
Mn = 4645 kip*in

Mu = P*a
Mu = 6kip*1/3*37ft
Mu = 74kip*ft