What structural system is associated with Chicago’s John Hancock Center?

Chicago’s John Hancock Center is associated with a trussed-tube structural system. The building, now officially called 875 North Michigan Avenue, uses visible diagonal braces to help resist wind and support its great height.

Designed by Skidmore, Owings & Merrill, the tower was completed in 1969. Its distinctive X-bracing is not merely decorative: the exterior structure helps the building act as a rigid tube against lateral forces.

The design was developed under structural engineer Fazlur Rahman Khan, whose innovations transformed tall-building construction. Trussed-tube systems use diagonal members around the perimeter, allowing the outside of a tower to contribute strongly to its structural performance.

The building is commonly called the John Hancock Center, even though its official name changed in 2018. It should not be confused with Chicago’s Willis Tower, another SOM project that is famous for its bundled-tube system.