Architecture ,Engineering and Construction

• The superstructure consists of nine interlocking (square)tubes (Bundled tube system) that terminate at different heights, creating the iconic stepped-back appearance of the tower.The sides of the squares are 75 feet (for an overall width of 225 x 225 ft btw. exterior column lines and 229' at outside faces). Height to width ratio is 6.45:1
  
  
• This "bundled-tube" configuration was a revolutionary engineering concept at the time, pioneered by SOM's very own Fazlur R. Khan.

• Each tube is a rigid steel frame that performs in tandem with its neighbor to efficiently counteract all lateral and gravity loads. (This is in contrast to the popular tube-in-tube system, in which a rigid network of floor diaphrams and closely-spaced exterior columns work in unison to resist lateral loads whereas a centralized core functions to carry vertical loads exclusively.)

Click Here to view Bundled tube system and Here for Tube-in-Tube system

• It allowed for large open office spaces on the lower levels and smaller floor plates on the upper levels with unobstructed views of the cityscape.Sears, Roebuck and Company reside in the lower level .

• To aid in occupant comfort, belt trusses were rigged on the upper mechanical floors thereby further reducing shear forces (i.e. wind-induced sway).

• Building automation was a primary design consideration as well. For fire, security, and HVAC monitoring and control, engineers opted for a Honeywell computer system, one of the largest such networks ever installed at the time.

• Another technological innovation was the robotic window washers that could be programmed to descend along tracks built into the curtain wall. Currently, they operate eight times per year.

• Vertical transportation was also crucial. Designers had to ensure efficient flow of pedestrian traffic throughout the building — which, on any given day, could number in the tens of thousands. Westinghouse Electric Corp. employed "skylobbies" for this purpose, a system which Otis Elevator Co. Designated transfer-floors would be served by banks of double-deck express elevators. Separate banks of local-service elevators would carry passengers to their final destination.

Early stage of construction

Later stage of construction