Merged Core-led collapse and explosive demolition

[Animal]

Teacher, I know it I know it! May I, pleeeeaaase? *snips finger excitedly
*

ETA: by the way, you knock out 33% of the columns, but only 25% of the load bearing capacity, assuming that all columns have the same "safety factor". Maybe ergo will pick up this hint when he does his calculation

You don't have to knock out ANY columns, all you need to do is remove enough lateral support and the columns will fail from their existing loads.

 

[Dave Rogers]

Where did you study engineering?

Never mind engineering, this is junior school level geometry.

Dave

 

[Oystein]

You don't have to knock out ANY columns, all you need to do is remove enough lateral support and the columns will fail from their existing loads.

We'll get that in Structural Engineering 102. Ergo and I are currently in SE101

 

[Animal]

We'll get that in Structural Engineering 102. Ergo and I are currently in SE101

I never had Structures 102. Ours was divided into Wood Structures, Steel Structures, and Concrete Structures......all taught by Aeronautical Engineering Profs.......who hated architects.

 

[Grizzly Bear]

I never had Structures 102. Ours was divided into Wood Structures, Steel Structures, and Concrete Structures......all taught by Aeronautical Engineering Profs.......who hated architects.

When I took them it was divided the same way except steel and concrete were formatted into one semester. They changed it to wood, steel, and concrete each having one semester dedicated after I finished my bachelors degree. And now they have students building reinforced concrete beams and they have to calculate the load bearing capacity, they then place the beams under a hydrolic press to test it out and validate their calcs.

 

[ergo]

Ozeco, the scenario you describe in post #938 is very much what occurred on the wall where the plane crashed through. So what, indeed, happened to that wall?

Grizzly, I did you the favour of reading through both your posts, and I notice you still haven't answered my two simple questions. A little puzzling since you claim to have studied engineering. This is what we get when we ask a direct question of bedunkers. Pointing away and blathering about self-evident, generic engineering principles. We're talking about a specific situation here. I expect a specific answer.

 

[beachnut]

Ozeco, the scenario you describe in post #938 is very much what occurred on the wall where the plane crashed through. So what, indeed, happened to that wall?

Grizzly, I did you the favour of reading through both your posts, and I notice you still haven't answered my two simple questions. A little puzzling since you claim to have studied engineering. This is what we get when we ask a direct question of bedunkers. Pointing away and blathering about self-evident, generic engineering principles. We're talking about a specific situation here. I expect a specific answer.

Where did you go to engineering school?

 

[Clayton Moore]

Very simple: The building was not designed to accommodate independent movement of any floors. It was designed to handle a static load.



Actually, I have it dead on. What I'm describing is a large mass in motion, carrying a huge amount of momentum, colliding with something that is not designed to stop it effectively.



At best you would see an decrease in acceleration. But it could be so small as to be unnoticeable.

The greater the discrepency between momentum and resistance, the less you will see resistance. In order to predict whether you would see deceleration, you would have to know both the momentum and the resistance. Your problem is that you don't know either number.

http://science.howstuffworks.com/engineering/structural/wtc2.htm

In the end, they designed the towers so they could sway about 3 feet in either direction.

 

[DGM]

http://science.howstuffworks.com/engineering/structural/wtc2.htm

Clueless.

I bet you think that link is relevant to what he said.

 

[aggle-rithm]

http://science.howstuffworks.com/engineering/structural/wtc2.htm

Funny, I saw nothing in that link about floors being designed to move independently of each other.

 

[Grizzly Bear]

<delete> Duplicate post

 

[Grizzly Bear]

Pointing away and blathering about self-evident, generic engineering principles.

You haven't even seen a temperature curve for structural steel let alone any tangible experience understanding how a structural assembly works. Your debate is done if you can't demonstrate you've studies any of it... It's obviously far from "self-evident" to you.

Your questions are for all practical purposes worthless because you're basing them on totally irreverent assumptions.

"85% intact structure"

"2/3 G"

No effort whatsoever to answer how the structure was built, how the columns are supposed to resist a falling mass that is not hitting the structure cleanly, nothing. You cannot arbitrarily assign percentages to quantify the remaining strength in a buildings supports. They aren't always uniform and they were'nt the same between the core and perimeter columns of the WTC. Your assumption precludes that all loads have a direct, evenly distributed path to the ground, with no eccentricity when the case in point is nothing near you "ideal" assumption."

Simply put your question has little bearing with reality.

You also created a silly strawman that fire has to fail something on the spot... You make your inexperience way too easy to spot.

 

[ergo]

"85% intact structure"

"2/3 G"

No effort whatsoever to answer how the structure was built, how the columns are supposed to resist a falling mass that is not hitting the structure cleanly, nothing.

Well, now you're getting close to one of the questions I asked. Given that tilt in WTC1 was at most one degree, and an estimated 85% of the columns in the impact zone were intact, i.e., continuous, the question is: How would the columns of the upper portion be "hitting" those of the lower portion unevenly at collapse initiation? Let's start with that.

 

[dafydd]

Ozeco, the scenario you describe in post #938 is very much what occurred on the wall where the plane crashed through. So what, indeed, happened to that wall?

Grizzly, I did you the favour of reading through both your posts, and I notice you still haven't answered my two simple questions. A little puzzling since you claim to have studied engineering. This is what we get when we ask a direct question of bedunkers. Pointing away and blathering about self-evident, generic engineering principles. We're talking about a specific situation here. I expect a specific answer.

Where did you study engineering? I expect a specific answer.

 

[ozeco41]

Teacher, I know it I know it! May I, pleeeeaaase? *snips finger excitedly
*

Try this:

______############
______Higher Levels
______##of Building#
______############
______|_____|_____|
______|_____|_____|
______|_____|_____|
______|_____|_____|
______|_____|_____|

______A____B____C
______0___400____0

...ETA: by the way, you knock out 33% of the columns, but only 25% of the load bearing capacity, assuming that all columns have the same "safety factor". Maybe ergo will pick up this hint when he does his calculation

Yes. And in this example the Row B loading doubles.

(Could the engineering pedants please remember:
1) I did say first order approximation;
2) We are illustrating a principle;
3) As Oystein says it is SE101; AND
4) No I have not forgotten about the flexibility if the upper structure - keep that for when/if we deal with the second order effects. )

 

[Animal]

Taking a 12 ft floor to floor height (conservative number) for the towers.......with a 208 ft width, the upper block pivoting @ the perimeter wall would mean that the opposing wall would impact one floor below a little over 4 feet "off center" and at the mid point of the building would be a little over 8". This means the structure would be impacting the floor slab, not the center line of the columns below. Failure of the structure is a given.

 

[Grizzly Bear]

To add... Connected columns aren't the problem; When the structure begins to buckle it's carrying capacity is dramatically reduced, and once failure begins it's rapid. It doesn't help with the bolted connections between columns and the perimeter either since they were subjected to out-of-plane loading (which helps to create moment forces) well beyond what they were designed to handle in the first place.

If that's for whatever reason confusing then think of it this way; which is easier? Holding a 20 pound weight directly overhead, or holding the same weight with your arm extended outward? With columns it's the same principal.

 

[Oystein]

Ozeco, the scenario you describe in post #938 is very much what occurred on the wall where the plane crashed through. So what, indeed, happened to that wall?
...

Uhm, ergo? I am pretty sure ozeco posed this question to YOU more than anyone else, even though his post #935 (#938 is my quote of it) was in reply to GrizzlyBear. It is obvious from the debate here that GrizzlyBear has at least basic understanding of engineering, but that you do not.

Now ozeco presented the answer. Could you please check it out and tell us if you agree? Taking out 25% of the load bearing capacity doubles the load on the next row of columns in that illustration?

Once you have affirmed this, I would you like you to ponder what that means for the twin towers, as you assert that this "is very much what occurred on the wall where the plane crashed through".

 

[ozeco41]

...Now ozeco presented the answer. Could you please check it out and tell us if you agree? Taking out 25% of the load bearing capacity doubles the load on the next row of columns in that illustration?...

IMNSHO, and after about 4 years trying to explain the WTC Twin Towers collapses to both engineers and non engineers, I think that understanding how the initial collapse occurred is the key. (Both collapses were essentially similar)

In turn the trick to understanding initial collapse is to recognise that it was a cascading dynamic process with two "not so obvious to the lay person" characteristics.

The first is to realise that load redistribution is not a question of linear reallocating whatever proportion of columns is lost at any stage. The "Three Column Model" illustrates a basic principle. The reality is much more complicated and understanding goes to an appreciation of the effective section modulus of the total structure and how that modulus changes as columns are cut or otherwise fail. Bottom line is that more load is transferred to some of the remaining columns when any single column fails than would appear from simple linear re-apportioning of the loads across all the remaining columns.

Second is to understand that the collapse initiation was a "cascade" or a "snowballing" process. With apologies for the inappropriateness of "snowballing" in the blazing fire setting of WTC.

The simple model to think about is tearing open a zip fastener. If you take the two sides of a zip fastened garment and attempt to pull them apart by grasping handfuls of the middle section of the garment the zip fastener will not yield. However start at one end of the zip and it will easily pull apart tooth by tooth.

Translating that visual model into the equivalent for multiple column failures is challenging even for a strongly NLP "Visual" like myself. So the other 80% of the population may need a lot more words.

 

[DGM]

Try this:

______############
______Higher Levels
______##of Building#
______############
______|_____|_____|
______|_____|_____|
______|_____|_____|
______|_____|_____|
______|_____|_____|

______A____B____C
______0___400____0

Yes. And in this example the Row B loading doubles.

(Could the engineering pedants please remember:
1) I did say first order approximation;
2) We are illustrating a principle;
3) As Oystein says it is SE101; AND
4) No I have not forgotten about the flexibility if the upper structure - keep that for when/if we deal with the second order effects. )

It's even conceivable that (A) could be in tension.