Sears Tower: a Technological Marvel of the 20th Century
Plan Plus Volume 1 No 1 2002 (1-5)
SEARS TOWER: A TECHNOLOGICAL MARVEL OF THE 20TH CENTURY
Dr. M. A. Muktadir
Professor of Architecture
Ahsanullah University of Science & Technology, Dhaka
Abstract
This paper briefly describes the key features of Sears Tower, a technological marvel of the 20th century. The
110 storied Sears Tower is an engineering wonder of the world. Sears Tower is 204 feet taller than the
Empire State Building but weighs far less than 223,000 tons. 42-inch deep steel beams at each floor level
brace the columns of this huge structure. The major “plant floors” contain electrical sub-stations, water and
air-handling machinery and elevator hoist motors. There are 28 double–decker elevators travelling at 1600
fpm, for the users of floors above the 34th floor. Since each bank of single-decker elevators only serves a
small group of floors, people can change between local elevators in transfer floors at levels 10, 17, 23, 42 and
49.
Key words: Form, Structure, Bundle-tube, and Function.
Introduction
Sears tower is located in Chicago, Illinois, in the United States. This mega-project was completed
in 1974. The chief designer is Dr. Fazlur Rahman Khan of Skidmore Owings and Merrill (SOM).
This 110 storied tower is 1450 feet high. The area of this tower block is 3.7 million square feet and
steel is the structural material. Sears Tower has an outer covering of black duranodic aluminum.
This tower is used as an office complex. Sears Tower is 204 feet taller than the Empire State
Building but weighs far less than 223,000 tons (Beedle, 1983).
Form and Structure
Sears Tower is one of the most innovative mega-structure of all times. ‘Form Follows Function’ is
perhaps the best way to describe the Sears Tower. The form is generated by the revolutionary
‘bundle-tube’ concept. There are nine bundled tubes, which constitute the structural frame of the
building. All nine tubes rise together for the first 49 floors where two of the corner tubes
terminate. The remaining seven climb to the 65th floor where the other two corner tubes stop. The
remaining five sections rise with a cruciform plan to the 89th floor. A small penthouse on the roof
accommodates the cooling towers and the uppermost wash robots (Beedle, 1995).
1
Plan Plus Volume 1 No 1 2002 (1-5)
The outside of each tube is made-up of 16 nos. of 40-inched
wide minor steel columns with their centers 15 feet apart.
There are also bigger major columns, totaling 16, on the
corners of each tube. 42-inch deep steel beams at each floor
level brace the columns. With the entire supporting steel
outside, the interior of each tube, measuring 75 feet by 75
feet, is free of columns. Each level is bridged by a series of
3-foot deep trusses or floor beams, which support the metal
deck onto which the concrete floor is poured. The utility
spaces and banks of elevators are all clustered around the
center of each floor leaving the more desirable window
areas free for offices. A curtain wall of 16,100 bronzetinted reflective windows and black duranodic aluminum
panels encloses the whole building (Hall, 1995).
Foundations
The columns of each tube continue down to the lower level
3. Here they are connected to a 7-feet diameter and 60-feet
deep concrete bedrock cassions which are the cylindrical
foundation supports set into the limestone bedrock to
anchor the whole structure (Banavalkar, 1995). These
bedrock cassions exist only under the tower where they are
necessary and the rest of the site is supported by 3-foot
diameter hardpan cassions, which extend just 22 feet into
A Panoramic View of Sears Tower
the clay hardpan. The foundations are all connected to a
massive concrete raft, which also forms the lowest basement floor. This raft, together with a 30inch wide concrete diaphragm wall all around, forms a barrier against the underground water and
keeps the site dry (Hall, 1995).
Environmental Control
Sears Tower is a huge airtight container sealed from the outside by a glass and aluminum skin. It
maintains its own comfortable thermal environment inside by means of an air-handling system,
which consists of a network of aluminum ducts running in the ceiling spaces. These ducts act like
arteries and veins transporting freshly filtered air of right temperature and humidity around the
building and removing stale air.
During the daytime, heat builds up within the building from the sun streaming in through the
windows, from the body heat of thousands of people working and circulating within the building
and also from the innumerable computers, photo-copiers and other equipment which form an
2
Sears Tower: a Technological Marvel of the 20th Century
essential part of the life in the tower. Any change in air-temperature is picked up by electronic
Structure of Sears Tower
sensors and relayed to the command center. There the
duty engineers can adjust the output of the chillers and
control the quality and amount of airflow around the
building.
Most of the machinery that keeps the tower running
smoothly is housed at the ‘plant floors’ located at 5
points up the building on lower levels 2-3, and levels
29-32, 64-65, 88-89 and 104-109, yet each floor has
some local plant such as air-handling boosters. The
major plant floors contain electrical sub-stations, water
and air-handling machinery and elevator hoist motors.
The 29th floor is home to the chillers that control the
temperature of the air that is pumped around the
building. There are five chillers, which are effectively
huge refrigerators for cooling water. Air is pushed
through the water to chill it and then pumped to the
five plant zones (level 23, 29-32, 64-65, 88-89 and
Plan and shape of Sears Tower
104-109). From there, it goes to the individual floors. The chillers are monitored on computer
screens in the chiller plant room (level 29) and the command center.
3
Plan Plus Volume 1 No 1 2002 (1-5)
Elevator System
There are 104 elevators in Sears Tower: 8 are for freight, 2 serve the sky deck at level 103, and the
rest 94 are for tenants. There are 28 double–decker elevators travelling at 1600 fpm, for the users
of floors above the 34th floor. These elevators whisk people nonstop from the concourse level
straight up to the sky lobbies at levels 33-34 and 66-67. These sky lobbies are two-story
interchange points with escalators to connect the two floors. They give access to the single-decker
elevators, of which there are 66 that take people to individual floors.
There are three groups of floors served by single-decker elevators. These are:
(i)
(ii)
(iii)
Level 1 to 28
Level 33 to 68
Level 66 to 102
Since each bank of single-decker elevators only serves a small group of floors, people can change
between local elevators at transfer floors at levels 10, 17, 23, 42 and 49.
When the wind speed exceeds 40 mph, anemometers on the roof detect it and alarm bells start
ringing in the command center. Problems only occur when the wind speed rises to a speed of 60
mph. Although this only makes the top of the building sway by less than a foot which is barely
perceptible inside the tower, even such a small movement could be enough to jam the sky deck
and freight elevators, those with the longest cables suspended from cable drums on the 106th floor.
To avoid any problem, the speed of these elevators is reduced, to correct any sway, they are
stopped for a moment at every 10th floor. Since the local elevators cover only relatively short
distances, their operating speeds are just reduced.
Maintenance
For inspection of the building’s 76000-ton steel frame, the sealing around the windows and the
integrity of the plastic film over the glass, a man in white overalls is suspended in a cradle from
the 109th floor. Every year, the entire curtain wall is thoroughly checked. The inspection is part of
a systematic maintenance program, rigorously followed to mend and replace components before
they fail. Remodeling and refurbishing office space is carried out throughout the day and night.
New partitions, ceilings and light fixtures are installed and the space is decorated in the contours,
and finishes chosen by the new tenant.
Six wash robots clean the outside of the building eight times a year. The washing component is
lowered down the building on cables at a rate of 45 fpm. It squirts surd-free detergent onto the
windows and then brushes, rinses and vacuums it off all in one movement. The dirty water is then
filtered by the unit and reused.
4
Sears Tower: a Technological Marvel of the 20th Century
Concluding Remarks
Much time has elapsed since the construction of the Sear’s tower. It is no longer the tallest
building on earth. The Petronas tower of Malaysia has now emerged as the tallest structure of this
planet in the new millennium. Many more tall buildings will be built very soon in different parts
of the world, some of which might surpass the Petronas tower too. The engineering and
architectural world knew Dr. Fazlur Rahman Khan as the designer of the Sear’s tower, the then
world’s tallest building. He is also the designer of the John Hancock Center in Chicago, one time
the world’s tallest multi-use building. Dr. Khan was an innovator of structural form of tall
buildings and a master at the art of blending the practical with the functional and aesthetic. He
developed the concept of tube in tube structure for the design of tall buildings, which was
extensively used for several tall structures. Fazlur Rahman Khan was the major moving force for
the council of tall buildings. Dr. Khan died on March 27, 1982 while on a business trip in Jeddah,
Saudi Arabia. His death was a great blow to the world’s community of people involved with tall
buildings. The loss of Dr. Fazlur Rahman Khan to the engineering and architectural profession is
irreplaceable.
References
Banavalkar, P. V. 1995. “Concept and application of spine structure for high rise buildings”, in Beedle, L. S.
Ed. 1995. Habitat and the high rise tradition and innovation, Council on tall buildings and urban
habitat, Dutch council on tall buildings.
Beedle, L. S. (ed) 1983. Developments in tall buildings, 1983, Council on tall buildings and urban habitat,
Van Nostrand Reinhold Company, New York.
Beedle, L. S. (ed) 1995. Habitat and the high rise tradition and innovation, Council on tall buildings and
urban habitat, Dutch council on tall buildings.
Hall, L. 1995. “Composite and steel high rise systems” in Beedle, L. S. Ed. (1995) Habitat and the high rise
tradition and innovation, Council on tall buildings and urban habitat, Dutch council on tall
buildings.
5