The Sears Tower, over 1,700 ft high, overlooks the west side of Chicago's downtown Loop and is clad in bronze-tinted glass and stainless aluminum.
"Originally designed in the late 60's by Bruce Graham of Skidmore, Owings, and Merrill for Chicago-based Sears, Roebuck and Co, Sears Tower was topped out in May of 1973."
"The superstructure consists of nine interlocking tubes that terminate at different heights, creating the iconic stepped-back appearance of the tower. 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.
This "bundled-tube" configuration was a revolutionary engineering concept at the time, pioneered by SOM's very own Fazlur R. Khan. It allowed for large open office spaces on the lower levels, where Sears, Roebuck and Company would reside, and smaller floor plates on the upper levels with unobstructed views of the cityscape. To aid in occupant comfort, belt trusses were rigged on the upper mechanical floors thereby further reducing shear forces (i.e. wind-induced sway)."
As of July 2009 the building was renamed Willis Tower.