First of all, the core columns were mostly ‘braced’ by floor beams and slabs. These things provide only limited bending resistance compared to the deep spandrel plates of the exterior walls.
With that said, let’s demonstrate that the core could collapse without lateral bracing.
Consider a 40 storey, 480ft remnant whose base load is just 10% of normal at 1.8 to 2.1ksi. I don’t know the gyradius, but it’s probably in the range of 1-2ft. So let’s use this handy derivative of the self-buckling equation
Slenderness² × base strain = 7.8373
Slenderness = 361 to 335
So gyradius = 1.3 to 1.4ft
FOOTNOTES
1. Wikipedia gives self buckling equation
Length³ × density × gravity × area = 7.8373 × elastic modulus × area moment of inertia
Length × area = volume
Volume × density = mass
Area moment of inertia = gyradius² × area
Mass × gravity / area = base stress
Base stress) elastic modulus = base strain
Length / gyradius = slenderness
Therefore we get
Skenderness² × base strain = 7.8373
2.The core columns were mostly made of 36 and 42 ksi steel ... Read even more
