Sears Tower Chicago also known as Willis Tower Chicago marked ”skyscrapers era” in USA and for 20 years it was the tallest building in the world. It is 443 metres high, with 110 floors ground floor, and it is located in the centre of Chicago, Illinois, USA. That tower was built in 1973 for Sears, Roebuck and Company, a company with 7 000 employees so that all of them could fit under one roof.
The Sears Tower Chicago is first skyscraper made with brand new technology, at that time, and much taller than the other buildings. Because of its height, that skyscraper must be flexible in strong winds yet rigid enough to prevent large sideways movement.
Design
Ground floor of Sears Tower Chicago is made of 9 square pipes with side 22,9 metres long and different heights. Two of them are reaching the 50th floor, two reaching 66th, three 90th and the last ones are going all the way to the top. That solution makes the building visually thinner and more elegant. Even the floors have areas between 3 800 and 1 100 m2.
Construction
In every square there are 4,6 metres spaced steel columns. Columns and beams were made out of steel tin welded in W profile. Thickness is 100 mm in the bottom, where the load is the biggest, an only 25 mm at the top. Steel construction was made on concrete slab 1,5 m thick and the pylons. Pylons are concrete with steel reinforcement. Their diameter is 2,2 – 3 metres and they are 20 metres deep in the ground. Steel skeleton is prefabricated in dimensions 7,6 x 4,6 metres.
Elevators
Sears Tower Chicago has 102 elevators for employees, vertically it’s divided in 3 parts with 30 or 40 floors. In every part, at the bottom, there is ”sky lobby”. About 16 500 people can come to sky lobby with 14 fast elevators, and then there are local elevators which are taking them to their rooms. On 102 floor, there is public viewpoint. From ground floor to viewpoint you can come with elevators with speed around 30 km/h.
Interior
The Property’s amazing three-story lobby embraces visitors with sculptor Alexander Calder’s Universe, that is a mobile of various shapes, colors and movements. It is demonstrating the limitless potential of human imagination. Sears Tower lobbies are modernistic, with transparent walls and escalators piercing the vertical space. The lobby is characterized by polished granite flooring and travertine walls with stainless steel column covers. The main lobby of Sears Tower Chicago consists of one entry on the east side of the building and one entry on the west side of the building. The Wacker Drive lobby acts as the main entrance to the Property offering access from the street. The east entrance is accessed directly from Frankin Street.
Exterior
The architect and structural engineer created the Tower’s curtain wall of glass and aluminum. The curtain wall system is made of bronze-tinted vision glass and black anodized aluminum spandrels panels. Granite panels, with aluminum-framed glass hold front windows, highlight the ground level façade on the east, north and south building elevations. Building setbacks are presented on the building’s northwest and southeast corners at the 50th floor, the northeast and southwest corners at the 66th floor, and the north, south and east elevations on the 90th floor. The structural framing is composed of steel columns and beams containing nine modules. The foundation system consists of belled, reinforced concrete caissons with reinforced caisson caps. The Franklin Street entrance has a stunning large glass, aluminum and steel cover which was additional to the Property in the middle of the 1990’s.
Fire safety
Sears Tower Chicago has one of the best life protection systems for building in the world. All steel is fireproofed, programmed sprinklers cover each of the 4.5 million square feet of space. Smoke detectors are developed to discover the source of the smoke and at some point will exhaust the smoke from impacted areas. The self-contained support emergency power supply supports the alarm system, fire pumps, communication system, emergency lighting and select elevators in the occasion of an electrical malfunction. There are four two-hour, fire-rated stairwells, one of which is specifically aired for smoke-free evacuation.
Fire Sprinklers
The building is protected all through by automatic sprinklers. The Lower Level South and North Loading Docks, Level 1A parking garage and Sky Deck entry are protected by sprinkler devices. There are a total of three water tanks in the building. The water tanks can be supplied with water from the fire pumps in the areas beneath the tanks. One water tank has a 10,000-gallon capacity and two are 5,000-gallon capacity. These tanks function as a main water supply to the building fire pumps.
Sears Tower Chicago becomes Willis Tower Chicago
Changing the name of the tower which is already worldwide know by Sears Tower Chicago? It’s all a part of a bargain with the London-based Willis Group Holdings. They relocated 500 employees into 140,000 square feet on multiple floors of the 110-story building, so the Willis Group gets the naming privileges as part of it’s lease agreement with the real estate investment group that is the owner of Sears Tower Chicago. It all took place in 2011.
Willis Tower Chicago in numbers
• Height: 443 metres, with antenna 520 metres
• Ground floor: 409 000 m2
• Weight: 222 500 tonnes
• Hired workers: 16 500
• Price: 150 million US dollars