Editing CN Tower (section)

== History ==
[[File:Toronto - ON - CN Tower bei Nacht2.jpg|thumb|left|upright|CN Tower from the [[Toronto Islands]]]]

The original concept of the CN Tower was first conceived in 1968 when the [[Canadian National Railway]] wanted to build a large television and radio communication platform to serve the Toronto area, and to demonstrate the strength of Canadian industry and CN in particular. These plans evolved over the next few years, and the project became official in 1972.

The tower would have been part of Metro Centre (see [[CityPlace, Toronto|CityPlace]]), a large development south of [[Front Street (Toronto)|Front Street]] on the [[Railway Lands]], a large railway switching yard that was being made redundant after the opening of the [[MacMillan Yard]] north of the city in 1965 (then known as Toronto Yard). Key project team members were NCK Engineering as structural engineer; [[John Andrews (architect)|John Andrews Architects]]; Webb, Zerafa, Menkes, Housden Architects; Foundation Building Construction; and Canron (Eastern Structural Division).<ref name="skyscraper" /><ref name="emporis" /><ref name="CNTower" />

As Toronto grew rapidly during the late 1960s and early 1970s, multiple skyscrapers were constructed in the downtown core, most notably [[First Canadian Place]], which has [[Bank of Montreal]]'s head offices. The reflective nature of the new buildings reduced the quality of broadcast signals, requiring new, higher antennas that were at least {{convert|300|m|ft|abbr=on}} tall. The radio wire is estimated to be {{convert|102|m|ft}} long in 44 pieces, the heaviest of which weighs around {{convert|8|t|ST LT}}.<ref>{{Cite news |last=Sienkiewicz |first=Alexandra |date=Aug 16, 2017 |title=Here's what the CN Tower was intended for, before the glass floor and EdgeWalk |publisher=CBC |url=https://www.cbc.ca/news/canada/toronto/cn-tower-beginnings-1.4249393}}</ref>

At the time, most data communications took place over [[Microwave#Communication|point-to-point microwave]] links, whose dish antennas covered 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. Had it been built, this design would have been considerably shorter, with the metal antenna located roughly where the concrete section between the main level and The Top lies today. As the design effort continued, it evolved into the current design with a single continuous hexagonal core to The Top, with three support legs blended into the hexagon below the main level, forming a large Y-shape structure at the ground level.<ref name="CNTower"/><ref name="ieee">{{cite web| author=[[The Hahn Company|TrizecHahn]]| title=A Brief Overview of the CN Tower| url=http://www.ieee.ca/millennium/cntower/cntower_overview.html| publisher=[[Institute of Electrical and Electronics Engineers]]| access-date=January 2, 2013| archive-date=March 3, 2016| archive-url=https://web.archive.org/web/20160303220107/http://www.ieee.ca/millennium/cntower/cntower_overview.html| url-status=dead}}</ref>

The idea for the main level in its current form evolved around this time, but the Space Deck (currently named The Top) was not part of the plans until 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. Also around this time, it was realized that the tower could become the world's tallest free-standing structure to improve signal quality and attract tourists, and plans were changed to incorporate subtle modifications throughout the structure to this end.<ref name="CNTower"/><ref name="ieee"/>

=== Construction ===
[[File:Ripleys Aquarium Toronto map.png|thumb|Map of the area immediately surrounding CN Tower shortly before the opening of [[Ripley's Aquarium of Canada]] in 2013]]

The CN Tower was built by Canada Cement Company (also known as the Cement Foundation Company of Canada at the time),<ref>{{cite book|last=Barr|first=Elinor|date=2015|page=173|title=Swedes in Canada: Invisible Immigrants|publisher=[[University of Toronto Press]]|isbn=978-1442613744}}</ref> a subsidiary of Sweden's [[Skanska]], a global project-development and construction group.

Construction began on February 6, 1973, with massive excavations at the tower base for the foundation. By the time the foundation was complete, {{convert|56000|t|ST LT|abbr=on|lk=on}} of [[soil|earth]] and [[shale]] were removed to a depth of {{convert|15|m|ft|1|abbr=on}} in the centre, and a base incorporating {{convert|7000|m3|cuyd|abbr=on}} of concrete with {{convert|450|t|ST LT|0|abbr=on}} of [[rebar]] and {{convert|36|t|ST LT|abbr=on}} of [[wire rope|steel cable]] had been built to a thickness of {{convert|6.7|m|ft|abbr=on}}. 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.<ref name="ieee"/>

To create the main support pillar, workers constructed a hydraulically raised [[Slip forming|slipform]] at the base. This was a fairly unprecedented engineering feat on its own, consisting of a large metal platform that raised itself on jacks at about {{convert|6|m|ft|abbr=on}} per day as the concrete below set. Concrete was poured Monday to Friday (not continuously) by a small team of people until February 22, 1974, at which time it had already become the tallest structure in Canada, surpassing the recently built {{convert|381|m|ft|adj=on}} tall [[Inco Superstack]] in [[Greater Sudbury|Sudbury]], built using similar methods.

The tower contains {{convert|40500|m3|cuyd|abbr=on}} 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 bob]]s hanging from it, observed by small telescopes from the ground. Over the height of the tower, it varies from true vertical accuracy by only {{convert|29|mm|in|1|abbr=on}}.<ref name="CNTower" /><ref name="ieee" />

[[File:CN Tower40 construction skycrane March 1975 01c.jpg|thumb|right|upright|Skycrane "Olga" lifting antenna segment]]

In August 1974, 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 used to create the brackets that support the main level, as well as a base for the construction of the main level itself. The Top was built of concrete poured into a wooden frame attached to rebar at the lower level deck, and then reinforced with a large steel compression band around the outside.<ref name="ieee"/>

While still under construction, the CN Tower officially became the world's tallest free-standing structure on March 31, 1975.<ref name=records/>

The antenna was originally to be raised by crane as well, but, during construction, the [[Sikorsky S-64 Skycrane]] helicopter became available when the [[United States Army]] sold one to civilian operators. The helicopter, named "Olga", was first used to remove the crane, and then flew the antenna up in 36 sections.

The flights of the antenna pieces were a minor tourist attraction of their own, and the schedule was printed in local newspapers. Use of the helicopter saved months of construction time, with this phase taking only three and a half weeks instead of the planned six months. The tower was topped-off on April 2, 1975, after 26 months of construction, officially capturing the height record from [[Moscow]]'s [[Ostankino Tower]], and bringing the total mass to {{convert|118000|t|ST LT|abbr=on}}.

Two years into the construction, plans for Metro Centre were scrapped, leaving the tower isolated on the Railway Lands in what was then a largely abandoned light-industrial space. This caused serious problems for tourists to access 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."<ref>{{cite book| last=Fulford| first=Robert| date=March 13, 1996| title=Accidental city: the transformation of Toronto| publisher=MacFarlane, Walter & Ross| page=32| isbn=978-0395773079}}</ref>

==== Phases of construction ====
<gallery mode="packed" heights="135px" style="text-align:left">
File:CN Tower footings 1973.jpg|Constructing the base, July 1973
File:Cntower1974.jpg|Brackets being raised, August 1974
File:CN Tower50 construction skycrane March 1975 01d.jpg|Helicopter lifting part of antenna, March 1975
File:CN Tower under construction (April 1975).jpg|Main pod construction, April 1975
File:CN Tower under construction.jpg|Nearing completion, December 1975
File:CN Tower 1976.jpg|Two months after opening, August 1976
</gallery>

=== Opening ===
The CN Tower opened on June 26, 1976.<ref>{{cite news| title=CN Tower celebrates 40 years as a tourist magnet and lightning rod| date=June 25, 2016| access-date=June 27, 2016| url=https://www.thestar.com/news/gta/2016/06/25/cn-tower-celebrates-40-years-as-a-tourist-magnet-and-lightning-rod.html| last=Botelho-Urbanski| first=Jessica| work=Toronto Star}}</ref> The construction costs of approximately {{CAD|63 million|link=yes}} (${{formatprice|{{Inflation|CA|63000000|1976}}}} in {{Inflation-year|CA}} dollars){{inflation-fn|CA}} were repaid in fifteen years.<ref>{{Cite web|title=Building the CN Tower|url=https://dozr.com/blog/building-the-cn-tower|access-date=2021-09-08|website=DOZR|language=en}}</ref>

From the mid-1970s to the mid-1980s, the CN Tower was practically the only development along Front Street West; it was still possible to see Lake Ontario from the foot of the CN Tower due to the expansive parking lots and lack of development in the area at the time. As the area around the tower was developed, particularly with the completion of the [[Metro Toronto Convention Centre]] (north building) in 1984 and SkyDome in 1989 (renamed [[Rogers Centre]] in 2005), the former Railway Lands were redeveloped 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 (Toronto)|Union Station]] railway and [[Union station (TTC)|subway station]], and, in turn, to the city's [[Path (Toronto)|Path]] underground pedestrian system. 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 [[Manhattanization|boom]] in [[condominium]] construction in [[Canadian property bubble|the first quarter of the 21st century]], as well as the 2013 opening of the [[Ripley's Aquarium of Canada|Ripley's Aquarium]] by the base of the tower.<ref name="great"/><ref name="CNTower"/><ref name="ieee"/>

===Early years ===
When the CN Tower opened in 1976, there were three public observation points: The Top (then known as the Space Deck) that stands at {{convert|447|m|ft|abbr=on}}, the Indoor Observation Level (later named Main Observation Level) at {{convert|346|m|ft|abbr=on}}, and the Outdoor Observation Terrace (at the same level as the Glass Floor) at {{convert|342|m|ft|abbr=on}}.<ref name="great"/><ref name="ieee"/> One floor above the Indoor Observation Level was the Top of Toronto Restaurant (now named "360 The Restaurant at the CN Tower"), which completed a revolution once every 72 minutes.<ref>{{cite web |title=General Information |url=https://www.cntower.ca/site_Files/Content/PDF/Press_Kit/CN_Tower_General_Information_2013_Revised.pdf |publisher=CN Tower |date=2013 |access-date=August 4, 2018 |archive-date=December 1, 2020 |archive-url=https://web.archive.org/web/20201201061602/https://www.cntower.ca/site_Files/Content/PDF/Press_Kit/CN_Tower_General_Information_2013_Revised.pdf |url-status=dead }}</ref>

The tower would garner worldwide media attention when stuntman [[Dar Robinson]] jumped off the CN Tower on two occasions in 1979 and 1980. The first was for a scene from the movie ''[[Highpoint (film)|Highpoint]]'', in which Robinson received {{CAD|250,000}} (${{Inflation|CA|250000|1979|fmt=c}} in {{Inflation-year|CA}} dollars){{inflation-fn|CA}} for the stunt. The second was for a personal [[Documentary film|documentary]]. The first stunt had him use a parachute which he deployed three seconds before impact with the ground, while the second one used a wire decelerator attached to his back.<ref name="robinson">{{cite news| title=Man Jumps From CN Tower With No Parachute (Thirty Years Ago)| url=http://torontoist.com/2010/02/man_jumps_from_cn_tower_with_no_parachute_thirty_years_ago/| first=Steve| last=Kupferman| date=February 26, 2010| work=Torontoist| access-date=November 10, 2013| archive-date=November 10, 2013| archive-url=https://web.archive.org/web/20131110154900/http://torontoist.com/2010/02/man_jumps_from_cn_tower_with_no_parachute_thirty_years_ago/| url-status=dead}}</ref>

On June 26, 1986, the tenth anniversary of the tower's opening, [[High-rise building|high-rise]] firefighting and rescue advocate [[Dan Goodwin]], in a sponsored publicity event, used his hands and feet to climb the outside of the tower, a feat he performed twice on the same day. Following both ascents, he used multiple rappels to descend to the ground.<ref>{{cite web| last=Goodwin| first=Dan| title=Dan Goodwin's Building Climbs| url=http://www.skyscraperdefense.com/building_climbs.html| publisher=Skyscraperdefense.com| access-date=January 2, 2013}}</ref>

From 1985 to 1992, the CN Tower basement level hosted the world's first flight [[simulator ride]], [[Tour of the Universe]], based on the flight of a [[Space Shuttle]]. The ride was replaced in 1992 with a similar attraction entitled "Space Race." It was later dismantled and replaced by two other rides in 1998 and 1999.

=== The 1990s and 2000s ===
A glass floor at an elevation of {{convert|342|m|ft|abbr=on}} was installed in 1994.<ref name="ieee"/> Canadian National Railway sold the tower to Canada Lands Company prior to privatizing the company in 1995, when it divested all operations not directly related to its core freight shipping businesses. The tower's name and wordmark were adjusted to remove the CN railways logo, and the tower's official name was renamed Canada's National Tower (from Canadian National Tower),<ref name="CN Tower Name">{{cite web|url=http://www.cntower.ca/portal/GetPage.aspx?at=848#The%20Tower|title="Canada's Wonder of the World"|work=CN Tower: Plan Your Visit > Who We Are|publisher=CN Tower - Canada Lands Company|access-date=February 8, 2007|archive-date=July 23, 2007|archive-url=https://web.archive.org/web/20070723015815/http://www.cntower.ca/portal/GetPage.aspx?at=848#The%20Tower|url-status=dead}}</ref> though the tower is commonly called the CN Tower.

Further changes were made from 1997 to January 2004: [[The Hahn Company|TrizecHahn Corporation]] managed the tower and instituted several expansion projects including a {{CAD|26 million}} entertainment expansion, the 1997 addition of two new elevators (to a total of six) and the consequential 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. TrizecHahn also owned the [[Willis Tower]] (Sears Tower at the time) in Chicago approximately at the same time.

In 2007, [[light-emitting diode]] (LED) lights replaced the incandescent lights that lit the CN Tower at night. This was done to take advantage of the cost savings of LED lights over incandescent lights. The colour of the LED lights can change, compared to the constant white colour of the incandescent lights. On September 12, 2007, [[Burj Khalifa]] in Dubai, then under construction and known as Burj Dubai, surpassed the CN Tower as the world's tallest free-standing structure on land.<ref name="CBCSurpassed">{{cite news| title=CN Tower dethroned by Dubai building |url= https://www.cbc.ca/news/canada/cn-tower-dethroned-by-dubai-building-1.639333 |work=[[CBC News]] |date=September 12, 2007 |access-date=April 9, 2008 |archive-url= https://web.archive.org/web/20100619095709/http://www.cbc.ca/canada/story/2007/09/12/cntower-surpassed.html |archive-date=June 19, 2010 |url-status=live |df=mdy }}</ref> In 2008, glass panels were installed in one of the CN Tower elevators, which established a world record ({{convert|346|m|ft|abbr=on}}) for highest glass floor panelled elevator in the world.

=== 2010s: EdgeWalk ===
[[File:EdgeWalk on the CN Tower.jpg|thumb|right|EdgeWalk atop the main pod]]

On August 1, 2011, the CN Tower opened the EdgeWalk, an amusement in which thrill-seekers can walk on and around the roof of the main pod of the tower at {{convert|356|m|ft|1|abbr=on}}, which is directly above the 360 Restaurant.<ref>{{cite news| title=New CN Tower attraction offers a walk on the outside| url=https://www.thestar.com/news/article/988150--new-cn-tower-attraction-offers-a-walk-on-the-outside| work=Toronto Star| access-date=January 3, 2013| date=May 9, 2011}}</ref> It is the world's highest full-circle, hands-free walk. Visitors are tethered to an overhead rail system and walk around the edge of the CN Tower's main pod above the 360 Restaurant on a {{convert|1.5|m|ft|adj=on}} metal floor.<ref>{{cite web| url=http://www.cntower.ca/en-CA/Plan-Your-Visit/Attractions/EdgeWalk/EdgeWalk-Overview.html| title=Toronto's Most Extreme Attraction| access-date=February 25, 2012| quote=It is the world's highest full circle hands-free walk on a 5 ft (1.5 metres) wide ledge encircling the top of the tower's main pod, 356m/1168ft (116 storeys) above the ground.| publisher=CN Tower| archive-date=March 9, 2012| archive-url=https://web.archive.org/web/20120309075800/http://www.cntower.ca/en-CA/Plan-Your-Visit/Attractions/EdgeWalk/EdgeWalk-Overview.html| url-status=dead}}</ref> The attraction is closed throughout the winter and during periods of electrical storms and high winds.

One of the notable guests who visited EdgeWalk was Canadian comedian [[Rick Mercer]], featured as the first episode of the ninth season of his [[CBC Television]] [[news satire]] show, ''[[Rick Mercer Report]]''. There, he was accompanied by Canadian pop singer [[Jann Arden]]. The episode first aired on April 10, 2013.<ref>{{cite web|url=http://www.cbc.ca/mercerreport/episodes/season-9/season-9-episode-1|title=Season 9 - Episode 1|series=Rick Mercer Report|date=April 10, 2013|work=CBC Television}}</ref>

==== 2015 Pan Am Games ====
The tower and surrounding areas were prominent in the [[2015 Pan American Games]] production. In [[2015 Pan American Games opening ceremony|the opening ceremony]], a pre-recorded segment featured track-and-field athlete [[Bruny Surin]] passing the flame to sprinter [[Donovan Bailey]] on the EdgeWalk and parachuting into Rogers Centre. A fireworks display off the tower concluded both the opening and closing ceremonies.

==== Canada 150 ====
On July 1, 2017, as part of the nationwide celebrations for [[150th anniversary of Canada|Canada 150]], which celebrated the 150th anniversary of [[Canadian Confederation]], fireworks were once again shot from the tower in a five-minute display coordinated with the tower lights and music broadcast on a local radio station.

=== 2020s ===
The CN Tower closed during much of the [[COVID-19 pandemic]]. During much of the pandemic, the gift shop was renovated to take advantage of the lack visitors from the tower's closure.