'What about building 7'?

[DGM]

Not at all. I am questioning the validity of the connection failures around C79 that were carried into the LSDYNA model from ANSYS.

Based on what analysis?

 

[pgimeno]

The beam pushing due to thermal expansion was what NIST claim to have happened in their model.

Contact interaction between the end of the beam and the girder was modeled using a node-to-node contact element with an initial gap. When the connection was subjected to a large horizontal tension, a walk off failure occurred when the bolts sheared at the seat connection, the bolts sheared or the weld failed at the top clip angle, and the beam walked off the seat.

Why do you keep using the draft report? That paragraph is completely changed in the final report.

The entire section titled "Analytical Model for Seated Connection at Columns 79 and 81" is different in the final report. Here's what the paragraph equivalent to yours says:

A node-to-node contact element with an initial gap representing the clearance between the end of the beam and the column was used to model the contact between the beam and the column when the bolts sheared off and the beam moved enough to touch the surface of the column. The bolts could fail in shear under a tensile, compressive or lateral force, but the beam would only walk off the seat under a tensile or lateral force. The failure of the bolts and weld was a prerequisite for the beam end walking off the seat. The travel distance for walk off was 6.25 in. along the axis of the beam and 5.5 in. lateral to the beam. A walk off failure occurred when the bolts sheared at the seat connection, the bolts sheared or the weld failed at the top clip angle, and the beam walked off the seat. A control element was used to model beam walk-off in the axial direction. Beam walk off in the lateral direction was monitored during the analysis.​

It seems I was wrong, and COMBIN37 was only used for walk off in the axial direction, and that instead they monitored the walk off distance by some other means.

 

[Animal]

(COMBIN37) Can be switched on or off and varied in ANSYS. For example, in fig 11-14 it would be set to 4.5" to signify failure. NIST modelled column 79 to be the same as column 81, which had a seat plate that was 11" wide, and no stiffener plates. Their rationale for deeming an element to have failed due to walk off was that the girder web should no longer be supported directly below ie the girder had walked so that half of its width was no longer resting on the seat plate. In the case of an 11" seat plate this would be 5.5". Once the element was deemed to have failed it could be removed from the analysis.
When it was pointed out to NIST that the plate was actually 12" wide, they dutifully found a typo which transformed their original walk from 5.5" to 6.25". The problem is that the maximum expansion that could be experienced by any of the beams is less than 5.5" never mind 6.25".
The beam pushing due to thermal expansion was what NIST claim to have happened in their model.

Repeating the same fatal flaw as so many troofers in the past.......There was no need for a beam to expand 6.25" or even 5.5" inches for the end of the girder to move the same distance.

Going back to figure 11-16 you can see that NIST did not account for stiffener plates at either side of the girder web and these would have increased the required walk off distance closer to 9" in order to have deemed this element to have failed.

Only uninformed troofers believe this and keep quoting the same nonsense.
The stiffeners only keep the flange ends from bending, the do not change the center of mass.

A collapse has to start somewhere, and NIST chose girder walk off at column 79 as their initiating event. I cannot envisage how this would happen in the building itself, but for NIST to claim the failure to have happened in this manner in their model is just plain nonsense.
They made no account for the plates, and they did not model the connection correctly.

you still didn't mention which drawing the figure you posted was supposedly based on..

Troofer incredulity is not proof.
Time to run back to your handlers and try to get more answers for things you have no understanding of.

 

[gerrycan]

Why do you keep using the draft report? That paragraph is completely changed in the final report.

The entire section titled "Analytical Model for Seated Connection at Columns 79 and 81" is different in the final report. Here's what the paragraph equivalent to yours says:

A node-to-node contact element with an initial gap representing the clearance between the end of the beam and the column was used to model the contact between the beam and the column when the bolts sheared off and the beam moved enough to touch the surface of the column. The bolts could fail in shear under a tensile, compressive or lateral force, but the beam would only walk off the seat under a tensile or lateral force. The failure of the bolts and weld was a prerequisite for the beam end walking off the seat. The travel distance for walk off was 6.25 in. along the axis of the beam and 5.5 in. lateral to the beam. A walk off failure occurred when the bolts sheared at the seat connection, the bolts sheared or the weld failed at the top clip angle, and the beam walked off the seat. A control element was used to model beam walk-off in the axial direction. Beam walk off in the lateral direction was monitored during the analysis.​

It seems I was wrong, and COMBIN37 was only used for walk off in the axial direction, and that instead they monitored the walk off distance by some other means.

And that "other means" in this case was purely NISTs "judgement". And that judgement was to suppose that the girder had failed in ANSYS so that condition at the C79 connection was transposed over to the LSDYNA model.

 

[DGM]

And that "other means" in this case was purely NISTs "judgement". And that judgement was to suppose that the girder had failed in ANSYS so that condition at the C79 connection was transposed over to the LSDYNA model.

Do you have an alternative analysis that compares with the depth of the NIST? I'm all ears and eyes.

 

[pgimeno]

And that "other means" in this case was purely NISTs "judgement".

Another bare assertion. You can do better at convincing people if you provide evidence of your claims and address the rebuttals instead of sticking with your already rebutted arguments.

ANSYS provides positional information that could indeed be monitored. NIST say they did. You say they didn't and don't support your claim.

 

[LSSBB]

And that "other means" in this case was purely NISTs "judgement". And that judgement was to suppose that the girder had failed in ANSYS so that condition at the C79 connection was transposed over to the LSDYNA model.

Seeing something fail in a simulation is purely a matter of judgement?

 

[gerrycan]

Are you questioning that the COMBIN37 element at the connection of A2001-C79 showed walk-off in ANSYS?

In the way that you suppose it did, yes.

Are you questioning the parameters that NIST fed to COMBIN37?

Yes

They claim that the analysis showed that the girder walked off; that was necessarily detected by COMBIN37.

Have you actually looked at what they are actually saying????

They attributed it to the expansion of the beams as the major factor. But (1) leveraging allows for the displacement at the seat to be greater than the expansion of the beams, and (2) the column displaced to the east, increasing the relative distance between the girder and the seat, possibly by several inches.

You think so?? Why do the figures that you posted earlier in this thread show no connection damage on the south and west connections at C79 then? Even in NISTs own words connection damage to the point of failure is a prerequisite to "walk" and obviously so.
If C79 had moved by expansion of the beam to the west of it, there would be significant connection damage along the span of that beam, in your earlier figure.

 

[carlitos]

Girders are primary and beams are secondary elements. .

 

[pgimeno]

Have you actually looked at what they are actually saying????

I made a correction. Something you should try from time to time.

If C79 had moved by expansion of the beam to the west of it, there would be significant connection damage along the span of that beam, in your earlier figure.

Are you saying that NIST lied when they said this?

On Floors 10, 11, and 12, tensile failure of knife connections occurred in the girder between Columns 76 and 79. The temperature of the girder between Columns 76 and 79 on Floor 13 was sufficient to displace Column 76 to the west and Column 79 to the east. The forced displacements at Floors 10, 11, and 12 created a tensile load in the girder knife connections to the columns, and failed the connection fillet weld to the column.
​

(NCSTAR 1-9 p.527)

 

[LSSBB]

You think so?? Why do the figures that you posted earlier in this thread show no connection damage on the south and west connections at C79 then? Even in NISTs own words connection damage to the point of failure is a prerequisite to "walk" and obviously so.
If C79 had moved by expansion of the beam to the west of it, there would be significant connection damage along the span of that beam, in your earlier figure.

What color is the dot at the other end of the beam?

 

[gerrycan]

Girders are primary and beams are secondary elements.

Steel Structures Third Edition - Page 109.
I did say that i was simplifying it, the above book puts it better. You should read it sometime.

 

[gerrycan]

What color is the dot at the other end of the beam?

It is white,on both showing "no connection damage" vertically or horizontally.
Are you looking at the right beam?

 

[gerrycan]

I made a correction. Something you should try from time to time.



Are you saying that NIST lied when they said this?

On Floors 10, 11, and 12, tensile failure of knife connections occurred in the girder between Columns 76 and 79. The temperature of the girder between Columns 76 and 79 on Floor 13 was sufficient to displace Column 76 to the west and Column 79 to the east. The forced displacements at Floors 10, 11, and 12 created a tensile load in the girder knife connections to the columns, and failed the connection fillet weld to the column.
​

(NCSTAR 1-9 p.527)

And here is the analysis to which your quote refers.
The ANSYS model doesn't support the above statement at all, and neither do the figures that you posted. You should by now realise that this was a "judgement" call by NIST.
Here it is at 3.5 hours - no failure in that beam. Look at it for the other times, you will not find that the beam has failed in any of the ANSYS analytics.

Right up to 4 hours, when girders and beams are supposedly failing all over the place, still there is no failure in that beam. How can it therefore push the columns apart without expanding enough to damage the connections???
THERE IS NO BUCKLING OR END CONNECTION IN THE BEAM.

 

[gerrycan]

And that "other means" in this case was purely NISTs "judgement".

Another bare assertion. You can do better at convincing people if you provide evidence of your claims and address the rebuttals instead of sticking with your already rebutted arguments.

As noted previously, the ANSYS analysis used a non-linear static procedure with an implicit solution algorithm that solved for equilibrium at each time step, but did not account for the dynamic effects of
falling debris from framing failures in the floor systems. Based on preliminary analyses in LS-DYNA, which included the effects of dynamics caused bydebris impact from failed floor sections and engineering judgment, the level of failures, damage, and thermal weakening in ANSYS at 4.0 h was identified as likely to result in an initiating event in an LS-DYNA analysis

NIST got it horribly wrong.
Look at their LSDYNA modelling of the connection. It is not even the correct type of connection.

 

[DGM]

NIST got it horribly wrong.
Look at their LSDYNA modelling of the connection. It is not even the correct type of connection.

When will your counter analysis be ready for review?

 

[gerrycan]

When will your counter analysis be ready for review?

What about if I said it would take around 8 years, I wouldn't give you any structural drawings in order to review it, I won't give you the input data for any modelling etc etc
Also, you will only have 2 weeks to submit any comments.

Does that sound ok?

Oh.... and you can pay for it.

 

[LSSBB]

It is white,on both showing "no connection damage" vertically or horizontally.
Are you looking at the right beam?

Are you looking at a beam or a girder? I am speaking of the first beam to the west of C79.

 

[DGM]

What about if I said it would take around 8 years, I wouldn't give you any structural drawings in order to review it, I won't give you the input data for any modelling etc etc
Also, you will only have 2 weeks to submit any comments.

Does that sound ok?

Oh.... and you can pay for it.

I'd find this odd because you already claim they got it wrong. What analysis have you done to determine this? Can we see the qualifications of the engineers that did the study?

Are you asking me to pay for something I didn't ask for and you've already done?

 

[gerrycan]

Are you looking at a beam or a girder? I am speaking of the first beam to the west of C79.

C76 - 79 girder.