A 2,000 km rotor at 14 km/s supports the elevated track — but the equilibrium is unstable, like balancing a ruler on end, all along its length. There's no material stiffness holding it up; only active stabilization. Turn it off, or push the rotor past the control margin, and watch it buckle.
Two destabilizers, both modeled: the maglev gap holding track to rotor is Earnshaw-unstable at every point, and the rotor's momentum flux acts on curvature — the fluid-conveying-pipe flutter term, v²·y″. Bending stiffness picks the buckle wavelength.
Stabilization must out-muscle both the gap instability and the flutter term. Push the rotor up and the margin shrinks; past ~1.5× nominal in this model, even active control loses and the loop buckles at its preferred wavelength. It's not unconditional.
Ordinary steel — no exotic strength anywhere. What replaces material stiffness is thousands of fast control nodes damping the whole moving mass in real time. The building is, physically, a distributed controller.