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Monday, March 29, 2010

CN Tower

The CN Tower, located in downtown Toronto, Ontario, Canada, is a communications and observation tower standing 553.3 metres or 1,815 ft tall. It surpassed the height of the Ostankino Tower while still under construction in 1975, becoming the tallest free-standing structure on land in the world for the next 31 years. On September 12, 2007 the CN Tower was surpassed in height by Burj Khalifa. It remains the tallest free-standing structure in the Western Hemisphere, the signature icon of Toronto's skyline, and a symbol of Canada, attracting more than two million international visitors annually.

CN TowerCN originally referred to Canadian National, the railway company that built the tower. Following the railway's decision to divest non-core freight railway assets, prior to the company's privatization in 1995 it transferred the tower to the Canada Lands Company, a federal Crown corporation responsible for real estate development. Since local residents wished to retain the name CN Tower, the abbreviation is now said to expand to Canada's National Tower rather than the original Canadian National Tower; however, neither of these names are commonly used.

In 1995, the CN Tower was declared one of the modern Seven Wonders of the World by the American Society of Civil Engineers. It also belongs to the World Federation of Great Towers, where it holds the 1st place ranking. Construction on the CN Tower began on February 6, 1973 with massive excavations at the tower base for the foundation. By the time the foundation was complete, 56,000 t of dirt and shale were removed to a depth of 15 metres or 49.2 ft in the centre, and a base incorporating 7,000 cubic metres or 9,156 cu yd of concrete with 450 tonnes of rebar and 36 tonnes of steel cable had been built to a thickness of 6.7 metres or 22.0 ft. This portion of the construction was fairly rapid, with only four months needed between the start and the foundation being ready for construction on top.

The CN Tower consists of several substructures. The main portion of the tower is a hollow concrete hexagonal pillar containing the six elevators, stairwells, and power and plumbing connections. On top of this is a 102-metre or 334.6 ft tall metal broadcast antenna, carrying TV and radio signals. There are two visitor areas: the main deck level located at 346 metres or 1,135 ft, and the higher Sky Pod at 446.5 metres or 1,465 ft, just below the metal antenna. The hexagonal shape can be seen between the two areas; however, below the main deck, three large supporting legs give the tower the appearance of a large tripod.

The main level is seven storeys, some of which are open to the public. Below the public areas at 338 metres or 1,108.9 ft is a large white donut-shaped radome containing the structure's microwave receivers. The glass floor and outdoor observation deck are at 342 metres or 1,122.0 ft. The glass floor has an area of 24 square metres or 258 sq ft and can withstand a pressure of 4,100 kilopascals or 595 psi. The floor's thermal glass units are 64 millimetres or 2.5 in thick, consisting of a pane of 25-millimetre or 1.0 in laminated glass, 25 millimetres or 1.0 in airspace and a pane of 13-millimetre or 0.5 in laminated glass. Some people experience acrophobia when standing on the glass floor and looking down at the ground 342 metres or 1,122.0 ft below.

CN TowerCN Tower

In 2008, one elevator was upgraded to add a glass floor panel, believed to have the highest vertical rise of any elevator equipped with this feature. The Horizons Cafe and the lookout level are at 346 metres or 1,135.2 ft. The 360 Restaurant, a revolving restaurant that completes a full rotation once every 72 minutes, is at 351 metres or1,151.6 ft. When the tower first opened, it also featured a disco named Sparkles, billed as the highest disco and dance floor in the world. The Sky Pod is the second-highest public observation deck in the world, surpassed only by the Shanghai World Financial Center. On a clear day, it is possible to see 100 to 120 kilometres or 62–75 miles away, to the city of Rochester across Lake Ontario in the United States, the mist rising from Niagara Falls, or the shores of Lake Simcoe.

A metal staircase reaches the main deck level after 1,776 steps, and the Sky Pod 100 metres above after 2,579 steps. It is the tallest metal staircase on Earth. These stairs are intended for emergency use only and are not open to the public, except for two times per year for charity stair-climb events. In June 2007, the tower was outfitted with 1,330 super-bright LED lights inside the elevator shafts, shooting up over the bubbleand upward to the top of the tower's mast to light the tower from dusk until 2 a.m.

The official opening ceremony took place on June 28 before the Canada Day holiday weekend. The tower changes its lighting scheme on holidays and to commemorate major events. After the 95th Grey Cup in Toronto, the tower was lit up in green and white to represent the colours of the Grey Cup champion Saskatchewan Roughriders. Guinness World Records has called the CN Tower the world's tallest self-supporting tower and "the world's tallest free-standing tower Although Guinness did list this description of the CN Tower under the heading "tallest building at least once, it has also listed it under tallest tower, omitting it from its list of "tallest buildings.

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