The 9/11 Forum

T-Smaboti Quote: The girder would fall from the bearing seat before it reached the very edge of the flange, even with the stiffeners, as at some point there wouldn't be enough bearing surface. I would estimate that with about 2 to 2.5 inches of flange still on the bearing seat the girder would fall...

You will see in NCSTAR, Vol.1, Page 558, PDF page 220 that NIST adds a vertical stiffener plate to their global model. This is an error. Did they include this is the analyses? We are trying to find out just exactly what they did include. http://img820.imageshack.us/img820/4731/ncstar19vol2pdf220sea...

Quote T_Szamboti: The real dimensions for the girder to walk-off the bearing seat are 6.25" axially and 6.29" laterally. However, in the axial direction the girder would fall after the stiffeners were no longer over the 2" thick x 14" deep support plate below the bearing seat, m...

The distance from the flange tip to the far side of the web was actually half the width of the 11.51" wide flange = 5.75" + half the thickness of the 0.58" thick web = 0.29" for a total of 5.75" + 0.29" = 6.04". The distance they actually mean is half the width of ...

dynamic = moving static = still It is actually a little more involved than that. The term dynamic load often is what is used to describe an impulsive load, where the load is due to an impulse and amplified above that of the static load. The amplification comes from the additional acceleration of th...

Enik, I've looked at your 3D visualizations again and again, but I don't see the same physical constraint (the "socket") for the girder in there as I see in the photos. What gives? In the picture the girder end appears completely encapsulated, while in your simulation, fixed or not, it se...

Thanks Tony... and that was the point of my question. Why focus so much on the walk off when the results of the walk off can't alone lead to any sort of global collapse.' It seems like a distraction to be arguing over this point when it's really immaterial to showing the NIST explanation is nonsens...

Assuming the girder could and did walk off the seat... How would that lead to the collapse of the building? It would have removed the north side girder lateral support from column 79. However, that in and of itself would not be enough, as the column only needs support from two orthogonal directions...

I did a finite element model of the five beams and girder myself today using a delta T of 70 to 1,112 degrees F ( 600 degrees C) and the midpoint CTE of 7.01 x 10e-6 in/in/deg F of the midpoint temperature in that range of 591 degrees F. I let the column 44 side rotate but not translate, as though i...

To be clear on the interaction point, Imagine that there were only one beam in the middle pushing on the girder. Let's say this beam is 22.5 feet away from both column 44 and column 79 and the column 44 side is a pivot. Now when this beam pushes the girder 4.5 inches at its middle position on the gi...

Enik, It is hard to imagine that an interaction between the beams and the girder could cause extra movement of the girder if the beams have a hard connection to the girder. Is the connection between the end of each beam and the girder a hard connection in your model? The girder will bow some from th...

I believe that NIST decided for some unstated reason NOT to examine anything below floor 8 in B7... as if it wasn't there... that everything down there was 100% normal and did not require any examination or discussion. My hunch is that they were avoiding the areas where the story was... perhaps on ...

How do you know there were no fires on 5&6 floors? I am speaking of the vicinity of column 79. NIST does not claim there were fires on floors 5 and 6 in the northeast of the building, as they have no evidence for it. They do discuss some hypothetical scenarios concerning diesel tanks on these f...

Wouldn’t it be more prudent to start working on the NIST theory of the buckling of column 79 due to the loss of lateral load from multiple floors? There is work being done on the column 79 issue. A very conservative analysis of that column, per the 13th edition of the AISC Manual for Steel Construc...

Here is my take regarding the modulus of Elasticity and COE between the NIST and ASTM A572. Whether the NIST was right or wrong, the NIST created a scenario, modeled it, and I was able to recreate it. I think we might be splitting hairs on the input data but everything I have entered shows the web ...