The Onterie Center is a sixty-story award-winning high rise in downtown Chicago, IL. It is located at 441 East Erie St, and takes its name from a conflation of "Ontario" and "Erie", the streets at its two entrances. Designed by Skidmore, Owings & Merrill, construction was completed in 1986. The building is two towers: a 60-story Main Tower and an 11-story Auxiliary Tower. The diagonal brace structure is dedicated to respected structural engineer and designer Fazlur Khan, and serves as an architectural nod to Khan's John Hancock Center. The X formations on the exterior are concrete infill panels which act together to form a truss tube. There are no steel beams behind them.  Onterie Center is the first concrete high-rise in the world to use diagonal shearwalls at the building perimeter. This type of design uses fewer columns and allows for a distinct unit layout. (wikipedia.org)