What's the difference? Those plates welded to the girder. They are called stiffeners. Why aren’t the stiffeners shown in the version above from the NIST report when they are shown in the actual WTC7 drawings? Why the stiffeners are so important: Stiffener plates are critically important. They allow a girder to transfer loads to a wider footprint (bearing surface) and increase its ability to resist failure. The stiffeners not only allow the load to be spread wider, but if the girder could shift (walk-off) as NIST alleges, they strengthen the web and bottom flanges. So if the girder web could somehow reach the edge of the 12” seat, the flanges would not fold under an offset load. NIST claims only 5.5” was necessary. They later revised this to 6.25”, but with the stiffeners the distance required would be approximately 10” before the girder could leave the seat. The stiffeners would make the type of failure that NIST supposed in their thermal expansion hypothesis completely impossible because the beams could not expand more than 4.75" no matter how hot they got. The reason the expansion is limited is because at just above 600C the beams shorten due to sagging more than they expand. The stiffener plates as shown in the WTC7 drawings were installed on the key girder that NIST claims initiated an unprecedented global progressive collapse of the building. NIST did not include them in their analysis. Thus if the girder can’t walk-off the seat it does not fall onto floor 12 and likewise floor 12 doesn’t collapse. The whole progressive collapse scenario evaporates without an initiating event. The stiffeners are the Achilles Heel of the NIST conclusion. They are truly the “game changers” described by mechanical engineer Tony Szamboti. Many other engineers agree. This walk-off is a pure, unadulterated fantasy.