How was Canada's CN Tower built and what materials were used to construct it?

by Kim Siever on April 15th, 2005

The CN Tower was built in 1976 by Canadian National who wanted to demonstrate the strength of Canadian industry by building a tower taller than any other in the world. Building the CN Tower was a vast and ambitious project that involved 1,537 workers who worked 24 hours a day, five days a week for 40 months to completion.

Tower construction crews moved in on February 6, 1973, and started to remove over 56 metric tonnes of earth and shale for the foundation. Once the foundation was ready, work began on the CN Tower�s 335 m (1,100ft.) concrete shaft, a hexagonal core with three curved support arms. This 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.

Eight months later, the CN Tower�s concrete shaft was the tallest structure in Toronto and by February 1974, it was the tallest in Canada. In August 1974, work began on the seven-story tower sphere that would eventually house the observation decks and revolving restaurant. The CN Tower approached completion in March 1975, when Olga, the giant Sikorsky helicopter flew into the city to lift the 44 pieces of the antenna into place. The CN Tower was finished on April 2, 1975, and opened to the public June 26, 1976.

When the 44th and final piece of the CN Tower�s antenna was bolted into place April 2, 1975, the CN Tower joined the ranks of 17 other great structures that had previously held the title of World�s Tallest Free-Standing Structure.

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