• Quick note - the problem with Youtube videos not embedding on the forum appears to have been fixed, thanks to ZiprHead. If you do still see problems let me know.

'What about building 7'?

Status
Not open for further replies.
pgimeno said:
What Animal said.

NIST took into account many kinds of failure modes, including torsional. There are a bunch of ways in which connections can survive even when the girder buckles. I'll leave them up for you to discover.
Click to expand...

Yeah, if I wanted the kind of education that teaches that attaining satisfactory convergence in ANSYS has nothing to do with load balance I would have came here.
If I wanted educated in how to make assertions about NISTs model that NIST fail to endorse, I would come here.
If I wanted the kind of education that gets figures wrong, attributes the wrong function to ANSYS elements and supposed that walk off was observed in ANSYS rather than being designated an arbitrary walk distance prior to and outwith the model, I would ask you directly.
 
Last edited:
During the last bunch of pages, it's been made clear that neither gerrycan nor Ziggi do want to accept for a second the possibility that the report is not flawed, and they keep trying hard to find new angles to see if the arguments fail under a new one.

That should make it transparent that their "scientific approach" is backwards: they start with the conclusion (that the building could not collapse due to fire) and try to find the data that confirms it.

That's what you do when you're driven by a political agenda and not by a sincere search for truth.
 
pgimeno said:
During the last bunch of pages, it's been made clear that neither gerrycan nor Ziggi do want to accept for a second the possibility that the report is not flawed, and they keep trying hard to find new angles to see if the arguments fail under a new one.

That should make it transparent that their "scientific approach" is backwards: they start with the conclusion (that the building could not collapse due to fire) and try to find the data that confirms it.

That's what you do when you're driven by a political agenda and not by a sincere search for truth.
Click to expand...

That's funny. What political motive could you possibly believe me to have regarding this? Please enlighten me... this should be good.
 
gerrycan said:
So at what point of the analysis would you expect to start seeing degrading of the connections at the ends of this girder (C79-80) ?
Click to expand...
Can you answer my question first?

DGM said:
I'd find that highly unlikely due to the condition present on that day. Wouldn't you?
Click to expand...

When are you going to deal with reality and stop trying to find fault with the NIST methods. Do you feel their fire estimates are also wrong?
 
Last edited:
DGM said:
Yes, 40 years ago (I'm 56)

To answer your question. I would expect degrading right away under the conditions.
Click to expand...

So why does NISTs model not exhibit any damage throughout the entire model at either of these connections?
 
gerrycan said:
So why does NISTs model not exhibit any damage throughout the entire model at either of these connections?
Click to expand...
Because the model is set to ignore damage that would cause premature failure (or contribute to non convergence) . The NIST also strengthened connections in their analysis. It's all part of knowing how to work with FEA to get meaningful results.
 
Last edited:
DGM said:
Because the model is set to ignore damage that would cause premature failure. The NIST also strengthened connections in their analysis. It's all part of knowing how to work with FEA to get meaningful results.
Click to expand...

No, the way to get meaningful results from a FEA is to input data which reflects the structural elements that make up the structure in an accurate way.
But, back to these 2 connections. You are saying that NIST deliberately over-rated the end connections on the C79-80 girder in order to avoid the element failing?
ETA are you sure you aren't getting confused with the outside girder connections that NIST took to be infinately strong?
 
Last edited:
gerrycan said:
No, the way to get meaningful results from a FEA is to input data which reflects the structural elements that make up the structure in an accurate way.
But, back to these 2 connections. You are saying that NIST deliberately over-rated the end connections on the C79-80 girder in order to avoid the element failing?
ETA are you sure you aren't getting confused with the outside girder connections that NIST took to be infinately strong?
Click to expand...
How many elements would it take to be "an accurate way"?

As far as "over-rating", yes. The NIST did in fact add strength to connections that was not there. This falls into judgement calls based on knowledge of the sym and data gained from experience and other data.
 
DGM said:
How many elements would it take to be "an accurate way"?
Click to expand...
Same as the amount they used. As you said yourself a few minutes ago, NIST attributed different characteristics to different connections. The decision to fail the C79-44 girder was taken outwith of ANSYS when the required walk distance was designated. Bad call on NISTs part.

DGM said:
As far as "over-rating", yes. The NIST did in fact add strength to connections that was not there. This falls into judgement calls based on knowledge of the sym and data gained from experience and other data.
Click to expand...
And did they release details of their "judgement calls" ? Do we have the chance to scrutinize these NIST estimates?
With the exception of making the outer girder connections infinitely strong, there is no way of quantifying anything that NIST did. But what is established is that NIST ignored elements in the crucial connection and also varied connection strengths on the strength of unpublished judgement calls.
 
How NIST determined girder C79-C44 on the 13th floor failed by fire

[FONT=&quot]1) [/FONT][FONT=&quot]NIST analyzes the northeast corner floor system to evaluate its response to elevated temperatures and to confirm which failure modes need to be accounted for in the 16-story and 47 stories models.[/FONT]​
[FONT=&quot] [/FONT]​
[FONT=&quot] “A finite element analysis of the northeast corner floor system was conducted to evaluate its response to elevated temperatures and to confirm which failure modes needed to be accounted for in the 16-story ANSYS model. ….. This analysis demonstrated possible failure mechanisms that were used to develop the leading collapse hypothesis further. The failure modes in this model were incorporated into the 16 story ANSYS and 47 story LS-DYNA analyses.[/FONT][FONT=&quot] (Section 8.8 pp.349,353)[/FONT]
[FONT=&quot]
[/FONT]​
[FONT=&quot]2) [/FONT][FONT=&quot]NIST determines C79-44 failed by lateral-torsional buckling in the one story and 16 story models.[/FONT]​
[FONT=&quot]Here is a paraphrased version of the most detailed explanation of how NIST described the failure of girder C79-44 for a one floor model in their report (NCSTAR 1-9, section 8.8, their pp. 349-354):
The expanding beams pushed the C79-44 girder to the west. The expanding girder jammed at C79 and C44. The beams continued to expand and were axially compressed by the resisting girder, buckling the beams. The sagging beams rotated the heated, buckled girder to the east. (See Figures 8-26, 8-27). At a certain rotated critical angle of the top flange, the girder failed to carry its load and fell. (Section 11.2.9, pp.487-488)[/FONT]
[FONT=&quot]“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)”[/FONT][FONT=&quot] (p. 353) See Figures 8-27(a,b).[/FONT]
[FONT=&quot]“If a beam or girder twisted half of its flange width laterally, it would not be able to support its gravity loads and would be removed from the analysis. “ [/FONT][FONT=&quot]In this girder case half of the W30x133 flange width = 5.25”[/FONT]
[FONT=&quot]
It should also be noted that whereas the attention has been focused on the seat at C79, this unrestrained girder condition at this seat was of an area of a few square inches whereas the twisting forces on the girder occurred over the entire ~44 foot girder, failing it as NIST noted in their lateral- torsional buckling analysis and figures.[/FONT][FONT=&quot][/FONT]

​
[FONT=&quot]3) NIST uses the one floor model findings in the 16 floor model section 11.4.1 and determines C79-44 failed by buckling.[/FONT]​
[FONT=&quot] “Thermal Effects on Floor Beams and Girders[/FONT]​
[FONT=&quot]The girder between Columns 26 and 81 buckled and walked off the bearing seat between 3.25 h and 3.5 h. In a similar fashion, the girders between Columns 79 and 80 and Columns 80 and 81 buckled and the girder between Columns 44 and 79 buckled and walked off the bearing seat between 3.7 h and 4.0 h. Girder buckling was due to the combined effects of (1) gravity loads from the floor beams, (2) lateral westward displacement due to the thermal expansion in the east floor beams, and (3) increased axial loads due to thermal expansion in the girder. “(p.527)[/FONT]

[FONT=&quot][/FONT][FONT=&quot][/FONT]
[FONT=&quot]4) [/FONT][FONT=&quot]In light of the buckled girder failure, how then is the following consistent?[/FONT]
[FONT=&quot][/FONT]
[FONT=&quot][/FONT]​
[FONT=&quot] “Thermal Effects on Connections for Floor Beams and Girders[/FONT]​
[FONT=&quot]Walk off occurred when beams that framed into the girders from one side thermally expanded and the resulting compressive forces in the beams pushed laterally on the girder from one side, sheared the bolts at the seated connection, and then continued to push the girder laterally until it walked off the bearing seat. A girder was considered to have lost vertical support when its web was no longer supported by the bearing seat. The bearing seat at Column 79 was 11 in. wide. Thus, when the girder end at Column 79 had been pushed laterally at least 5.5 in., it was no longer supported by the bearing seat.“[/FONT][FONT=&quot](p.527)[/FONT]
[FONT=&quot]
[/FONT]​
[FONT=&quot]The failure of the girder by buckling is clear. Is this second explanation consistent with the buckling mode?[/FONT]​
[FONT=&quot]a) [/FONT][FONT=&quot]The beams continued to push laterally in both explanations.[/FONT]​
[FONT=&quot]b) [/FONT][FONT=&quot]The girder lost vertical support when the web was no longer supported by the bearing seat in both explanations.[/FONT]​
[FONT=&quot]c) [/FONT][FONT=&quot]The girder end at Column 79 had been pushed laterally at least 5.5” (half the buckling flange failure lateral distance from vertical was 5.25”) in both explanations.[/FONT]​
[FONT=&quot]d) [/FONT][FONT=&quot]The girder was no longer supported by the bearing seat in both explanations.[/FONT]​
[FONT=&quot] [/FONT]
[FONT=&quot]
[/FONT]​
[FONT=&quot]5) [/FONT][FONT=&quot]NIST is right, fire not explosives caused the collapse of WTC7[/FONT]​
[FONT=&quot] [/FONT]​

[FONT=&quot][/FONT]​
[FONT=&quot] [/FONT]
figure827.jpg
​
 
gerrycan said:
Wouldn't the stress and strain that this girder is supposedly subjected to damage the end connections at all? After all, even though it is a shorter span, why wouldn't the same kind of forces that supposedly damaged the C79-44 girder connection at C79 100% horizontally, lead to similar damage at the ends of C79-80 ? Can you envisage a scenario where there would be no damage whatsoever at the ends?
Click to expand...

It's probably worth noting that they are completely different types of connection (a 5 bolt knife connection Vs a seated top clip connection with 4 bolts) which will react differently. The girder framing columns 76-79 used an 8 bolt knife connection.
 
Reactor drone said:
It's probably worth noting that they are completely different types of connection (a 5 bolt knife connection Vs a seated top clip connection with 4 bolts) which will react differently. The girder framing columns 76-79 used an 8 bolt knife connection.
Click to expand...


NIST had a lower failure threshold in knife connections compared to seated ones, so yes, it is critical that these connections are accurate in both models isn't it?
 
gerrycan said:
And did they release details of their "judgement calls" ? Do we have the chance to scrutinize these NIST estimates?
Click to expand...

Yes they did. Did you read the report?

Your problem is you are not looking at the whole picture. They did explain justifications and assumptions. You're looking at output only and not balancing it with the input justifications. This is why no engineers are paying attention to you guys.

Point blank but true. You need to show why their assumptions and justification are false, not the sym output.
 
Status
Not open for further replies.

Back
Top Bottom