1965: John Hancock Center – Chicago, Illnois
Innovation: John Hancock Center
Location: Chicago, Illnois
By: Skidmore, Owings, and Merrill
The John Hancock Center, a 100 story structural expressionist skyscraper by Skidmore, Owings, and Merrill was one of structural engineer Fazlur Khan’s first buildings to exhibit much of the structural systems found in many of today’s modern skyscrapers.  Khan’s understanding of structural systems would allow engineers to create buildings that reached heights few could dream of. During the time of the construction of the John Hancock Center, 20 story buildings were still noteworthy, but Khan’s Tube Structural Systems would allow buildings to reduce the lateral loads such as wind and seismic forces that kept buildings low to the ground, while significantly reducing the amount of steel needed per square foot. His system accomplished this by utilizing the exterior wall perimeter of the structure as thin walled tube. Khan’s X-bracing added to the structural integrity by directing forces to the exterior columns, eliminating the need for interior columns. 
The John Hancock Center not only gave engineers the tools to create modern skyscrapers, which rely on their ultra light weight design to allow them to top out at incredible heights, but also stands as a terrific example of structural systems presented in an exterior aesthetic form. Other later buildings such as the Llyod’s Building do this quite well.