big red bulls eye on the wtc in 9/11

[Uno Hoo]

That does look like a weak-ass floor truss design.

If I understand your explanation correctly, you are saying a number of floor trusses sagged, and failed, thus the perimeter columns buckled and failed. So we have both deformation (floor trusses and perimeter columns), and we also have the connections failing outright (breaking apart).

If anyone has any suggestions, I would greatly appreciate hearing them. I'm just wondering how weak the buildings must have been before and/or during the collapses.

The structural design of the twin towers was phenomenally strong before the impact. And what is lost upon a great many analysts is that the building code required design for floor loads which were in actual fact far heavier than those
existing at the time of impact or collapse. The floor structure was required to support a weight roughly translated as being the equivalent weight of one human standing on each square foot of floor. Considering the actual weight of furniture and the few people actually standing around at the moment of impact, and, at the moment of incipient collapse, the floor structure was actually supporting very little more than its own weight (always already accounted for by structural designers). The floor trusses were therefore stronger by a factor of something like ten or twenty than they needed to be. If we think of the time when they were supposedly weakened by heat soaking, and had lost half their strength, they were still stronger by a factor of five to ten than needed. If they sagged, they had little more than their own weight to use to tug upon the inner and outer columns. The inner and outer columns were designed to resist such inward tug (bedrock standard structural engineering practice since they were designed to resist the full maximum floor load).

The inner and outer columns were required by building code to be designed to resist the inward tug of a full floor load. The actual floor load was between one tenth and one twentieth of the designed floor load at the moment of impact or the moment of collapse.

The inner and outer columns supported gravity loads. In most cases, a column designed to support its gravity load will coincidently be innately able to support an inward tug far in excess of the tug provided by its floor trusses. The outer columns look as if they possessed such moment of inertia. They look as if they could have resisted an inward tug greatly more than the actually lightly loaded floor trusses provided.

The floor truss may look weak ass to somebody who has not worked professionally for years and years as a structural engineering designer. The perimeter columns may look weak ass to somebody who has not worked for years and years as a professional structural engineering designer.

Somebody who has many years of experience will tell you that the floor trusses looked very strong. Somebody who has many years of experience will tell you that the outer column design was phenomenally strong. And it is really hard to believe that the relatively small amount of damage done to the perimeter by the impact permitted collapse.

And it is really hard to believe that the supposed heat soaking eventually caused collapse. The heat would have been very rapidly dissipated throughout the outer column envelope. The outer columns could not have been raised to a high enough temperature to lose a significant amount of their strength.

I have some time ago examined the Pentagon crash also. I am amazed that the same class of airplane knocked virtually no holes in the Pentagon, but, knocked out patches of structural steel columns in the towers. Something is wrong with this picture.

 

[Uno Hoo]

the presence of butt joints in the perimeter columns point directly to a bad design. a full 1/3 of the joints in the perimeter were butt joints, one of the weakest joints known.

once the perimeter was compromised the building essentially "unzipped" itself.
an engineer that used to post here by the name of tony agrees with me on this point.

Only a genuine structural design amateur would say such a thing. Any and every joint in the structural design of any building has to carry and transmit the load. Every joint is analyzed to verify that it is transmitting the load. It does not matter if it is a butt joint or any other kind of joint. If it calculates to carry the load, it is OK.

 

[shaman_]

And it is really hard to believe that the supposed heat soaking eventually caused collapse. The heat would have been very rapidly dissipated throughout the outer column envelope. The outer columns could not have been raised to a high enough temperature to lose a significant amount of their strength.

Have you seen photos or video of the outer columns being pulled inward leading to the collapse?

I have some time ago examined the Pentagon crash also. I am amazed that the same class of airplane knocked virtually no holes in the Pentagon, but, knocked out patches of structural steel columns in the towers. Something is wrong with this picture.

At the pentagon the plane hit some light poles and the ground before colliding with the reinforced concrete walls.

 

[stereologist]

The floor trusses were therefore stronger by a factor of something like ten or twenty

Not even Boulder Dam was not that over engineered.

You've inflated the strength by an order of magnitude and misrepresented the damage done by the impact.

The outer columns look as if they possessed such moment of inertia.

What?

Somebody who has many years of experience will tell you

And who is this somebody? This is the sort of glittering generality that needs to be claimed.

The heat would have been very rapidly dissipated throughout the outer column envelope.

This is also a twoofer claim that isn't true.

 

[stereologist]

I have some time ago examined the Pentagon crash also. I am amazed that the same class of airplane knocked virtually no holes in the Pentagon, but, knocked out patches of structural steel columns in the towers. Something is wrong with this picture.

The plane hit the Pentagon and penetrated several reinforced concrete walls. That is substantially different from the WTC which was an open network of steel where the plane entered one side and some parts of it passed through the buildings.

Two very different types of buildings yield two very different results. No surprises there.

 

[sifreak21]

Sifreak, that is a genuine question.

The way it has been answered is the fact that the building in and of itself is 95% air. There is surprisingly little material compared to similar buildings.

Now remember that the exterior bars did not fail as badly as the central ones did. And when the center ones failed the floors above had more than enough empty space to implode on themselves

very true i didnt look at it that way

 

[fedr808]

Why do you feel the need to build a model? What do you believe happened on 9/11?

Don't just JAQ off...(just asking questions) Do you believe that 19 terrorists hijacked 4 planes, and flew them into buildings...or do you believe it was an "inside job"?

The problem you guys with building a model is because steel loses 1/2 its strength at 600 degrees, and in order to make an accurate model the fire inside would have to be 800 degrees, and that temperature would melt the entire model or set it on fire before the steel wire melted.

Anyways, theyve done tons of computer simulations and those are more accurate

 

[fedr808]

The structural design of the twin towers was phenomenally strong before the impact. And what is lost upon a great many analysts is that the building code required design for floor loads which were in actual fact far heavier than those
existing at the time of impact or collapse. The floor structure was required to support a weight roughly translated as being the equivalent weight of one human standing on each square foot of floor. Considering the actual weight of furniture and the few people actually standing around at the moment of impact, and, at the moment of incipient collapse, the floor structure was actually supporting very little more than its own weight (always already accounted for by structural designers). The floor trusses were therefore stronger by a factor of something like ten or twenty than they needed to be. If we think of the time when they were supposedly weakened by heat soaking, and had lost half their strength, they were still stronger by a factor of five to ten than needed. If they sagged, they had little more than their own weight to use to tug upon the inner and outer columns. The inner and outer columns were designed to resist such inward tug (bedrock standard structural engineering practice since they were designed to resist the full maximum floor load).

The inner and outer columns were required by building code to be designed to resist the inward tug of a full floor load. The actual floor load was between one tenth and one twentieth of the designed floor load at the moment of impact or the moment of collapse.

The inner and outer columns supported gravity loads. In most cases, a column designed to support its gravity load will coincidently be innately able to support an inward tug far in excess of the tug provided by its floor trusses. The outer columns look as if they possessed such moment of inertia. They look as if they could have resisted an inward tug greatly more than the actually lightly loaded floor trusses provided.

The floor truss may look weak ass to somebody who has not worked professionally for years and years as a structural engineering designer. The perimeter columns may look weak ass to somebody who has not worked for years and years as a professional structural engineering designer.

Somebody who has many years of experience will tell you that the floor trusses looked very strong. Somebody who has many years of experience will tell you that the outer column design was phenomenally strong. And it is really hard to believe that the relatively small amount of damage done to the perimeter by the impact permitted collapse.

And it is really hard to believe that the supposed heat soaking eventually caused collapse. The heat would have been very rapidly dissipated throughout the outer column envelope. The outer columns could not have been raised to a high enough temperature to lose a significant amount of their strength.

I have some time ago examined the Pentagon crash also. I am amazed that the same class of airplane knocked virtually no holes in the Pentagon, but, knocked out patches of structural steel columns in the towers. Something is wrong with this picture.

Uno, I may have given you the wrong impression. I wasnt so much implying that they failed just because of heat.

But because of the unequal distribution of heat, the bars literally bent and twisted in the building.

Now im pretty sure a floor truss is either directly or indirectly attached to the side columns and the central columns. Im willing to bet that if the trusses didnt snap in half (and some of the cross beams did look like they could do that) than the pins holding them probably would.

Because when you think about it, those pins were made to hold them securely in place on a flat even surface, they werent made for, say, one end of the floor being significantly higher than the other side.

 

[Neddy Bate]

The floor truss may look weak ass to somebody who has not worked professionally for years and years as a structural engineering designer. The perimeter columns may look weak ass to somebody who has not worked for years and years as a professional structural engineering designer.

Somebody who has many years of experience will tell you that the floor trusses looked very strong. Somebody who has many years of experience will tell you that the outer column design was phenomenally strong. And it is really hard to believe that the relatively small amount of damage done to the perimeter by the impact permitted collapse.

And it is really hard to believe that the supposed heat soaking eventually caused collapse. The heat would have been very rapidly dissipated throughout the outer column envelope. The outer columns could not have been raised to a high enough temperature to lose a significant amount of their strength.

Thanks for the detailed response, Uno Hoo. As a total layman, I did think the connections between the floor and the perimeter columns looked weak. That also means that I can't see how the floors could have pulled down any load bearing columns. It seems to me if some floors did fail, they would just land on the floors below them and stop there. That's why I am trying to find out how weak the structure was supposed to be at that point in time. Like you point out, was the heat soaking supposed to make the whole building weak all the way down to the ground? Or was the building still strong, at least toward the bottom, but the forces too much for it to handle anyway?

 

[Neddy Bate]

The problem you guys with building a model is because steel loses 1/2 its strength at 600 degrees, and in order to make an accurate model the fire inside would have to be 800 degrees, and that temperature would melt the entire model or set it on fire before the steel wire melted.

Anyways, theyve done tons of computer simulations and those are more accurate

So, if it were possible to make a model that would suffer a loss of strength on the order of about 50%, then a model could collapse fairly easily. Does the loss of strength have to be throughout the whole structure, or just in the general vicinity of the impact site? I mean, if the whole building is to collapse, would there have had to have been an ambient temperature of 800 degrees throughout the whole building?

 

[leopold]

Only a genuine structural design amateur would say such a thing. Any and every joint in the structural design of any building has to carry and transmit the load. Every joint is analyzed to verify that it is transmitting the load. It does not matter if it is a butt joint or any other kind of joint. If it calculates to carry the load, it is OK.

then it's funny that a mechanical engineer from NASA agrees with me on the points i made innit?

 

[leopold]

Thanks for the detailed response, Uno Hoo. As a total layman, I did think the connections between the floor and the perimeter columns looked weak.

the floors themselves did not carry any of the buildings weight.
the structural importance of the floors were to keep the building from twisting.

That also means that I can't see how the floors could have pulled down any load bearing columns.

the floors didn't pull on the core or the perimeter.
once the floors collapsed it allowed the core and perimeter to twist and bulge from the vertical.

It seems to me if some floors did fail, they would just land on the floors below them and stop there.

a few of the floors did exactly that, but the lower floors were not designed to support the load if itself plus 2 or 3 upper floors.

 

[stereologist]

Remember Neddy that the failure began not when 1 floor fell down on another, but when 20 floors fell down on another. The floors pancaked one after another.

 

[fedr808]

So, if it were possible to make a model that would suffer a loss of strength on the order of about 50%, then a model could collapse fairly easily. Does the loss of strength have to be throughout the whole structure, or just in the general vicinity of the impact site? I mean, if the whole building is to collapse, would there have had to have been an ambient temperature of 800 degrees throughout the whole building?

no, the problem with a model isnt that theyre trying to cover it up, but because the space is too small.

The reason it failed wasnt just the steel losing strength, they had planned for that, it was one side of the building being significantly hotter than the other and those steel beams expanded and twisted and stressed the other ones.

The only way to simulate that is to have the same floor space, which would defeat the purpose of a model

 

[Uno Hoo]

no, the problem with a model isnt that theyre trying to cover it up, but because the space is too small.

The reason it failed wasnt just the steel losing strength, they had planned for that, it was one side of the building being significantly hotter than the other and those steel beams expanded and twisted and stressed the other ones.

The only way to simulate that is to have the same floor space, which would defeat the purpose of a model

Generally speaking, the idea of making a physical model is the height of silliness. When a building structure is being designed, it is being modeled. It is being modeled in minute detail in the mind's eye of the engineers, and in the excruciatingly thorough mathematical calculations which ensue.

The concept of beams becoming weak from heat and simultaneously strongly expanding and twisting the columns is ludicrous, while they are also sagging and falling down. If they are turned into wet spaghetti from the heat, how can they give a strong push against a column? No way. Go drink a pot of strong coffee and think about it with a clear head. I vaguely remember an old joke having something to do with trying to shove a wet noodle up a wildcat's inopportunely small aperture. I forget the exact nature of the aperture.

 

[Dywyddyr]

Generally speaking, the idea of making a physical model is the height of silliness. When a building structure is being designed, it is being modeled. It is being modeled in minute detail in the mind's eye of the engineers, and in the excruciatingly thorough mathematical calculations which ensue.

That's all very nice, but unfortunately not true.
Which is why engineers do build models.
In many cases it's far easier to build a model to check things than it is to calculate them, especially if you want to find out how an unexpected load over there affects the structure over here.

 

[Uno Hoo]

the floors themselves did not carry any of the buildings weight.
the structural importance of the floors were to keep the building from twisting.

the floors didn't pull on the core or the perimeter.
once the floors collapsed it allowed the core and perimeter to twist and bulge from the vertical.

a few of the floors did exactly that, but the lower floors were not designed to support the load if itself plus 2 or 3 upper floors.

Every floor structure of the entire building was required by the building code to be designed to carry a load which was almost certainly around ten to twenty times the real actual load which was on it at the time of the impact or the time of the observed onset of collapse.

The perimeter column design of the towers was a revolutionary innovation. It essentially made the entire building be one integral column with a consequent huge moment of inertia. The loss of lateral bracing of one or two floor structures was truly a drop in a bucket. Every building in any jurisdiction is required to be structurally designed to resist lateral earthquake and wind loads which are considerable even in the most lenient township. In the absence of an earthquake or tornado, practically any building has enough lateral stability, coincident with its control of gravity loads, to be stable even if a great portion of its floor-provided lateral bracing is somehow removed.

I am a relatively patient man, but, it is absurd to read so much grossly uneducated structural design dreaming as is in this thread and practically every other thread about this subject anywhere. Structural engineering is one of the most hard nosed sciences on the face of this planet. Magic forces don't just pop up out of nowhere and twist around and do shit. Forces arise from very specific and totally predictable causes. Anybody who mouth offs and says that a floor truss will simultaneously sag too much to carry its own weight and at the same time will expand and irresistibly push over a phenomenally strong strong column network is hallucinating.

 

[Uno Hoo]

That's all very nice, but unfortunately not true.
Which is why engineers do build models.
In many cases it's far easier to build a model to check things than it is to calculate them, especially if you want to find out how an unexpected load over there affects the structure over here.

The only reason structural engineers build models is to do PR. I have actually done this engineering thing for a great many years. You obviously are a wannabe and a faker.

No professional structural engineer would ever sign off on a structural design on the basis of observations made from a model. The only acceptable procedure is to do calculations. I know this. You and any other faker wannabe do not know it.

 

[Uno Hoo]

P.S. There have been cases of architects doing wind tunnel tests of buildings to verify wind loads. Perhaps you are thinking of such.

 

[Dywyddyr]

The only reason structural engineers build models is to do PR. I have actually done this engineering thing for a great many years. You obviously are a wannabe and a faker.

And you're obviously clueless.
The idea that you can account perfectly for every force and load is utter nonsense.
The real world does not behave the same way that nice neat little graphs indicate it does.

No professional structural engineer would ever sign off on a structural design on the basis of observations made from a model. The only acceptable procedure is to do calculations. I know this. You and any other faker wannabe do not know it.

And you don't read either: at no point did I say that the design was signed off purely on the basis of model observations.
Calculation is an indicator, not a guarantee. Ask NASA (among others). Why is so much funding spent on wind-tunnel models (oh! aircraft AND buildings) if calculation tells you the whole story?

Wannabe?
I must be pretty good at faking it to last over 30 years as an engineer...