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WTC7 and the girder walk-off between column 79 and 44

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Christopher7 said:
No, we are talking about the fact that the girder was NOT pushed off its seat because:
1) the seat was 12" wide not 11" wide and
2) the girder had stiffeners that would have prevented the bottom flange from folding and
3) even if the beams could push the girder completely off the seat it would only drop 1" to the support plate.

NIST said the girder expanded until it pressed against column 79 so the top and bottom flanges would hit the side plate after about 4" of travel.

[qimg]http://img853.imageshack.us/img853/9758/col79stiffenerse.jpg[/qimg]

No, that was found to be a preliminary test and not the final cause. You got to the party late and you missed a lot.
Click to expand...


So Chris7, what did NIST have to say when you showed them this?:rolleyes:
 
Christopher7 said:
No, we are talking about the fact that the girder was NOT pushed off its seat because:
1) the seat was 12" wide not 11" wide and
2) the girder had stiffeners that would have prevented the bottom flange from folding and3) even if the beams could push the girder completely off the seat it would only drop 1" to the support plate.

NIST said the girder expanded until it pressed against column 79 so the top and bottom flanges would hit the side plate after about 4" of travel.

[qimg]http://img853.imageshack.us/img853/9758/col79stiffenerse.jpg[/qimg]

No, that was found to be a preliminary test and not the final cause. You got to the party late and you missed a lot.
Click to expand...


Really? and you have done the math to confirm that or are you just guessing?
 
Christopher7 said:
No, we are talking about the fact that the girder was NOT pushed off its seat because:
1) the seat was 12" wide not 11" wide and
2) the girder had stiffeners that would have prevented the bottom flange from folding and
3) even if the beams could push the girder completely off the seat it would only drop 1" to the support plate.
NIST said the girder expanded until it pressed against column 79 so the top and bottom flanges would hit the side plate after about 4" of travel.

[qimg]http://img853.imageshack.us/img853/9758/col79stiffenerse.jpg[/qimg]

No, that was found to be a preliminary test and not the final cause. You got to the party late and you missed a lot.
Click to expand...


Only? how do you know that? The math for coming to that conclusion would be quite complex as there are many variables. Lets see your math so we can verify your conclusion.:rolleyes:
 
Christopher7 said:
No, we are talking about the fact that the girder was NOT pushed off its seat because:
1) the seat was 12" wide not 11" wide and 2) the girder had stiffeners that would have prevented the bottom flange from folding and
3) even if the beams could push the girder completely off the seat it would only drop 1" to the support plate.

NIST said the girder expanded until it pressed against column 79 so the top and bottom flanges would hit the side plate after about 4" of travel.

[qimg]http://img853.imageshack.us/img853/9758/col79stiffenerse.jpg[/qimg]

No, that was found to be a preliminary test and not the final cause. You got to the party late and you missed a lot.
Click to expand...

No it wasn't!

It was 8 1/4 wide! IIRC?
 
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LSSBB said:
Can't move laterally?

Say, what happens if one floor has slabs move due to expansion, and the one above it doesn't?
Click to expand...
You forgot that we are talking about one floor and the column moving in relation to the girder. The floor beams and slab were being heated on the east side pushing west but the column could not move that way because of the continuous slab. NIST said the exterior wall did not move at all because that would take up some of the expansion.

This brings up an interesting point. Concrete expands about 85% as much as steel so when the beams had expanded 5" the slab would have expanded about 4 1/4". It couldn't move 250' of slab from column 79 to the other end of the building so it had to push the exterior wall out.
 
Christopher7 said:
You forgot that we are talking about one floor and the column moving in relation to the girder. The floor beams and slab were being heated on the east side pushing west but the column could not move that way because of the continuous slab. NIST said the exterior wall did not move at all because that would take up some of the expansion.

This brings up an interesting point. Concrete expands about 85% as much as steel so when the beams had expanded 5" the slab would have expanded about 4 1/4". It couldn't move 250' of slab from column 79 to the other end of the building so it had to push the exterior wall out.
Click to expand...

It certainly does! All those fires and concrete and steel. All that movement. All those failures. Lots happening, right?

Your explosives & thermite?
 
Christopher7 said:
You forgot that we are talking about one floor and the column moving in relation to the girder. The floor beams and slab were being heated on the east side pushing west but the column could not move that way because of the continuous slab. NIST said the exterior wall did not move at all because that would take up some of the expansion.

This brings up an interesting point. Concrete expands about 85% as much as steel so when the beams had expanded 5" the slab would have expanded about 4 1/4". It couldn't move 250' of slab from column 79 to the other end of the building so it had to push the exterior wall out.
Click to expand...

The slabs would not have expanded at the same rate (time) as the beams.
 
Christopher7 said:
No, that was found to be a preliminary test and not the final cause. You got to the party late and you missed a lot.
Click to expand...
I also came late to the party, but not enough as to miss this:

tfk said:
Now, why don't you re-read NCSTAR1-9, Section 8.8, where NIST describes exactly the failure mode that their model predicts.
Click to expand...

So I went there and read, and found this:

The predicted response of the system is summarized in Table 82. The first failures observed were of the shear studs, which were produced by axial expansion of the floor beams, and which began to occur at fairly low beam temperature of 103 °C. Axial expansion of the girder then led to shear failure of the bolts at the connection to Column 79; and, at a girder temperature of 164 °C, all four erection bolts had failed, leaving that end of the girder essentially unrestrained against rotation. Continued axial expansion of the floor beams pushed the girder laterally at Column 79, as shown in Figure 826, in which failed shear studs and bolts were evident. When the beam temperatures had reached 300 °C, all but three shear studs in the model had failed due to axial expansion of the beams, leaving the top flanges of the beams essentially unrestrained laterally. Continued axial expansion of the girder caused it to bear against the face of Column 79, generating large axial forces that led to failure of the bolts connecting the girder to Column 44. When the girder temperature had reached 398 °C, all four erection bolts at Column 44 had failed, leaving the girder essentially unrestrained against rotation at both ends. After failure of the erection bolts in the seat at Column 44, continued axial expansion of the floor beams pushed the girder laterally, where it came to bear against the inside of the column flange. Axial compression then increased in the floor beams, and at a beam temperature of 436 °C, the northmost beam began to buckle laterally. Buckling of other floor beams followed as shown in Figure 8-27 (a), leading to collapse of the floor system, and rocking of the girder off its seat at Column 79 as shown in Figure 8-27 (b). The collapse process took time to occur in the LS-DYNA analysis, during which the temperatures had ramped up to their maximum values in the simulation.
​

That is from the FINAL report.
 
pgimeno said:
...
That is from the FINAL report.
Click to expand...

He has been told this. But C7 takes the "technical briefing" as even more final when it mentioned "walking off", and that it trumps the report. Because, ummm, it suits him to say so.

Personally I'd say the briefing just got sloppy (or, at least, one person did).

Meanwhile there are many circumstances that could lead the girder to fall. One obvious one (mentioned by tfk, and maybe others) is sagging/buckling followed by cooling. That girder only has 2" max to go to be off the 2" plate below the seat, the one that's really doing the work ....
 
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pgimeno said:
I also came late to the party, but not enough as to miss this:


​

So I went there and read, and found this:

The predicted response of the system is summarized in Table 82. The first failures observed were of the shear studs, which were produced by axial expansion of the floor beams, and which began to occur at fairly low beam temperature of 103 °C. Axial expansion of the girder then led to shear failure of the bolts at the connection to Column 79; and, at a girder temperature of 164 °C, all four erection bolts had failed, leaving that end of the girder essentially unrestrained against rotation. Continued axial expansion of the floor beams pushed the girder laterally at Column 79, as shown in Figure 826, in which failed shear studs and bolts were evident. When the beam temperatures had reached 300 °C, all but three shear studs in the model had failed due to axial expansion of the beams, leaving the top flanges of the beams essentially unrestrained laterally. Continued axial expansion of the girder caused it to bear against the face of Column 79, generating large axial forces that led to failure of the bolts connecting the girder to Column 44. When the girder temperature had reached 398 °C, all four erection bolts at Column 44 had failed, leaving the girder essentially unrestrained against rotation at both ends. After failure of the erection bolts in the seat at Column 44, continued axial expansion of the floor beams pushed the girder laterally, where it came to bear against the inside of the column flange. Axial compression then increased in the floor beams, and at a beam temperature of 436 °C, the northmost beam began to buckle laterally. Buckling of other floor beams followed as shown in Figure 8-27 (a), leading to collapse of the floor system, and rocking of the girder off its seat at Column 79 as shown in Figure 8-27 (b). The collapse process took time to occur in the LS-DYNA analysis, during which the temperatures had ramped up to their maximum values in the simulation.
​

That is from the FINAL report.
Click to expand...

Yes, the rock off theory. Almost the opposite from their walk off theory. So which is it that you believe, was it pushed off, or pulled off?
 
gerrycan said:
I suppose you would have to define failure. NIST for example would appear to disagree with you, maybe their definition of failure is different to yours. Mine is too.
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Do you understand the claim tfk was making or not? If so, why did you ask him to explain?
 
gerrycan said:
Yes, the rock off theory. Almost the opposite from their walk off theory. So which is it that you believe, was it pushed off, or pulled off?
Click to expand...
Why do you keep asking debunkers what they "believe" instead of actually making points?
 
gerrycan said:
I'm asking which NIST explanation sounds like the most probable to have occurred. The point is that there is a choice.
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No, you're asking them which explanation (?) they think occurred, not discussing which is most probable. You're spinning wheels.

You are going to respond to 554, right?
 
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gerrycan said:
Yes, the rock off theory. Almost the opposite from their walk off theory. So which is it that you believe, was it pushed off, or pulled off?
Click to expand...

Both are plausible, among others, so they are not "opposites" at all. The NIST final report reckoned "rock off".

It's good that you're taking your work to YouTube. That's the right place for it.
 
Christopher7 said:
You forgot that we are talking about one floor and the column moving in relation to the girder. The floor beams and slab were being heated on the east side pushing west but the column could not move that way because of the continuous slab. NIST said the exterior wall did not move at all because that would take up some of the expansion.

This brings up an interesting point. Concrete expands about 85% as much as steel so when the beams had expanded 5" the slab would have expanded about 4 1/4". It couldn't move 250' of slab from column 79 to the other end of the building so it had to push the exterior wall out.
Click to expand...

What you have now, Chris, is a Boundary Value problem. One side is fixed. And it's still a 3-dimensional problem - other floors expanding at different rates. So what does this do to your narrowed focus to one girder and it's seat? These things all interrelate. This is why an FEA is necessary to solve the problem, not just Excel and drawings.

ETA: So where's the weakest link?
 
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