WTC Discussion: Core Column Temperature & Failure.

[28th Kingdom]

So what happened to the core columns once the outer columns failed and transferred all the different loads over to the core columns? Did all of the core columns buckle? If not, how did they break and fall within the downward collapse?

Thanks.

 

[Architect]

I can give you a technical response to that, but you do tend to ignore them.

 

[aggle-rithm]

I used video footage plus scientific laws to debunk NIST's theory.

Using a scientific law to prop up the short leg of the couch doesn't count.

 

[babazaroni]

I'm so glad you showed up. Look, I have a little present for you:

http://youtube.com/watch?v=-RzwmD8uB8g

Remember, how you said the outer columns failed...and the trusses remained attached to them? Well, here is NIST's own computer simulation...and looky at what happens when the outer columns break. Whoopsie.

He said the trusses remain attached in order to pull the columns in.

The trusses remain attached until the columns break.

What do think will happen to trusses attached to columns that break in a catastrophic way?

You seem to have a problem with sequence of events analysis.

When somebody says something about a particular event in a sequence of events, and it changes in the next event, that is not, to use your favorite term, DoubleSpeak

 

[babazaroni]

So what happened to the core columns once the outer columns failed and transferred all the different loads over to the core columns? Did all of the core columns buckle? If not, how did they break and fall within the downward collapse?

Thanks.

Get to your point.

You want us to give you an analysis so you can do your semantic twist DoubleSpeak and run dance.

 

[Mr. Skinny]

I can give you a technical response to that, but you do tend to ignore them.

Architect, if you don't mind offering that response, I'd appreciate it.

Personally, I can think of several potential failure modes, and several of those in combination, but I'm not in the structures business, so I defer to those smarter than me.

 

[defaultdotxbe]

Architect, if you don't mind offering that response, I'd appreciate it.

Personally, I can think of several potential failure modes, several of them in combination, but I'm not in the structures business, so I defer to those smarter than me.

i second that, id like to here architects take on it too

 

[28th Kingdom]

Remember, according to NIST only 10 of the core columns on WTC 2 were severed, which leaves 37 non-severed core columns with only one having heavy damage. So the sagging trusses are what buckled the outer columns...and this took a while to do...so once the load from the upper mass was fully transferred over and bearing straight down on the 37 non-severed columns (which, by the way...only showed a max temp of 250C according to NIST. I realize, they didn't have paint samples to test every core column, however, the hottest ones they found were right at 250C (a temp that has very little weakening effect on steel) so why would we assume the other core columns were hotter than the ones they analyzed?) how did the 37 core columns all start buckling in the span of one second....apparently continuing to buckle and snap at every floor, all the way down some 80+ floors. How can we explain this?

Thanks.

 

[babazaroni]

Remember, according to NIST only 10 of the core columns on WTC 2 were severed, which leaves 37 non-severed core columns with only one having heavy damage. So the sagging trusses are what buckled the outer columns...and this took a while to do...so once the load from the upper mass was fully transferred over and bearing straight down on the 37 non-severed columns (which, by the way...only showed a max temp of 250C according to NIST. I realize, they didn't have paint samples to test every core column, however, the hottest ones they found were right at 250C (a temp that has very little weakening effect on steel) so why would we assume the other core columns were hotter than the ones they analyzed?) how did the 37 core columns all start buckling in the span of one second....apparently continuing to buckle and snap at every floor, all the way down some 80+ floors. How can we explain this?

Thanks.

When the outer columns buckle, you lose the load bearing support of over 200 columns.

Do you really expect a damaged core is now going to hold all this moving mass?

Not even an undamaged core can do this.

The moving mass will also not come down perfectly vertical and will cause lateral movement of the core. We know the core was not designed for lateral loads. That was the job of the outer columns.

 

[Architect]

Skinny, Default

No problem.

It is important to understand that the 3 key structural elements - outer columns, floors, and inner core - all act together as a big girder in order to achieve overall structural stability. A space frame might be a better analogy, albeit one that had a central member.

The loss of any one element - for example the floors - is therefore going to result in the loss of (at its most basic) the bracing effect on the adjacent inner & outer columns and leave them vulnerable to collapse.

In short, we couldn't build the core alone as a freestanding steel framed object using those size of columns, if at all, because there simply isn't enough to hold it all together.

Now if we add to that the impact damage and destabilisation caused by the failure of the floors, we're going to see failure - probably along the joint connections - pretty much straight away. That some small elements (I think particularly of Christophera's "spire" ) lasted up to 15 seconds is quite a surprise One can postulate the survival of cross-bracing and semi-independent floor plates in the area may have helped, but we'd have to see the fabrication drawings.

Does that help?

 

[babazaroni]

Architect, don't forget the Hat Truss as a key element. This is what transferred the load to the core after the outer columns broke.

 

[Architect]

Architect, don't forget the Hat Truss as a key element.

You are entirely correct in terms of the overall collapse, as it served to stave off the fateful moment by restributing the loads prior to failure. I was only referring to the survival (or otherwise) of an intact freestanding core, which is (frankly) laughable.

 

[Mr. Skinny]

Skinny, Default

(snip)

Does that help?

Architect, so sorry.

I guess I was trying to imagine how the steel core failed (once it started to let go, that is), and was thinking ... well, torsion, compression, shear or combinations of those things perhaps. That's more along the line of what I was looking for.

 

[Architect]

Architect, so sorry.

I guess I was trying to imagine how the steel core failed, and was thinking ... well, torsion, compression, shear or combinations of those things perhaps. That's more along the line of what I was looking for.

But there's no evidence that it was the core columns which were the key failure mechanism or hinge point; instead we look at the floors and outer columns. Once they go, there's nothing supporting the core and it fails. Depending on locaiton it could be shear, compression, or any variation thereon.

Assuming that the loads continued to transfer onto the core, they would have surpassed design capacity and failed in many, many ways - buckling, exacerbated by the lack of transverse support/bracings as floors fail, for example.

 

[Mr. Skinny]

But there's no evidence that it was the core columns which were the key failure mechanism or hinge point; instead we look at the floors and outer columns. Once they go, there's nothing supporting the core and it fails. Depending on locaiton it could be shear, compression, or any variation thereon.

Assuming that the loads continued to transfer onto the core, they would have surpassed design capacity and failed in many, many ways - buckling, exacerbated by the lack of transverse support/bracings as floors fail, for example.

Gaah.. you quoted me before I made my edit to say "once things start to go" or sumptin like that.

I understand the collapse process, that is, load was transferred to the core. I'm just trying to understand what forces would be acting on the steel, and what failure modes might present themselves.

Sounds like it might be a mixture of failure modes, depending on the column location, etc.

Sorry again.

ETA: You answered my question quite nicely above. Thanks.

 

[stateofgrace]

Remember, according to NIST only 10 of the core columns on WTC 2 were severed, which leaves 37 non-severed core columns with only one having heavy damage. So the sagging trusses are what buckled the outer columns...and this took a while to do...so once the load from the upper mass was fully transferred over and bearing straight down on the 37 non-severed columns (which, by the way...only showed a max temp of 250C according to NIST. I realize, they didn't have paint samples to test every core column, however, the hottest ones they found were right at 250C (a temp that has very little weakening effect on steel) so why would we assume the other core columns were hotter than the ones they analyzed?) how did the 37 core columns all start buckling in the span of one second....apparently continuing to buckle and snap at every floor, all the way down some 80+ floors. How can we explain this?

Thanks.

This is a joke, right?

Are you being serious?

Have you not read a single thing that has been said to you?

The core did not snap on every floor. The floor spaces collapsed around the core .They collapsed because a whooping weight dropped on them. The FLOOR SPACES were ripped out from the core. The core or bits of it stood as the building collapsed around it. The core finally gave up after the floors and the external supports that braced it in place were gone.

It is simple 28th, it is not magic, it is not a mystery why NIST did not look beyond the collapse mechanism,they did not need to. It is obvious.
AGAIN>>>>>>>>>>>>>>>>>>>>>>>>>>

Weight falls on floors................Floors brace core and external supports together................Bracing is gone...............external support go as they are no longer braced to the internal core by the floors.................core collapses.

Now 28th since you believe the core did not survive but was actually snapped at each floor level, please offer up your proof.

 

[Minadin]

No problem.

It is important to understand that the 3 key structural elements - outer columns, floors, and inner core - all act together as a big girder in order to achieve overall structural stability. A space frame might be a better analogy, albeit one that had a central member.

The loss of any one element - for example the floors - is therefore going to result in the loss of (at its most basic) the bracing effect on the adjacent inner & outer columns and leave them vulnerable to collapse.

In short, we couldn't build the core alone as a freestanding steel framed object using those size of columns, if at all, because there simply isn't enough to hold it all together.

Now if we add to that the impact damage and destabilisation caused by the failure of the floors, we're going to see failure - probably along the joint connections - pretty much straight away. That some small elements (I think particularly of Christophera's "spire" ) lasted up to 15 seconds is quite a surprise One can postulate the survival of cross-bracing and semi-independent floor plates in the area may have helped, but we'd have to see the fabrication drawings.

Does that help?

That's a completely accurate portrayal from my experience, that's also nicely worded using simple terms that are easier to understand for the layman. Good job.

The floor systems provided lateral support for the core and the exterior columns. The core took the brunt of the vertical dead loads for the floors, while the exterior took most of the wind loads as well as the vertical loads. If you have any one of those systems fail, the other 2 cannot function anymore, and the structure will collapse.

 

[Architect]

Gaah.. you quoted me before I made my edit to say "once things start to go" or sumptin like that.

I understand the collapse process, that is, load was transferred to the core. I'm just trying to understand what forces would be acting on the steel, and what failure modes might present themselves.

Sounds like it might be a mixture of failure modes, depending on the column location, etc.

Sorry again.

ETA: You answered my question quite nicely above. Thanks.

We'd have to look very carefully at the design of the core; for example, were the floors within the core wholly seperate and thus providing a degree of cross bracing? Where was the general cross bracing?

The simplest explanation probably revolves around simple overloading and shear of the joints between columns, to be honest, but the simplest explanations are rarely the most accurate......

 

[Architect]

Just as an aside, are you guys aware of the (in)famous case of the Citicorp Building and the errant structural calculations? It's a fascinating account of just how complex the structural issues can be and the scope for errors......

 

[Mr. Skinny]

We'd have to look very carefully at the design of the core; for example, were the floors within the core wholly seperate and thus providing a degree of cross bracing? Where was the general cross bracing?

The simplest explanation probably revolves around simple overloading and shear of the joints between columns, to be honest, but the simplest explanations are rarely the most accurate......

Yeah, without having all of the specs for the building, it would be impossible for us to tell.

I suppose I was just looking for confirmation of that my guess that it would have been a very wide variety of failure modes on the steel. Almost chaotic, in a sense...compression with torsion then shear, for example, rather than some clean snap, snap, snap of members in identical failure modes.


ETA: Actually, I supose the lower floors which were not damaged by the aircraft impact and fire damage, would have experienced similar failure modes. I suppose I was more thinking of the steel failures on the fire/impact floors re. chaotic/combination failures.