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(now Willis Tower)
AR – 412
Design of Multi-storeyed Buildings
• Location: Chicago, Illinois
• Project Completion: 1974
• Site Area: 3 acres
• Project Area: 4,565,844 ft2 (105 acres)
• Number of Stories: 110
• Building Height: 1,450 ft (442 m)
• Market: Commercial + Office
• 3.8 million rentable square feet (89 acres)
• 159,000 square feet of retail space. (0.36 acres)
• 160-car executive parking garage.
second-tallest building in the United States
While 12th-tallest in the world
25,000 daily visitors12,000 occupants
Forces and Form
• The Willis Tower draws its strength, both visual and physical, from its structural
form, the bundled tube.
• The building plan consists of 9 squares, each 75 feet across, placed in a three-
by-three grid arrangement.
• Each square has 5 columns per side spaced 15 feet on centers, with adjacent
squares sharing columns.
• As the columns rise up the building, each square in the plan forms a tube,
which can be seen on the exterior of the building.
• These tubes are independently strong but are further strengthened by the
interactions between each other through truss connections.
• While the tubes connect at each floor level with beams and floors trusses,
several large trussed levels act as the main horizontal connectors in the
• These trussed levels, which also contain the mechanical systems for the
building, appear as black horizontal bands on the façade. While the louvres
covering the trussed levels mask the structural details, the purpose of these
levels remains abundantly clear visually.
• The closely spaced interior and exterior columns are tied at each floor with deep spandrel beams.
At the truss levels, these tubes are tied together.
• These ties resulted in a stiffer structure, as the building acts as a unified system of stiffened
• The interaction between the individual tubes and the belt trusses at mechanical levels allows the
building to attain its extreme height.
• Due to the drop offs, the gravity loading on the system is not evenly distributed along the height
of the building.
• These trusses take the gravity loads from above and redistribute them evenly onto the tubes
• This is particularly important for the uppermost section of the tower, due to its asymmetry about
the central axis of the building.
• The presence of the belt trusses help to mitigate these effects of differential settlement, which
cause the building to tilt.
Spandrel beams are load-bearing structural members around the perimeter of a floor of a building. Not only may they support loads from the roof and other floors, they may also help support a
building's walls. For example, walls expected to experience significant forces from wind may be anchored to these beams to better distribute the load.
X bracing of the columns at the mechanical
29th – 32nd
64th – 65th
88th – 89th
104th – 108th
• The Sears Tower’s 104-cab elevator system divides the building into three separate zones, with
sky lobbies in between at levels 33-34 and 66-67.
• 28 double decker express shuttle shuttle elevators serve the sky lobbies
• 63 single deck elevators for intra-zonal travel
• 6 freight elevators
• Two express elevators that take 61 seconds to reach the 1353 foot high skydeck at level 103
travelling at 1600 feet per minute.
1,730 feet (527.3 m)
1,450 feet (442.1 m)
1,353 feet (412 m)
• The exterior skin of the building is an expression of the structural
skeleton inside, with the fire proof frame sheathed in black
aluminium and glare reducing bronze tinted glass.
• The exterior skin is maintained with yearly check ups and six window
Willis Tower has a footprint that encompasses an entire square city block. It’s even its own
zip code. Truly a city-within-a-city, you might be surprised to learn some of these stats
about the building:
• Willis Tower features 16,100 windows and six roof-mounted robotic window washing
machines clean them.
• Willis Tower’s square footage is the equivalent of 101 football fields.
• It took 2,000 workers three years to build the tower.
• Approximately 43,000 miles (69,200 kilometers) of telephone cable runs through the
building - enough to stretch across the continental United States 15 times.
• Willis Tower weighs 222,000 tons.
• The average sway of the building is approximately six inches (152 millimeters) from true
center, but the building is designed to sway up to three feet.
• Willis Tower elevators operate as fast as 1,600 feet (488 meters) per minute - among the
fastest in the world.
• Each working day, between 15,000 and 20,000 people come and go from Willis Tower
• Skydeck Chicago debuted The Ledge in 2009, unveiling a breathtaking view
of the city, 1,353 feet straight down to Wacker Drive and the Chicago River.
Since then, it has become a “must-do” Chicago experience for locals and
• The Ledge features glass panels that are 1 ½ inches thick and can hold 5
• The Ledge’s glass boxes are designed to retract into the building, allowing
easy access for cleaning and maintenance.
• Approximately 1.4 million people visit Skydeck each year, a 30% increase in
attendance since the debut of The Ledge.
• On a clear day, you can see four states from Skydeck on the 103rd floor:
Illinois, Indiana, Wisconsin and Michigan. Visibility from the Skydeck is
approximately 40-50 miles (65 - 80 kilometers).