Merged Core-led collapse and explosive demolition

[Oystein]

There's no such thing as a gravity collapse of buildings the size of WTC 1, 2, and 7.

You expect them to remain suspended in mid-air once supports fail?
How about if you knock out all columns with explosives - will the buildings remain suspended in mid-air? If not, why not? What happens?

 

[beachnut]

Gravitational acceleration



http://en.wikipedia.org/wiki/Gravitational_acceleration

ROTFL

Disregarding 80 floors of building resistance!!!


ahahahhahahah

You posted proof you are wrong. Do you comprehend physics? You posted proof of how the WTC collapse works due to gravity.

 

[Clayton Moore]

You expect them to remain suspended in mid-air once supports fail?
How about if you knock out all columns with explosives - will the buildings remain suspended in mid-air? If not, why not? What happens?

How would you expect supports to fail in the pristine building beneath the plane's point of impact?

Oh yeah, that's right, gravitational acceleration. ahahahahahahahhahahahaha

 

[Oystein]

How would you expect supports to fail in the pristine building beneath the plane's point of impact?

Oh yeah, that's right, gravitational acceleration. ahahahahahahahhahahahaha

Easy.
Collapse initiated in the not-so-pristine impact- and fire zone.
Once the 15 (30) above that zone start moving down, they exert a dynamic load on the yet untouched structure below that it was not designed to handle.

It's the same principle CD specialists apply when they rig a building with explosives: They get a part of the building to turn lose, and then gravity takes over and does the rest.
In a typical controlles demolition, 90% and more of the energy that's used to destroy the building comes from gravity.
It doesn't really matter much what the initiating event is - fire, explosives, plane, earthquake or a platoon of midgets with see-saws. Once enough columns fail, it's gravitational collapse.

This is where E=mgh (potential energy) and E = 1/2mv² (kinetic energy) come into play - physics formulas you consider to be "insanity".

Clayton, may we learn at this point which level of school education you have reached so far? I learned about the different kinds of energy in 12th grade.

 

[Animal]

How would you expect supports to fail in the pristine building beneath the plane's point of impact?

Quite simple. The load imposed on the remaining structure exceeds the yield point of the remaining structure. This load exceeds the yield point of the remaining structure through a combination of dynamic loading (which far exceeded the static loading), eccentrically loading, loading imposed on secondary structures not designed to carry such loading, and the failure of secondary structures resulting in overloading of other structures due to unbraced conditions.

Oh yeah, that's right, gravitational acceleration. ahahahahahahahhahahahaha

The laugh of ignorance.

 

[TheRedWorm]

how would you expect supports to fail in the pristine building beneath the plane's point of impact?

Oh yeah, that's right, gravitational acceleration. Ahahahahahahahhahahahaha

ahem:

what would you expect to happen? How should the buildings have collapsed?

i do not see that you answered the question.

What would you have expected to happen and why?

These structures are the first skyscrapers to have globally collapsed primarily due to fire but fire was simply not the only factor in wtc 1&2. The fires began attacking a structure that had already suffered significant damage.

You guffaw at the idea that a tilted object falls straight down. You are demonstrating a pretty complete ignorance of physics.

Only if the tilted object can continue to rotate will it fall over to one side. However if the pivot point is destroyed then this object will fall straight down. Its center of mass will no longer be able to travel horizontally once that opivot is gone..

 

[ergo]

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.

You not only don't know how to answer the question, you don't even know how to fake it.

 

[TheRedWorm]

He wasn't responding to a question, and what he posted makes sense, especially when he summed up the thrust of the post with a very simplified example in the last paragraph. What, exactly, is inadequate about Grizzly's post?

 

[ergo]

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.

What degree of tilt are you positing here? Do you have some evidence to confirm it? We are talking about WTC1 here. Secondly, How did you arrive at your "off-center" distances?

 

[Grizzly Bear]

You not only don't know how to answer the question, you don't even know how to fake it.

Ergo, the entire premise of your question is faulty; I explained why it was faulty. Several people followed up to explain why it was faulty. I challenge that the entire premise behind your question being out of touch with reality renders it fruitless.You made it obvious that you're winging it with out any of the most fundamental understanding of engineering or architecture, and you made a conscious choice to not look into any of it yourself independently with existing literature. If you think any of what I said was wrong in my earlier posts the floor is yours to tell everyone what I got wrong... according to you. Source it.

Or will you simply ignore the challenge to your question's premise and respond with a condescending tone how I didn't answer your "question" again?

I'm guessing the latter

 

[ergo]

No, Grizzly, you have neither answered the questions, which were originally posed to Myriad, nor have you explained your own attempted response. I even simplified it here for you.

It's this continual avoidance of specific examination that makes arguing with bedunkers so tedious. But the more people see how they can't answer the questions, the more they'll be likely to investigate it for themselves.

 

[beachnut]

No, Grizzly, you have neither answered the questions, which were originally posed to Myriad, nor have you explained your own attempted response. I even simplified it here for you.

It's this continual avoidance of specific examination that makes arguing with bedunkers so tedious. But the more people see how they can't answer the questions, the more they'll be likely to investigate it for themselves.

You have some interesting points, what engineering school did you gain all this expertise to analysis the WTC collapse?

 

[jaydeehess]

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.

Are you questioning the cause of initial collapse or of continued, global collapse?

If its the later and we take this up After initial collapse then its quite obvious that the upper and lower sections of columns are no longer in line. If they were then they would have to be falling through themselves.


Given then that they are not in line then all but a small percentage of dynamic forces from falling mass is going to impinge upon the floorspace, NOT the columns.
The ONLY way for forces to be transferred to columns from floorspace is via the trusses and their seats on the columns. These elements were never designed to hold the dynamic forces, nor the static load, of a dozen or more storeys of the structure and thus fail quickly barely slowing the falling mass and indeed adding mass to that falling debris.

No floors and trusses for several floors = no lateral support for core columns = long column failure (not to mention severe buffeting and the violent tearing away of said lateral support)

 

[jaydeehess]

How would you expect supports to fail in the pristine building beneath the plane's point of impact?

Oh yeah, that's right, gravitational acceleration. ahahahahahahahhahahahaha

Are you questioning the cause of initial collapse or of continued, global collapse?

If its the later and we take this up After initial collapse then its quite obvious that the upper and lower sections of columns are no longer in line. If they were then they would have to be falling through themselves.


Given then that they are not in line then all but a small percentage of dynamic forces from falling mass is going to impinge upon the floorspace, NOT the columns.
The ONLY way for forces to be transferred to columns from floorspace is via the trusses and their seats on the columns. These elements were never designed to hold the dynamic forces, nor the static load, of a dozen or more storeys of the structure and thus fail quickly barely slowing the falling mass and indeed adding mass to that falling debris.

No floors and trusses for several floors = no lateral support for core columns = long column failure (not to mention severe buffeting and the violent tearing away of said lateral support)

my post applies to you as well CM

 

[Newtons Bit]

Quite simple. The load imposed on the remaining structure exceeds the yield point of the remaining structure. This load exceeds the yield point of the remaining structure through a combination of dynamic loading (which far exceeded the static loading), eccentrically loading, loading imposed on secondary structures not designed to carry such loading, and the failure of secondary structures resulting in overloading of other structures due to unbraced conditions.

The word you're looking for is "capacity", not "yield point". Yield in engineering terminology refers to the yield stress of a material. The yield stress it not reached in compression members that have lost bracing.

The laugh of ignorance.

You may not want to gloat too much...

 

[Clayton Moore]

Are you questioning the cause of initial collapse or of continued, global collapse?

If its the later and we take this up After initial collapse then its quite obvious that the upper and lower sections of columns are no longer in line. If they were then they would have to be falling through themselves.


Given then that they are not in line then all but a small percentage of dynamic forces from falling mass is going to impinge upon the floorspace, NOT the columns.
The ONLY way for forces to be transferred to columns from floorspace is via the trusses and their seats on the columns. These elements were never designed to hold the dynamic forces, nor the static load, of a dozen or more storeys of the structure and thus fail quickly barely slowing the falling mass and indeed adding mass to that falling debris.

No floors and trusses for several floors = no lateral support for core columns = long column failure (not to mention severe buffeting and the violent tearing away of said lateral support)

Nothing dynamic about a building that can sway three feet at a minutes notice.

Soooo no need to bother with controlled demolitions. Just a strategic heating of the steel is all that's necessary.

 

[TheRedWorm]

There is nothing predictable about crashing an airplane into a building. Also, do you actually understand the concept of dynamic load?

 

[leftysergeant]

Nothing dynamic about a building that can sway three feet at a minutes notice.

Problem is that the collapse had little to do with the vertical supports. Just dump enough heavy crap onto one floor all at once and they will all pop loose to the ground floor.

This is, of course, removing the structure that held up the outer was, so those unpeel likea banana skin. Then there is nothing to hold up the core, which shivers a bit, breaking connections and falls mstly straight down or leaning over a bit.

The fact that it broke apart from top-down kept it from falling sideways.

 

[jaydeehess]

Nothing dynamic about a building that can sway three feet at a minutes notice.

Soooo no need to bother with controlled demolitions. Just a strategic heating of the steel is all that's necessary.

Apparently you do not understand what I am referring to by 'dynamic forces'.

I am referring NOT to horizontal forces that would cause a building to sway(i.e. wind). I am referring in this case (and it should have been pretty damned obvious for anyone with English as a native language) to the focre of impact of the falling mass upon the floor trusses which would have to be transferred to columns via the truss seats.

Further more your query concerned how the 'pristine' lower portion could have been destroyed. I answered that. Now you shift and dodge and want to know how the heating caused the initial collapse.

OK, fine.

Aircraft impact severs or damages most perimeter columns on one side, a few on the far side and several core columns. Some floor panels are also dislodged by impact. The structure thus begins the fire phase with these structural elements no longer effective.

Impact also removes large amounts of passive fire protection thus increasing the speed of heat transfer to those areas of structural elements that are now unprotected against fire.


Impact spreads liquid accelerant throughout several floors and ignites immediate large area fires involving the office contents on several levels. This is a condition that has never occured in any office structure. This is a condition (large area multi-level fires) that in more common fire situations takes hours to develop. In the towers it took literally seconds.

Fires continued to spread both to previously uninvolved areas on the initial fire floors and to higher floors as well.

As columns heated they lost strength and with a load on them were constrained from linear expansion. This caused them to 'creep', which in turn caused adjacent columns to have more load on them. As the fires spread and more columns experienced heat weakening. The increasing load and sagging floors caused perimeter columns to buckle. A point was the reached when loads being redistributed put some columns into complete failure requiring another load redistribution which caused more column failures in a very rapid sequence.

Initial collapse occured.
Global collapse ensued as in my above post.

In other words, no , simple strategic heating of the steel would not cause the structure to fail.
It required that passive fire protection be compromised alowing faster heating of the steel
AND
thousands of gallons of liquid accelerant spread out on several floors to ignite large area fires within seconds(as opposed to hours)
AND
it was aided by the initial removal of structural elements by the impact of the aircraft.

Clear now?

 

[Newtons Bit]

How would you expect supports to fail in the pristine building beneath the plane's point of impact?

Oh yeah, that's right, gravitational acceleration. ahahahahahahahhahahahaha

It's pretty simple.

The plane impact severed/damaged a large number of perimeter and core columns. The structure must deform to redistribute the compression loads from these columns to the rest of the structure. This is simple for the perimeter columns, as they are part of a moment frame. The interior core columns was less so. The severed columns deflected downwards, which put the floor trusses connecting these columns into tension. About 4 kips of inward pulling was delivered to each column. The structure was able to handle these loads. However the columns lost stiffness as the fire progressed which resulted in a p-delta failure mode. I've done the math showing this.

Once the collapse initiated, failure becomes inevitable. This can be explained through a method called "enveloping the solution" that engineers typically use to analyze complex problems. Two (sometimes more) sets of assumptions are created that define limit states of the problem. In the case of the WTC progressive collapse, the two limit states are (1)perfect column axial strikes and (2)the columns of the upper-block and lower-block completely miss each other and instead strike floors. (1) has been shown to result in a progressive collapse. (2) obviously results in a collapse as the upper-block weighs several times more than the capacity of a single floor.