CN Tower- March 2008

The Antenna

Once the pouring of the concrete was completed on February 22, 1974, the final stages of building the world's tallest Tower were about to begin.

The last thing to be added to the Tower was the 102 metre (335 foot) steel broadcasting antenna, consisting of 44 pieces - the heaviest weighing 7.26 metric tonnes (8 tons).

Before the antenna could be lifted, however, the giant crane used for four years of round-the-clock service to build the Tower would have to be dismantled and brought down.

To do all this moving, "Olga" - a 10 ton Sikorsky helicopter used primarily for industrial lifting - was flown to Toronto.

And on her first trip, tragedy almost struck.

As Olga was removing the first piece of the boom, the crane lurched, twisting and seizing the supporting bolts.

Now hovering about 1500 feet up, Olga was basically attached to the Tower, with 50 minutes of fuel (the job was supposed to take only 12 minutes). The crane couldn't just be released, either. The operator was still inside.

Steel workers scrambled up and burned off the bolts, finally releasing the crane from the Tower.

Olga landed with about 14 minutes of fuel left.

After this brush with danger Olga performed the rest of the work flawlessly.
As each piece of antenna was raised, workers would stand at the top and help manoeuvre the new piece and bolt into place. And all this where the Tower is only 5 feet in diameter and with gusting winds and freezing temperatures.

It took more than 3 1/2 weeks before the final piece of antenna was secured by high rigger Paul Mitchell on April 2, 1975.

He even danced a little jig to celebrate. 1815 feet above the earth.

Today, the antenna broadcasts over 30 Toronto television and FM radio signals across Southern Ontario in addition to wireless paging and cellular telephone signals.

But more importantly to us, the antenna makes us the tallest tower on the planet.

Defining the Toronto skyline, the CN Tower is Canada’s most recognizable and celebrated icon. At a height of 553.33m (1,815 ft., 5 inches), it is the World’s Tallest Tower, a Wonder of the Modern World, an important telecommunications hub, the centre of tourism in Toronto and a first class dining and event centre. Each year, approximately 2 million people visit the Canada’s Wonder of the World to take in the breathtaking view and enjoy all of the attractions the CN Tower has to offer.

After 40 months of construction, the CN Tower was opened to the public on June 26, 1976 and it was well on its way to becoming the country’s most celebrated landmark. It is the centre of telecommunications for Toronto serving 16 Canadian television and FM radio stations, the workplace of 550 people throughout the year, and one of Toronto’s premier entertainment destinations.

Although the CN Tower inspires a sense of pride and inspiration for Canadians and a sense of awe for foreign tourists, its origins are rooted in practicality. The 1960s ushered in an unprecedented construction boom in Toronto transforming a skyline characterized by relatively low buildings into one dotted with skyscrapers. These buildings caused serious communications problems for existing transmission towers, which were simply not high enough to broadcast over the new buildings. Signals bounced off the buildings creating poor television and radio reception for residents. With its microwave receptors at 338 m (1,109 ft.) and at the 553.33m (1,815 ft., 5 inches) antenna, the CN Tower swiftly solved the communications problems with room to spare and as a result, people living in the Toronto area now enjoy some of the clearest reception in North America.

A Symbol of Strength

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 Russian 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. Ross McWhirter, editor of the Guinness Book of World Records, was on hand to record the milestone for history and since then, the CN Tower has received numerous mentions in the famous book including the World’s Longest Metal Staircase and most recently, the World’s Highest Wine Cellar. In 1996, the CN Tower’s classification was officially changed and currently holds the title the World’s Tallest Building.

In 1995, the CN Tower was classified as one of the Seven Wonders of the Modern World by the American Society of Civil Engineers. The World’s Tallest Building shares this designation with the Empire State Building, the Chunnel under the English Channel, the Golden Gate Bridge in San Francisco, Itaipu Dam on the Brazil/Paraguay border, the Panama Canal, and the North Sea Protection Works off the European coast.

Since the CN Tower opened, Canadians and tourists from around the world have made the trip to Toronto to celebrate this marvel of civil engineering. Besides serving as a telecommunications hub, the CN Tower provides world-class entertainment and a wide range of unique attractions, exhibits and food and beverage venues.

In recent years, the CN Tower has supported its vision of Toronto’s premier entertainment destination by totally renovating and redesigning 360 The Restaurant at the CN Tower, building the World’s Highest Wine Cellar, adding two new elevators, replacing the Radome and installing a $2 million leading edge security system.

Since 1997, $40 million has been invested in expanding and revitalizing the CN Tower. Local, domestic and international guests of all ages now have more to see and do as they venture through dynamic multimedia experiences, entertainment attractions and innovative food and shopping marketplaces before rocketing to the top of the Canada’s Wonder of the World.

In June 2001 the CN Tower celebrated its 25th anniversary as an engineering triumph, a symbol of pride, a critical telecommunications link and a world class entertainment and dining facility. A special event honoured the people who designed and built Canada’s Wonder of the World. The event was attended by various dignitaries including Toronto’s Mayor who declared the day “CN Tower Day” and unveiled a heritage plaque. Proceeds from a special anniversary admission were contributed to the aspiring athletes of the Canadian Olympic Association.