Civil Engineering Projects Online

The Sears Tower is a skyscraper in Chicago, Illinois. It has been the tallest building in the United States since 1973, surpassing the World Trade Center, which itself had surpassed the Empire State Building only a year earlier. Commissioned by Sears, Roebuck and Company, it was designed by chief architect Bruce Graham and structural engineer Fazlur Khan of Skidmore, Owings and Merrill.

Construction commenced in August 1970 and the building reached its originally anticipated maximum height on May 3, 1973. When completed, the Sears Tower had overtaken the roof of the World Trade Center in New York City as the world’s tallest building. The tower has 108 stories as counted by standard methods, though the building owners count the main roof as 109 and the mechanical penthouse roof as 110. The distance to the roof is 1,451 feet (442 m), measured from the east entrance.

In February 1982, two television antennas were added to the structure, increasing its total height to 1,705 feet (520 m). The western antenna was later extended to 1,730 feet (527 m) on June 5, 2000 to improve reception of local NBC station WMAQ-TV.

Black bands appear on the tower around the 29th–32nd, 64th–65th, 88th–89th, and 104th–109th floors. These are louvers which allow ventilation for service equipment and obscure the structure’s belt trusses which Sears Roebuck did not want to be visible as on the John Hancock Center.

The building’s official address is 233 South Wacker Drive, Chicago, Illinois 60606.

On August 12, 2007, the Burj Dubai in Dubai, United Arab Emirates was reported by its developers to have surpassed the Sears Tower in all height categories. It overtook the Sears Tower antenna 1,730 feet (527 m) and as of February 18, 2008, the building stands at least 254 feet (77 m) taller at 1,984.6 feet (604.9 m).

History of Sears Towers

In 1969, Sears, Roebuck & Co. was the largest retailer in the world, with about 350,000 employees. Sears executives decided to consolidate the thousands of employees in offices distributed throughout the Chicago area into one building on the western edge of Chicago’s Loop. With immediate space demands of 3 million square feet (279,000 m²), and with predictions and plans for future growth necessitating even more space than that, architects for Skidmore knew that the building would be one of the largest office buildings in the world.

Sears executives decided early on that the space they would immediately occupy should be efficiently designed to house the small army that was their Merchandise Group. However, floor space for future growth would be rented out to smaller firms and businesses until Sears could retake it. Therefore, the floor sizes would need to be smaller, and to have a higher window-space to floor-space ratio, to be more attractive and marketable to these prospective lessees. Smaller floor sizes necessitated a taller structure. Skidmore architects proposed a tower which would have large 55,000-square-foot (5,000 m²) floors in the lower part of the building, and would gradually taper the area of the floors down in a series of setbacks, which would give the Sears Tower its distinctive, husky-shouldered look.

As Sears continued to offer optimistic projections for future growth, the tower’s proposed height soared into the low hundreds of floors and surpassed the height of New York’s unfinished World Trade Center to become the world’s tallest building. Restricted in height not by physical limitation or imagination but rather by a limit imposed by the Federal Aviation Administration to protect air traffic, the Sears Tower would be financed completely out of Sears’ deep pockets, and topped with two antennas to permit local television and radio broadcasts. Sears and the City of Chicago approved the design, and the first steel was put in place in April 1971. The structure was completed in May 1973. Construction costs totaled approximately $150 million USD at the time, which would be equivalent to roughly $950 million USD in 2005. For comparison, Taipei’s Taipei 101, built in 2004, cost around the equivalent of US$1.64 billion in 2005 dollars.

Sears Tower has gone through several owners in the years since but Sears has retained the naming rights for the building. It is now a multi-tenant office building with more than 100 different companies in residence, including major law firms, insurance companies and financial services firms.

The SkyDeck

The Sears Tower Skydeck observation deck opened on June 22, 1974 and is located on the 103rd floor of the tower. It is 1,353 feet (412 m) above ground and is one of the most famous tourist attractions in Chicago. Tourists can experience how the building sways on a windy day. They can see far over the plains of Illinois and across Lake Michigan to Indiana, Michigan and Wisconsin on a clear day. It takes about 45 seconds to soar to the top in either of two special elevators. The Sears Tower Skydeck competes with the John Hancock Center’s observation floor a mile and a half away, which is 323 feet (98 m) lower. 1.3 million tourists visit the Skydeck anually.

A second Skydeck on the 99th floor is used when the 103rd floor is closed. The tourist entrance can be found on the south side of the building along Jackson Boulevard.

Facts about Sears Towers

* The top of the Sears Tower is the highest point in Illinois. The tip of its highest antenna is 1,730 feet (527.3 m) or 2,325 feet (708 m) above sea level, its roof is 1,451 feet (442.3 m) above street level or 2,046 feet (623 m) above sea level, the 103rd floor observation deck (The Sky deck) is 412 m (1,353 ft) above street level or 1,948 feet (593 m) above sea level, the Wacker Drive main entrance is 595 feet (181 m) above sea level. (The highest natural point in Illinois is the Charles Mound, at 1,235 feet (376 m) above sea level.)
* The building leans about 4 inches (10 cm) from vertical due to its slightly asymmetrical design, placing unequal loads on its foundation. This can occasionally be felt.
* The antennas atop the Sears Tower are struck by lightning an average of 650-675 times per year.
* The design for the Sears Tower incorporates nine steel-unit square tubes in a 3 tube by 3 tube arrangement, with each tube having the footprint of 75 x 75 feet (22 x 22 m). The Sears Tower was the first building for which this design was used. The design allows future growth of extra height to the tower if wanted or needed.
* The restrooms on the 103rd floor sky deck 1,353 feet (412 m) above street level are the highest in the world.

Wednesday, April 9th, 2008 @ 10:03 pm Civil Engineering, Tall Buildings
RSS 2.0 Trackback