Architecture, Engineering and Construction
The Willis Tower is an “international style” design
consisting of square tubes in a 3 by 3 tube arrangement,
with each tube having a footprint of 75 by 75 ft., in
essence creating a unified bundle of nine tubes. The
Willis Tower was the first building for which this type of
“bundled-tubular” construction was used. This design
provides stability against high winds and also allows
for future upward growth if so desired by the owner.
The 222,500-ton or 445 million pound building is
supported by 114 rock caissons secured into bedrock.
The foundation and the floor slabs combine to equal 2
million cubic feet of concrete. 76,000 tons of
prefabricated steel frame sections measuring 15 x 25
ft. were put in place. The Willis Tower has more than
16,000 bronze-tinted windows and 28 acres of black
aluminum cladding or “skin”.
As the building climbs upward, the tubes begin to
drop off giving the Willis Tower its characteristic
setback or “step-back”. This geometry of the 110-story
tower was developed in response to the original
interior space requirements of Willis, Roebuck &
Company. The configuration incorporates the
unusually large office floors necessary to Willis’
operation along with a variety of smaller floors.
A revolutionary vertical transportation system was
instrumental in the Willis Tower reach in soaring to
new heights never previously achieved. 16 Double-
decker express elevators travel from the first two
floors to “sky-lobbies” located at floors 33/34 and
66/67, where passengers transfer to single local
elevators serving all other individual floors. Among the
world’s fastest the elevators servicing the observatory
travel at 1,600 ft. per minute.
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