Conversation so far:
What was the tube structural system?
His "tube concept", using all the exterior wall perimeter structure of a building to simulate a thin-walled tube, revolutionized tall building design.
Did this system do well?
Most buildings over 40 stories constructed since the 1960s now use a tube design derived from Khan's structural engineering principles.

Question: Was this system used for anything else?
Self-contained rewrite: Was  the tube structural system used for anything else besides simulation of  a thin-walled tube?