Willis Tower, formerly christened ‘Sears Tower’ is a centre of business and the tallest skyscraper in Chicago, Illinois, United States. Chicago’s skyline owned Willis Tower as the world’s tallest building until the inauguration of the Burj Khalifa in Dubai, UAE. Currently it is on the second place among the world’s tallest buildings, is the tallest skyscraper in the western hemisphere and the tallest building in the United States.

Willis Tower has 108-storeys and stands at 1,450 feet (443 meters) - 1,730 feet (520 meters), which include the heights of twin antenna towers. The Tower offers 3.8 million square feet of space inside for retail and business purposes; and it cost more than $150 million to create this building.

Salient Features:

• The structure is formed from 9 bundled square tubes, each 75 feet wide with no columns between the core and perimeter. Two of the tubes are 50 floors high, two are 66 floors, three are 90, and two are 108.
• The construction with separate tubes provides lateral strengths to withstand the strong Chicago wind loads, as each tube only needs to take a part of the pressure.
• Facades consist of 28-acres of black anodized aluminium panels and approximately 16,100 bronze-tinted windows.
• Six roof-mounted robotic window washing machines are used to clean all 16,100 windows.
• The tower has a pressure lock at the freight entrance to combat the 'stack effect' generated by the differential in air pressure caused by cold air meeting warm air in the building.
• Includes world's fastest observatory elevators at 1600 feet per minute.
• Solar panels on the 90th floor roof of this tower are used to heat water for restrooms.
• Smart lighting systems installed here will automatically dim when enough sunlight is available inside.
• Includes 25,000 miles (40,223 kilometres) of electrical cable and approximately 43,000 miles (69,200 kilometres) of telephone cables.

Skydeck

 
The most attractive feature of the Willis Tower is the observation deck, or the “Skydeck”, which is 1,353 feet (412 meters) high above the ground. The Skydeck occupies the 103rd floor, the highest non-mechanical floor in the building. It has its own entrance on Jackson Boulevard, and attracts approximately 1.5 million visitors per year.

Skydeck offers the best views of Chicago and it is possible to see four states - Illinois, Indiana, Michigan and Wisconsin, as the range of view is 40 - 50 miles (65 - 80 kilometres) from here.

Another attraction at the Skydeck is 'the Ledge', a glass balcony extending 4.3 ft from where one can look straight down. The glass balcony is 10ft high and 10ft wide, and can hold five tons of weight with its 1.5 inches-thick glass. The transparent walls, floor and ceiling leave visitors with a feeling of floating in air.

Each glass box is comprised of three layers of glass laminated into one seamless unit. The low-iron, clear glass is fully tempered and heat-soaked for durability. In addition, the motorized system that projects and retracts the boxes from the building utilizes steel Linear Beams.

This Skydeck is cold, almost icy to the touch and gives a rather eerie feeling when looked at!