Amazing Engineering – CN Tower

Amazing Engineering is an introduction to the Seven Wonders of the Modern World, a list of modern engineering marvels compiled by the American Society of Engineers (ASCE):

In the first installment, we learned a little bit about the Golden Gate Bridge in San Francisco, California. In part two, we traveled out of the United States to northwestern Europe to learn about the Netherlands North Sea Protection Works. After that, we headed to South America where we learned about the Itaipu Dam on the borders of Brazil and Paraguay. Today, we learn about the CN Tower in Toronto, Ontario. Completed in 1976, it held the record for the world’s tallest freestanding structure and world’s tallest tower for 34 years!

During the late 1960s and early 1970s, Toronto was growing at a rapid pace. The growth in population and businesses prompted the building of multiple skyscrapers in the downtown area. While this growth was good for the city, it was not good for television and radio reception.

To remedy this problem, Canadian National Railway began plans for a large radio and communications tower which would not only bring better airways transmissions to the people of Toronto, but it would show the world “the strength of the Canadian industry.”


A photo posted by CN Tower (@cntower) on

The project became official in 1972, and construction officially began on February 6, 1973. After excavation, the base of the structure took four months to build, incorporating 7,000 m3 of concrete! The tower was designed to have a concrete shaft consisting of a hexagonal core with three curved support arms.

[Construction of the concrete shaft] involved pouring concrete into a massive mold or “slipform”. As the concrete hardened, the slipform, supported by a ring of climbing jacks powered by hydraulic pressure, moved upwards, gradually decreasing in size to produce the CN Tower’s gracefully tapered contour. –CN Tower

As engineers tested the bedrock soil at the build site, they realized that they would have the potential to make the CN Tower high enough to claim the title of the the tallest building in the world. As they went forward with design plans, any changes that were made kept this goal in mind. They would have to be careful with a project of this magnitude, however. All concrete used would have to come from the same source, so it was all mixed on site before being poured. Once the foundation and concrete shaft were constructed, the Tower would be completed with a seven-story sphere that had room for observation decks and a restaurant.

A photo posted by CN Tower (@cntower) on

The final piece of the CN Tower was the antenna. Originally, the installation plans would have taken workers six months to complete this phase of the project with a crane. However, during construction engineers were able to procure use of a Sikorsky S-64 Skycrane helicopter, which was previously used by the United States Army. Instead of six months, the antenna topped the tower in only three and a half weeks!

With a final construction cost of roughly CDN $63 million, the Tower opened to the public on June 26, 1976. It held the world record for the world’s tallest freestanding structure and world’s tallest tower at the same time for 34 years. However, the construction of the Burj Khalifa and Canton Tower changed this in 2010. It is now the 3rd tallest tower in the world and remains the tallest freestanding structure in the Western Hemisphere.


A photo posted by CN Tower (@cntower) on

Fun facts about the CN Tower:

  • Each year, more than 1.5 million people visit the CN Tower, which now “provides a wide range of unique attractions, exhibits and food and beverage venues”
  • The Tower has a total of six glass-fronted elevators to take visitors to the observation decks
  • The CN Tower stands at 1,815ft. 5 in. tall
  • Construction involved 1,537 workers who worked 24 hours a day, five days a week for 40 months.
  • In May 2007, a freezing rain storm resulted in thick layers of ice on the tower and surrounding buildings. Heavy winds forced police to close nearby streets as the ice began to melt to prevent injuries from the falling ice

To learn more about the CN Tower, including facts about its history and what improvements have been made over the years, check out the links below!

CN Tower

CN Tower – EdgeWalk

CN Tower – Wikipedia

CN Tower – Instagram

CN Tower – TripAdvisor

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