April 2, 1975 - Construction of the World’s Tallest Structure is completed

On this day in engineering history, construction of the world's tallest tower, the CN Tower in Toronto, Canada, was completed. Standing at a height of 1,815 feet and 5 inches, the CN tower, built by the Canadian National Railway, is Canada's National Tower and an important telecommunications hub. It has 181 stories and is the world's tallest building and free-standing structure.

Though now a major tourist attraction and symbol of the city of Toronto, the CN Tower was originally conceived as a TV and radio communications platform to serve the Toronto area. During the 1960s, construction in Toronto transformed a skyline once characterized by relatively low buildings into one dotted with skyscrapers. These new, taller buildings caused serious communication problems for the city. The CN Tower has microwave receptors at both its 1,109 ft. and 1,815 ft., 5 inches antennas, solving the communications problem. Broadcast facilities from the tower include UHF, VHF television, FM radio, microwave transmissions and fixed mobile systems.

Construction on the CN Tower began on February 6, 1973 and took 40 months to complete. The tower itself was completed on February 22, 1974, but the antenna was not completed until April 2, 1975. At its base, the CN Tower has a circumference of 385 feet. With a total weight of 130,000 tons, it contains 53,000 cubic yards of concrete, 80 miles of tensioned steel, 5,000 tons of reinforcing steel, and 600 tons of structural steel. The glass-enclosed observation elevators that run up the sides of the tower were installed by the Otis Elevator company.

The CN Tower has two main observation decks: the lower and larger SkyPod at 1,150 feet or 113 stories; and the higher but smaller Space Deck, the world's highest public observation deck, at 1,465 feet or 146 stories. The floor of the SkyPod is glass, the first of its kind in the world. Though only 2.5 inches thick, this glass floor is rated to hold 85,000 lbs.

Today, the CN Tower attracts more than 2 million visitors each year and is Canada's most recognizable icon.

http://www.cntower.ca

http://www.torontoplace.com/attractions/CNtower.htm

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http://www.toronto.com/attractions/listing/000-100-157