the Citicorp thing is one of the great stories of modern architecture. It was a student who discovered the flaw and brought it to the attention of his prof. who brought it to the attention of the developers. They fixed the flaw after the building was built and occupied by, in part, installing a giant concrete counter-weight that slides back and forth on rollers near the top of the building.
Yeah, that was it. I didn't recall it was discovered after the building started getting tenants. I should track that docu down again - amazing stuff, huh?