CN Tower
Location: Toronto, ON
Year Completed: 1976
Height: 1,815 feet
Claim to Fame: The tallest freestanding structure on Earth, supplanting the Ostankino Tower in Moscow.
As the TD Tower neared completion in Toronto in 1967, nay-sayers expressed doubts that the million-square-foot building could be filled with tenants given the number of new office buildings then under construction in the city, including the 600-foot Royal Trust Tower that was already slated to go up adjacent to the TD Tower as part of the same project.
And this was Toronto, a city whose population was watching Ed Sullivan and
Hee Haw on Buffalo TV stations.
If Toronto was a hard sell when it came to skyscrapers, then the reluctance of London and Frankfurt to build them makes a lot more sense.
The mid-1960s business boom, however, was more than up to the task of filling the TD Centre, and the TD Tower was 90% occupied within 18 months of its completion while the Royal Trust Tower was pre-sold before it even opened in 1969.
Toronto skyline in 1970, dominated by the TD Tower and Royal Trust Tower
The year Apollo 11 landed on the moon, the sky no longer seemed the limit. Build it, and they will come.
That year, the Toronto Stock Exchange traded 2,000,000 shares in a single day for the first time — up from 1,000,000 just five years earlier, and business had never been better in Toronto. The old colonial finance system based in London had faded away, and indeed Toronto had supplanted Montreal as Canada’s chief financial centre and was now engaged to an ever-increasing degree with New York, Chicago and Tokyo.
The air was electric.
Well, except that broadcasting in the fast-rising city was becoming a problem.
TV and radio signals in the downtown where bouncing off the buildings. The
bon mots exchanged on
Gilligan's Island could barely be heard amongst the static and ghost images.
Ironically, mitigating the dileterious effects on broadcasting caused by tall buildings would result in the construction of the tallest structure of them all.
One solution would be to raise the broadcast antennas above the buildings, demanding a tower over 1,000 feet tall. At that time most data communications took place over point-to-point microwave links using dish antennas on the roofs of large buildings. As each new skyscraper was erected downtown, former line-of-sight links were being broken. The Canadian National Railway, which owned land on Toronto's lakefront, decided to build a series of communciations masts to serve as a ‘hub’ for microwave links on a tower visible from almost any building in Toronto.
In 1968, the plan called for three pillars linked at various heights by structural bridges, with the tallest TV antenna rising roughly 1,500 feet above the ground, and the other two standing 1,200 and 1,100 feet tall.
As the design proceeded, this concept evolved into a single hexagonal concrete shaft rising 1,465 feet, with three support legs joined to the shaft at the 1,100-foot level, forming a large Y-shaped footprint at the base. It was a spartan and industrial design — a bit too spartan to be accepted adjacent to downtown by Toronto City Hall.
The central concrete core of the CN Tower
So, in 1971 an open-air observation deck and an enclosed observation deck were added to the design. This two-storey structure was dubbed the "Sky Pod."
At this point it was suggested that the tourists visiting the observation decks could make use of a restaurant facility, and then CN brass added a licenced lounge and conference area where they envisioned board meetings held atop the city. This being the 1970s, the lounge actually became a disco for several years called "Sparkles." I'll let you imagine the polyesther leasure suits and mirror balls for yourself.
CN Tower under construction in 1974
After broadcast facilities and utility areas were added, the design of the SkyPod had grown to seven decks, weighing 318 tonnes. Unlike the Ostankino Tower, the decks of the CN Tower were not made of poured concrete, but rather more typical building materials fixed to a steel skeleton. During construction, this material had to be hoisted up the sides of the central concrete shaft using 45 hydraulic jacks and miles of steel cable.
The seven-storey SkyPod with white radon "donut" housing microwave antennas
At this juncture one of the engineers suggested that visitors would pay extra to visit the highest observation deck in the world, and the construction costs were not prohibitive to modify the maintenance shaft and elevator intended to reach the main antenna in order to accommodate tourists. Thus, the SpacePod was added to the design in early 1972.
As these modifications would prevent the main antenna from being fixed to the side of the central concrete hexagon without long struts that would be prone to high winds, it was decided that a sturdier antenna would be afixed
on top, rather than from the sides of this podium at the 1,487-foot level.
The new configuration raised the height of the structure from 1,518 feet to 1,682 feet.
This was just
ninety feet shorter than the Ostankino Tower in Moscow completed five years earlier.
At this point, the Feverish Flux question from an above post was answered with:
Let's go for it!
With a few minor adjustments to the design— a few feet here and six feet there — the CN Tower could beat the Soviet tower with room to spare.
And thus the final design of the CN Tower adopted in late 1972 would make it the tallest freestanding structure in the world.
When completed in 1976, the CN Tower stood 1,815 feet... and five inches.
The CN Tower seen from the west near sundown
Status: Canadian National Railways sold the CN Tower in 1997 when the former crown corporation went public, and all operations not directly related to freight shipping were sold off.
The initials "CN" now stand for
Canada's National in order to preserve the name regardless of current ownership. In 1995, the CN Tower was declared one of the modern Seven Wonders of the World by the American Society of Civil Engineers.
The other six structures on the list were the Channel Tunnel, Empire State Building, Golden Gate Bridge, the Itaipu Dam of Brazil, the Delta Works of the Netherlands and the Panama Canal.