Sears Tower(now Willis Tower)

AR – 412Design of Multi-storeyed Buildings

Neelesh Sharma

[11110034]

Sears Tower• 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 world25,000 daily visitors12,000 occupants

SITE PLAN

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 buildings. • 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 tubes.

• 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 below.

• 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.

Interior Beams and Columns

Construction

X bracing of the columns at the mechanical floors

29th – 32nd

64th – 65th 88th – 89th 104th – 108th

Vertical Circulation• 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)

38th Floor Plan

48th Floor Plan

85th Floor Plan

95th Floor Plan

• 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

washing machines.

The Ledge at Skydeck Chicago

FactsWillis 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

Most interesting• 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 visitors alike. • The Ledge features glass panels that are 1 ½ inches thick and can hold 5 tons. • 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).