CN Tower

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Information
CN Tower
Toronto's CN Tower. The CN Tower has been the world's tallest freestanding structure on land since its opening in 1976.
Location	Toronto, Canada
Status	Complete
Constructed	1973–1976
Use	mixed use
Height
Antenna/Spire	553.3 m (1,815 ft)
Roof	457.2 m (1,500 ft)
Top floor	446.5 m (1,465 ft)
Technical Details
Floor count	181 (equivalent)
Elevator count	6
Companies
Architect	WZMH Architects

The CN Tower, at 553.33 metres (1,815 feet, 5 inches) tall, is the world's tallest freestanding structure on land. It is located in the city of Toronto, Ontario, Canada, and is considered the signature icon of the city; more than two million international visitors are attracted annually to the tower^[1]. Guinness World Records has listed the CN Tower as the world's tallest "building" for 31 years^[2].

CN originally referred to the Canadian National Railway, but following the railway's decision to divest non-core freight railway assets, prior to the company's privatization in 1995, the CN Tower was transferred to the Canada Lands Company (CLC), a federal Crown corporation responsible for real estate development. Since the citizens of Toronto wished to retain the name CN Tower, the abbreviation CN now officially stands for Canada's National rather than the original Canadian National.

1 Structure
2 History
3 Size comparisons
4 Use
5 Facts and figures
6 See also
7 References
8 External links

[edit] Structure

The CN Tower seen when looking directly up from the ground level.

The CN Tower consists of several substructures. The main portion of the Tower consists of a hollow concrete pillar containing the elevators, stairwells and power and plumbing connections. On top is the 102 m (335 ft) metal broadcast antenna, carrying TV and radio signals. There are two main visitor areas, the main seven-story pod located at the 330 m (1,100 ft) level, and the SkyPod at 447 m (1,465 ft), just below the antenna. Microwave antennas ring the lower portion of the main pod, protected in a large white donut-shaped radome.

The Sky Pod, situated high above the main observation floor, is the highest public observation deck in the world. From its top, it is possible on a clear day to see approximately 100-120 km (62-74 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.

At 342 m (1,122 ft) is the Glass Floor and Outdoor Observation Deck. The Glass Floor is 23.8 m² (256 sq ft) and can withstand a pressure of 4,100 kPa (600 lbs/sq in) or 14 large hippopotami. The glass floor consists of thermal glass units that are 64 mm (2½ in) thick, consisting of a pane of 25 mm (1 in) laminated glass, a 25 mm (1 in) airspace and a pane of 13 mm (½ in) laminated glass. Some people experience vertigo by walking out on the glass floor and looking down at the ground below.

At 346 m (1,136 ft) is the Horizons Cafe and the Lookout Level, and at 351 m (1,150 ft) is the 360 Restaurant, which completes a full revolution once every 72 minutes.

The structure's microwave receivers for distant signals are housed at 338 m (1,109 ft), and the top of the transmission antenna is at the apex of the tower.

A metal staircase with 1,776 steps reaches the Lookout level, reaching 2,579 steps by the SkyPod, and is the tallest metal staircase on earth. These stairs are intended for emergency use and are not open to the public, except for thrice 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 (the white ring around the bottom of the main pod), 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

The CN Tower under construction in 1974. The slipform is at its ultimate height. The CN roundhouse can be seen in the lower right, the Toronto Dominion Centre in the upper left.

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 Greater 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 Center (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).

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 1,000 ft (305 m) tall. Additionally, at that time most data communications took place over point-to-point microwave links, whose dish antennas 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 consisted of three independent "pillars" linked at various heights by structural bridges. This design would be considerably shorter than the Tower as it is today, the TV antenna located roughly where the concrete section between the SkyPod and Space Deck lies today. As the design effort continued, it evolved into the current design with a single continuous hexagonal core to the 447 m (1,465 ft) Space Deck level, with three support legs blended into the hexagon below the SkyPod level at 335 m (1,100 ft), forming a large Y-shape structure at the ground level.

The idea for the SkyPod in its current form evolved around this time, but the Space Deck 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.

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, 56,234 metric tonnes (62,000 tons) of dirt and shale were removed to a depth of 15 m (50 ft) in the center, and a base incorporating 7,034 m³ (9,200 cu yd) of concrete with 454 metric tonnes (500 tons) of steel re-bar and 36 metric tonnes (40 tons) of steel cable had been built to a thickness of 6.7 m (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 m (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 40 524 m³ (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 plumbobs hanging from it, observed by small telescopes from the ground. Over the height of the tower, it varies from true by only 2.9 cm (1.1 in).

In August of the same year, construction of the SkyPod 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 SkyPod, but also as a base for the construction of the SkyPod itself.

The Space Deck was built of concrete poured into a wooden frame attached to rebars at the lower level Deck, and then re-enforced 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 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 weight to 117,910 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 opened to the public on June 26, 1976, although the official opening date was October 1st. The construction costs of approximately $330 million 2005 Canadian Dollars (approximately $260 million 2005 US 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 center 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] Size comparisons

For more details on analysis of the tallest man-made structures, see World's tallest structures.

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 Free-Standing 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 m (2,063 ft) tall (see List of masts), but these are guy-wire supported structures and not classified as free-standing.

There are currently five proposals for towers whose final heights are to exceed the CN tower's^[3], three of which are currently under construction. At the forefront, the Burj Dubai would, according to present claims by its developers, become a taller free-standing land structure than CN Tower sometime in 2008; work on that tower has, as of October 31, 2006, reached the 80th floor and 277 metres (~908 ft).

View from the tower's Glass Floor.

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 of cable television soon after the tower was built which greatly reduced the need for such broadcasting centres, especially in urban areas. Only in 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

[edit] AM/FM radio

Callsign	Frequency	Band	Branding	Notes
Master FM				Consortium of Toronto broadcasters for Digital audio broadcasting
CFMJ	640 kHz	AM	AM640 Toronto Radio
CFMX	96.3 MHz	FM	Classical 96
CFNY	102.1 MHz	FM	102.1 The Edge
CFRB	1010 kHz	AM	Newstalk 1010
CFTR	680 kHz	AM	680 News
CHFI	98.1 MHz	FM	98.1 CHFI
CHIN	100.7 MHz	FM	CHIN Radio	Primarily in Italian and Portuguese
CHIN	1540 kHz	AM	CHIN Radio	Primarily in Italian and Cantonese
CHUM	104.5 MHz	FM	104.5 CHUM FM
CHUM	1050 kHz	AM	1050 CHUM
CHWO	740 kHz	AM	Prime Time Radio
CIAO	530 kHz	AM	AM 530 Multicultural Radio	Broadcasts from Brampton, Ontario
CIRC	1610 kHz	AM	--	Proposed sister station of CIRV-FM
CILQ	107.1 MHz	FM	Q107
CKFM	99.9 MHz	FM	Mix FM
CJAQ	92.5 MHz	FM	92.5 JACK FM
CJCL	590 kHz	AM	The Fan 590
CJEZ	97.3 MHz	FM	EZ Rock 97.3
CJMR	1320 kHz	AM	--	Ethnic Chinese Christian radio in Mississauga, Ontario
CJRT	91.1 MHz	FM	JAZZ.FM91

[edit] Cellular and paging providers

[edit] Communications

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

[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 over 78 times a year.
One person died during the building of the CN Tower.
The CN Tower has a wind tolerance level of 420 km/h (260 mph).
The elevators ascend and descend at over 22 km/h (15 mph), taking 58 seconds to reach the Lookout (indoor observation deck) and 61 seconds to reach the 360 restaurant levels respectively.
The Glass Floor can withstand 4,100 kPa (600 lbs/sq in) or the equivalent to 14 adult hippopotami.
In winds of 120 mph the tower sways 1.07 m (3½ ft) from centre at the Antenna, 0.46 m (1½ ft) from centre at the Space Deck, and 22.9 cm (9 inches) from centre at the Sky Pod.
The CN Tower weighs 117,910 metric tonnes (130,000 tons) as much as 20,000 elephants, and was built using 40,524 m³ (53,000 cu. yd.) of concrete, enough to build a sidewalk from Toronto to Kingston, Ontario, about 250 km (155.3 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 440 lb. piano up the stairs in 7½ 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. 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 CN Tower celebrated 30 years as the world's tallest freestanding tower on June 26, 2006.
The tower was featured in the 1995 film Canadian Bacon.
A segment of "Weird Al" Yankovic's live concerts contained a short video mockmentary 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 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.