The builders added far more steel reinforcement than FLW called for... because it was blindingly obvious that it would collapse under its own weight rapidly by his design.
Even with this steel added behind the architects back its still suffering cracks and damage due to being underengineered.
Its a beautiful property, but he grossly underengineered it. He was driven completely by estetics.
He must have learned his lesson. The Johnson Wax Headquarters is over-engineered. When they tested the tulip-shaped supports, they held something like twice the weight required.