CN Tower

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CN Tower
Toronto's CN Tower. The CN Tower has been the world's tallest building and freestanding structure on land since its opening in 1976.
Information
Location	Toronto, Ontario, Canada
Status	Complete
Constructed	1973 – 1976
Use	mixed use
Height
Antenna/Spire	553 m (1,815 ft)
Roof	554 m (1,500 ft)
Top floor	446 m (1,465 ft)
Technical Details
Floor count	181 (equivalent)
Elevator count	6
Companies
Architect	WZMH Architects

The CN Tower, located in Toronto, Ontario, Canada, is the world's tallest freestanding structure on land, standing 553.33 meters (1,815 ft 5 in) tall. It is considered the signature icon of the city, attracting more than two million international visitors annually.^[1] Guinness World Records has listed the CN Tower as the world's tallest building since its completion in 1976. From a technical perspective, however, it is not considered a building by the Council on Tall Buildings and Urban Habitat, which ranks tall buildings.

[edit] Structure

The CN Tower consists of several substructures. The main portion of the Tower consists of a hollow concrete hexagonal pillar containing the elevators, stairwells and power and plumbing connections. On top of this is the 102 metre (335 ft) metal broadcast antenna, carrying TV and radio signals. There are two main visitor areas: the main seven-story deck level located at 330 metre (1,100 ft), and the higher Sky Pod (formerly known as Space Deck) at 447 metres (1,465 ft), just below the metal antenna. Between the two areas the structure is "bare" and the hexagonal shape can be seen, but below the main deck three large supporting legs give the tower the appearance of a large tripod. Confusingly, the main level used to be known as “SkyPod”, a name which now refers to the higher level.

The main level consists of several floors, some open to the public. At 342 metres (1,122 ft) is the Glass Floor and Outdoor Observation Deck. The glass floor has an area of 24 square metres (256 sq ft) and can withstand a pressure of 42 kg•f/cm² (600 psi). The glass floor consists of thermal glass units that are 64 millimetres (2.5 in) thick, consisting of a pane of 25 millimetres (1 in) laminated glass, a 25 millimetre (1 in) airspace and a pane of 13 millimetres (0.5 in) laminated glass. Some people experience acrophobia by walking out on the glass floor and looking down at the ground below. At 346 metres (1,136 ft) is the Horizons Cafe and the Look Out level, and at 351 metres (1,150 ft) is the 360 Restaurant, which completes a full revolution once every 72 minutes. Below these areas are the structure's microwave receivers in a large white donut-shaped radome, at 338 metres (1,109 ft).

Inside the 360 Restaurant.

The Sky Pod is the highest public observation deck in the world. From its top, it is possible on a clear day to see approximately 100 to 120 kilometres (60–75 mi) away and even see an outline of the city of Rochester across Lake Ontario in the United States, or the mist rising from Niagara Falls.

A metal staircase with 1,776 steps reaches the main deck level, reaching 2,579 steps by the Sky Pod, and is the tallest metal staircase on Earth. These stairs are intended for emergency use and are not open to the public, except for three times per year for charity stair-climb events: around Earth Day in the spring by the World Wildlife Fund and in the fall by the United Way's Toronto chapter. The average climber takes approximately 30 minutes to climb to the base of the radome, but the fastest climb on record is 7 minutes and 52 seconds in 1989 by Brendan Keenoy, an Ontario Provincial Police Officer. The fastest record for a woman belongs to Chrissy Redden, who climbed the stairs in 2000 in 11 minutes and 52 seconds. In 2002, Canadian Olympian & Paralympic Champion Jeff Adams climbed the stairs of the CN Tower in a specially designed wheelchair.

[edit] History

[edit] Conception

The concept of the CN Tower originated from a 1968 Canadian National Railway desire to build a large TV and radio communication platform to serve the Toronto area, as well as demonstrating the strength of Canadian industry, and CN in particular. These plans evolved over the next few years, until the project became "official" in 1972. The Tower would have been part of Metro Centre (see CityPlace), a large development south of Front Street on the Railway Lands, a large railway switching yard that was being made redundant by newer yards outside the city. Key project team members were NCK Engineering as structural engineer; John Andrews Architects; Webb, Zerafa, Menkes, Housden Architects; Foundation Building Construction and Canron (Eastern Structural Division).

The City of Toronto, Fall, as seen from the Outdoor Observation Deck looking northwest. Rogers Centre is off-frame to the lower left, and downtown to the right. The northern portion Trinity-Bellwoods Park is just visible in the upper-left of the image, see below for the "reverse angle" from the park. The road running diagonally from the lower left to upper right is Spadina, its separate streetcar right-of-way is visible in the middle of the road.

At the time, Toronto was a "boom town" and the late 1960s and early 1970s had seen the construction of numerous large skyscrapers in the downtown core. This made broadcasting into the downtown area very difficult due to reflections off the buildings. The only solution would be to raise the antennas above the buildings, demanding a tower over 300 metres (1,000 ft) tall. Additionally, at that time most data communications took place over point-to-point microwave links, whose dish antennae used to cover the roofs of large buildings. As each new skyscraper was added to the downtown, former line-of-sight links were no longer possible. CN intended to rent "hub" space for microwave links, visible from almost any building in the Toronto area.

The original plan for the tower envisioned a tripod consisting of three independent cylindrical "pillars" linked at various heights by structural bridges. This design would be considerably shorter than the Tower as it is today, the metal antenna located roughly where the concrete section between the main level and the Sky Pod lies today. As the design effort continued, it evolved into the current design with a single continuous hexagonal core to the 447 metre (1,465 ft) Sky Pod, with three support legs blended into the hexagon below the main level, forming a large Y-shape structure at the ground level.

The idea for the main level in its current form evolved around this time, but the Sky Pod was not part of the plans until some time later. One engineer in particular felt that visitors would feel the higher observation deck would be worth paying extra for, and the costs in terms of construction were not prohibitive. It was also some time around this point that it was realized that the Tower could become the world's tallest structure, and plans were changed to incorporate subtle changes throughout the tower to this end.

[edit] Construction

Construction on the CN Tower started on February 6, 1973 with massive excavations at the tower base for the foundation. By the time the foundation was complete, 56,000 metric tonnes (62,000 short tons) of dirt and shale were removed to a depth of 15 metres (50 ft) in the centre, and a base incorporating 7,000 cubic metres (9,200 cu yd) of concrete with 450 metric tonnes (500 tons) of steel re-bar and 36 tonnes (40 tons) of steel cable had been built to a thickness of 6.7 metres (22 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.

To build the main support pillar, a hydraulically-raised slipform was built at the base. This was a fairly impressive engineering feat on its own, consisting of a large metal platform that raised itself on jacks at about 6 metres (20 ft) per day as the concrete below set. Concrete was poured continuously by a team of 1,537 people until February 22, 1974, during which it had already become the tallest structure in Canada, surpassing the recently built Superstack which was built using similar methods. In total, the tower contains 40,500 cubic metres (53,000 cu yd) of concrete, all of which was mixed on-site in order to ensure batch consistency. Through the pour, the vertical accuracy of the tower was maintained by comparing the slip form's location to massive plumb bobs hanging from it, observed by small telescopes from the ground. Over the height of the tower, it varies from true by only 29 mm (1.1 in).

A bolt of lightning strikes the CN Tower on August 2, 2006.

In August of the same year, construction of the main level commenced. Using 45 hydraulic jacks attached to cables strung from a temporary steel crown anchored to the top of the tower, twelve giant steel and wooden bracket forms were slowly raised, ultimately taking about a week to crawl up to their final position. These forms were not only used to create the brackets which support the main level, but also as a base for the construction of the main level itself. The Sky Pod was built of concrete poured into a wooden frame attached to rebars at the lower level Deck, and then reinforced with a large steel compression band around the outside.

The antenna was originally to be raised by crane as well, but during construction the Sikorsky Skycrane helicopter became available when the US Army sold off their examples to civilian operators. The helicopter, named "Olga", was first used to remove the crane, and then flew the antenna up in 36 sections. Flights were a minor tourist attraction of their own, and the schedule was printed in the local newspapers. Use of the helicopter saved months of construction time, with this phase taking only 3 and a half weeks instead of the planned six months. The tower was topped off on April 2, 1975 after 40 months of construction, officially capturing the height record from Moscow's Ostankino Tower, and bringing the total mass to 118,000 metric tonnes (130,000 tons).

Two years into the construction, plans for Metro Centre were scrapped, leaving the Tower isolated on the Railway Lands in what was then largely abandoned light-industrial space. This caused serious problems with access to the tower. Ned Baldwin, project architect with John Andrews, wrote at the time that "All of the logic which dictated the design of the lower accommodation has been upset," and that "Under such ludicrous circumstances Canadian National would hardly have chosen this location to build."

The CN Tower as seen from its base

[edit] Opening

The CN Tower opened to the public on June 26, 1976, although the official opening date was October 1. The construction costs of approximately $75,000,000 ($330,000,000 2005) Canadian dollars were repaid in fifteen years. CN sold the Tower prior to taking the company public in 1995, when they decided to divest themselves of all operations not directly related to their core freight shipping businesses.

As the area around the Tower was developed, particularly with the introduction of the Metro Toronto Convention Centre and Skydome (known as the Rogers Centre since 2005), the former railway "wasteland" disappeared and the Tower became the centre of a newly developing entertainment area. Access was greatly improved with the construction of the SkyWalk in 1989, which connected the Tower and SkyDome to the nearby Union Station railway and subway station. By the mid-1990s it was the centre of a thriving tourist district. The entire area continues to be an area of intense building, notably a recent boom in condominium construction. Although the area did not develop as CN and CP initially planned, along an east-west axis, in the end the Tower terminated a long view south down John Street from Toronto's "entertainment district".

From 1997 to January 2004, TrizecHahn Corporation managed the building and instituted several expansion projects including a $26 million entertainment expansion and revitalization that included the addition of two new elevators (to a total of six) and the relocation of the staircase from the north side leg to inside the core of the building, a conversion that also added nine stairs to the climb.

[edit] March 2007 Falling Ice Danger

In early March 2007, local streets and a section of the Gardiner Expressway were closed due to ice falling from the CN Tower. There were fears that cars and windows of nearby buildings would be smashed by large chunks of ice. It was the first time such an event had posed a threat to public safety. A freezing rain storm on March 2 had resulted in a layer of ice several centimetres thick forming on the side of the tower. The sun thawed the ice, and winds of up to 90 kph caused some of it to dislodge and be blown away from the structure. At the height of morning rush hour on March 5, police expanded the area of closed streets to include the nearby highway, as winds caused the ice to be blown further away. Ice was blown from the Tower and other downtown buildings (e.g., BCE Place) to as far north as King Street, where a cab window was shattered. On March 6, 2007, The Gardiner Expressway was reopened after winds died down.

CityNews Video: Ice Falling from CN Tower

[edit] Size comparisons

View from the tower's Glass Floor.

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. The following year, the Guinness Book of World Records officially changed the CN Tower's classification to "World's Tallest Building and Freestanding Structure". Today, the Guinness World Records state the CN Tower as the "Tallest Freestanding Tower". This is because the Petronius Platform oil rig in the Gulf of Mexico is taller, yet most of the rig is underwater.

There are also many guyed towers taller than the CN Tower, the current tallest being the KVLY-TV tower in North Dakota at 628 metres (2,063 ft) tall (see List of masts), but these are guy-wire supported structures (which are essentially very tall frameworks that support TV lines) and hence, are not classified as freestanding.

There are currently five proposals for towers whose final heights are to exceed the CN tower's^[2], three of which are currently under construction. At the forefront, the Burj Dubai would, according to present claims by its developers, become a taller freestanding land structure than CN Tower sometime in 2008; work on that tower has, as of January 31, 2007, reached the 110th floor and 411 metres (1,348 ft).

The builders of the CN Tower did not expect that it would hold the tallest structure record for thirty years. Previous record holders had quickly been supplanted. Several rivals have been proposed and most schemes collapsed. This is partly due to the development, soon after the tower was built, of cable television, which greatly reduced the need for such broadcasting centres, especially in urban areas. Only in large cities are there enough tourists to make such a tower viable as a tourist attraction.

[edit] Use

The CN Tower has been and continues to be used as a communications tower for a number of different media, and by numerous companies:

[edit] Television broadcasters

• CBC
• CTV Toronto
• Citytv Toronto
• CablePulse 24
• Global Ontario
• LOOK TV (a digital cable provider)
• Rogers Cable
• SUN TV

[edit] AM/FM radio

[edit] Cellular and paging providers

• Bell Mobility
• Rogers Wireless
• Motorola

[edit] Communications

• Bell Canada
• Toronto Transit Commission
• Amateur radio repeaters "2-Tango" (2 m VHF) and "4-Tango" (440/70 cm UHF) – owned and operated by the Toronto FM Communications Society, under callsign VE3TWR.^[3]

[edit] Facts and figures

The CN Tower, as seen from Trinity Bellwoods Park on the west side of Toronto

• The CN Tower is 13 metres taller than Moscow's Ostankino Tower, is almost twice as tall as the Eiffel Tower, and is the tallest member of the World Federation of Great Towers.
• The CN Tower is struck by lightning at least 40 to 50 times annually compared to other places in Toronto which are struck, on average, two times per square kilometre every year.^[4]
• One person died during the building of the CN Tower.
• The CN Tower has a wind tolerance level of 420 km/h (117 m/s) (260 mph).
• The elevators ascend and descend at over 22 km/h (6 m/s) (15 mph), taking 58 seconds to reach the Look Out level (indoor observation deck) and 61 seconds to reach the 360 restaurant levels.
• The Glass Floor can withstand 4,100 kPa (600 lbf/in²).
• In winds of 200 km/h (120 mph) the tower sways 1.05 m (3½ ft) from centre at the Antenna, 0.45 m (1½ ft) from centre at the Sky Pod, and 0.25 m (9 in) from centre at the main level.
• The CN Tower has a mass of 118,000 Mg (130,000 tons), and was built using 40,500 m³ (53,000 yd³) of concrete, enough to build a sidewalk from Toronto to Kingston, Ontario, about 250 km (150 mi) away.
• A Sikorsky Skycrane helicopter nicknamed 'Olga' was used to lower the communications antenna into place on the tower. The helicopter was piloted by Larry Pravecek.
• The CN Tower is designed to withstand an earthquake of 8.5 on the Richter Scale.
• In 1979, Norman Alexander and Joe Squire hauled a 200 kg (440 lb) piano up the stairs in 7.5 hours.
• On July 23, 1999, Ashrita Furman became the fastest person to go up the CN Tower using a pogo stick.
• In 2001, a group of environmentalists illegally scaled the outside of the Tower, in order to place a banner protesting the policies of United States President George W. Bush.
• The tower is the only landmark from Canada that appears in the city-building/simulation computer games SimCity 3000 and SimCity 4.
• The CN Tower was included in the Namco pilot simulation game Ace Combat 5: The Unsung War. The tower rests in a fictional metropolitan area named November City.
• The tower is occasionally mistaken by some for the Seattle Space Needle, due to their similar appearances, however the CN Tower is exactly three times taller than the Space Needle. While filming in Toronto, American talk show host Conan O'Brien staged a mock fight on his show between two men costumed as the respective towers.
• The CN Tower can be accidentally seen numerous times during scenes in the Police Academy series.
• The vertical warning marker lights of the CN Tower can be accidentally seen in the movie Bulletproof Monk during scenes shot at night.
• The CN Tower celebrated 30 years as the world's tallest building June 26, 2006. CN Tower staff specifically ignored the Council on Tall Buildings and Urban Habitat view on their status as a building.
• The tower was featured in the 1995 film Canadian Bacon.
• A segment of "Weird Al" Yankovic's live concerts contained a short video mockumentary about why it is inadvisable to throw bananas from the top of the CN Tower.
• The song "The CN Tower Belongs to the Dead" by Owen Pallett makes obvious reference to the Tower.
• The song "I Don't Want to Go to Toronto" by Radio Free Vestibule complains that "there's a tower in Toronto that controls people's minds," an obvious reference to the CN Tower.
• The CN Tower was featured on the front cover of the 1996 Guinness Book of World Records^[5].
• The CN Tower is featured in the music video of Another Postcard, a song on the 2003 Everything to Everyone album by the Barenaked Ladies.
• In April 2006, Braden Fox, a Humber College firefighting student climbed the stairs in full turnout gear to raise money for the World Wide Fund for Nature (WWF). His time of 20 minutes 43 seconds beat the previous record for such a feat by over two full minutes.
• The CN tower (along with the rest of the Toronto skyline) can be seen easily on a clear day from the shore of Lake Ontario and the brim of the Niagara Escarpment in the Niagara Peninsula.
• Tour of the Universe was a space ride located in the base from 1986 to 1987
• The movie Highpoint (1982) includes the highest stunt fall in motion pictures. Dar Robinson falls from the tower, a height of 1,170 feet, before opening his parachute 90 meters above the ground. His pay was $150,000 for the stunt.

[edit] Media placement

• Police Academy 3: Back in Training
• Strange Brew
• The Sentinel
• Resident Evil: Apocalypse
• Exit Wounds
• Canadian Bacon
• Highpoint (1982)

[edit] See also

• Tallest free standing structure on land
• List of towers
• List of masts
• List of skyscrapers
• List of tallest structures in Canada
• World's tallest structures
• CityPlace (Toronto)

[edit] References

[edit] External links

Wikimedia Commons has media related to:

CN Tower

• Official site of the CN tower
• What is the tallest building in the world?
• Google Satellite Image
• CN Tower in 3D on Google Earth
• 25 Tallest Buildings in Toronto
• Flicker CN Tower Photos*
• Emporis CN Tower listing
• Youtube movie of CN Tower
• Google Sketchup ~ CN Tower 3D Model-Full Scale
• Location of the CN Tower along with photos, videos, and other web pages related to the area

Coordinates: 43°38′33.24″N, 79°23′13.7″W