City
The CN Tower turns 35-years-old
Happy 35th birthday, CN Tower! What would Toronto's skyline be without you? In honour of this occasion (which actually took place yesterday), I think it's fitting to look back at your birth, so to speak.
Although construction on the tower began in 1973, its conception dates back to 1968 and one of many plans to revitalize Toronto's downtown railway lands was proposed in the form of the Metro Centre. Although the larger plan — which called for the demolition of Union Station — never came to be, the idea of a major communications tower survived Metro Centre's demise. Fortunately, the original plans for the tower, which featured three cylinders of various lengths, were also abandoned in favour of the current design.
Along with its symbolic function as an illustration of CN's prosperity, the tower served a rather pragmatic purpose when it was built. On account of the rise of modern skyscrapers in Toronto (starting in 1968 with the TD Centre), the quality of television broadcasts was severely compromised by signal reflection. To solve the problem, the tower would need to be taller than the other buildings in the downtown core, which it is to this day.
After the foundation had been laid in a rather speedy four months, construction began on the tower portion, which gradually proceeded upwards via the use of a slipform, which allowed for concrete to be poured seamlessly rather than in pieces. By late summer of 1974, work had commenced on the main pod, which is itself seven-storeys high. The radome at the bottom of this section is were the communications equipment is housed.
The final stage of construction involved the antenna section, which was assembled via 36 separate pieces. The original plan was to use a crane for this part of the work, but a Skycrane helicopter was used instead, which saved considerable time. The tower was topped off on April 2, 1975 and eventually opened on June 26, 1976. Since that time, it has served as the centrepiece of our skyline and the city's most recognized icon.
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Video from the CBC Archives. Photos from the Toronto Archives (where marked), Photoscream, Time Magazine, and squirrel brand (last).
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It really was an elegant and simple solution to an engineering and social problem unique to Toronto. Since Canadians had long been addicted to American TV, people in Toronto pointed their antennae south towards Rochester and Buffalo to pick up their channels. (Remember, this is all before cable.) This made it tough for the Canadian broadcasters, who were broadcasting out of places in the suburbs to the north and east (like CFTO in Agincourt.)
So the solution was obvious -- to put a large TV mast as far south as possible, so that people could point their antennae south and get both Canadian stations from the TV mast and US stations from over the lake.
As skyscrapers had suddenly appeared in 1970s Toronto, a calculation had to be made as to a reasonable height for the microwave transmitters. It was predicted that no building in Toronto would ever exceed the 1,000 ft height of First Canadian Place, so the microwave/TV pod (and main communications area) was set at 1,100 ft to give a 100 ft clear separation. There had to be a further 700 ft separation between the microwave and radio antenna, making the top of the tower around 1,800 ft.
That's really all there was to it. Throw in some elevators, observation decks and restaurant and you have the CN Tower. It's interesting that HDTV has given Over-the-air a new lease on life -- I imagine many antennae in Toronto are now once more pointing south towards the big spire by the lake.
For example, as of 1995 the concrete in the Hoover Dam was still strengthening (it was over 60 years old at that point). Concrete is definitely one of the most amazing building materials.
Neat to see the photos from the time, especially to see how much the skyline has changed in that time.