Yes in either instance the building would probably be vulnerable to collapse because the buckling of the lower portion of columns in WTC 7 would result in the lower mass of WTC 7 not being able to support the upper mass of WTC 7 (as I think @Mick West explained in the first post in this thread).We're missing the point. The point was the loss of north-south restraint.
If the only damage on the tower was a complete removal of the wind girders of the east or west walls, the building would still have been destroyed. Because of wall crippling.
However, as was discussed a few pages back in this thread, regarding the amount of crumpling of the exterior curtain wall as it fell, I would think that for a collapse where the core failed independent of floor failures, the collapse might be more likely to be visually characterized by global failure of the outer perimeter shell falling down without significant crumpling (e.g. like in the BBC and CNN footage). Whereas in your example of partial removal of the wind girders of the east or west walls, I would think that the building collapse might be more characterized by inwards crumpling of the outer perimeter shell as it collapses (similar to what was seen in the NIST simulations, even though the NIST simulations aren't meant to be an accurate geometric representation of the collapse given the predicted pattern of structural failure that did take place).
However, the Q&A section on the NIST website regarding WTC 7 https://www.nist.gov/pao/questions-and-answers-about-nist-wtc-7-investigation
says this (italics emphasis mine)
Some people have said that a failure at one column should not have produced a symmetrical fall like this one. What's your answer to those assertions?
WTC 7's collapse, viewed from the exterior (most videos were taken from the north), did appear to fall almost uniformly as a single unit. This occurred because the interior failures that took place did not cause the exterior framing to fail until the final stages of the building collapse. The interior floor framing and columns collapsed downward and pulled away from the exterior frame. There were clues that internal damage was taking place, prior to the downward movement of the exterior frame, such as when the east penthouse fell downward into the building and windows broke out on the north face at the ends of the building core. The symmetric appearance of the downward fall of the WTC 7 was primarily due to the greater stiffness and strength of its exterior frame relative to the interior framing.
So possibly in any structural failure situation leading to collapse where the interior failures occurred before the exterior failures, the exterior frame of WTC 7 would appear to fall as one unit.
Yes, from your calculations it doesn't seem like it would have taken much stress nor required failure of a significant portion of columns in the building for the building to completely collapse. It seems that might be because of how the truss and column system was configured in the building design, which did not lend itself well to resisting collapse once failure of structural members had initiated, similar to how such a structure designed like WTC 7 was also more vulnerable to fire than conventional structures (which I think the NIST Q&A on WTC 7 had also mentioned):In fact, a partial removal would have been fine. For Euler buckling of the affected columns
Length² × strain = π² × gyradius.
At a rather low stress of 50MPa and with a gyradius of 7 inches or less consistent with the W14 section columns, the critical length would be 35m, or 10 storeys. This is for a fixed-guided boundary condition, which is applicable here as the the undamaged top block of the tower slides in the danaged section without rotating.
Why did WTC 7 collapse, while no other known building in history has collapsed due to fires alone?
Factors contributing to WTC 7's collapse included: the thermal expansion of building elements such as floor beams and girders, which occurred at temperatures hundreds of degrees below those typically considered in current practice for fire-resistance ratings; significant magnification of thermal expansion effects due to the long-span floors in the building; connections between structural elements that were designed to resist the vertical forces of gravity, not the thermally induced horizontal or lateral loads; and an overall structural system not designed to prevent fire-induced progressive collapse.
Does this mean there are hundreds or thousands of unsafe tall buildings with long span supports that must be retrofitted in some way? How would you retrofit a building to prevent this problem?Of particular concern are the effects of thermal expansion in buildings with one or more of the following characteristics: long-span floor systems, connections that cannot accommodate thermal effects, floor framing that induces asymmetric forces on girders, and composite floor systems, whose shear studs could fail due to differential thermal expansion (i.e., heat-induced expansion of material at different rates). Engineers should be able to design cost-effective fixes to address any areas of concern identified by such evaluations.