History

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 mass to 117,910 metric tonnes (a weight of 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.

ANNOTATIONS

deck – платформа, apex – вершина, evolve – развиваться, downtown core - деловой центр города, broadcasting – трансляция, dish antenna – зеркальная антенна, concrete – бетон, ludicrous – смешной

Comprehension Check Exercises

I. Fill in the blank with the correct word:

1. The CN Tower has been the world's tallest freestanding structure on land since its opening in ….

2. Its location is ….

3. The abbreviation CN now officially stands for ….

4. The Sky Pod, situated high above the main observation floor, is the highest … in the world.

5. The original plan for the tower consisted of three independent "pillars" linked at various heights by ….

6. As the area around the Tower was developed, the former railway "wasteland" disappeared and the Tower became the centre of ….

II. Find out whether the statement is true or false according to the information in the text:

1. Guinness World Records has listed the CN Tower as the world's tallest "building" for 100 years.

2. A metal staircase with 1,776 steps reaches the Lookout level, reaching 2,579 steps by the SkyPod is open to the public.

3. 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).

4. 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.

5. Construction on the CN Tower started on February 6, 1937.

III. Questions:

1. What does the CN Tower consist of?

2. What did the concept of the CN Tower originate from?

3. When did the CN Tower open to the public?

IV. Do you remember?

1. What did originally CN refer to?

2. Who was the project architect?

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