Why it all started
During Toronto's building boom in the early 70's, a serious problem was developing. People were experiencing poor quality television. And it wasn't just the sitcoms. The pre-skyscrapertransmission towers of Toronto stations were simply not high enough anymore.
As office buildings were reaching higher and higher, TV and radio reception began suffering from 'ghosting', or a weakening of clarity. Signals from Toronto and from Buffalo, New York were bouncing off the buildings. As a result viewers often saw a weaker station superimposed over another. In effect, they were watching two shows at once. And this was before channel surfing allowed us to do this on purpose. It became clear that what we needed was an antenna that would not only be taller than any building in the city, but one that would be taller than anything that would probably ever be built.
In 1972, Canadian National (CN) set out to build a tower that would solve the communications problems, serve as a world class entertainment destination, and achieve international recognition as the world's tallest tower.
The Tower's microwave receivers are located 338 m (1,109 ft) above the ground in the radome (the donut-shaped collar at the base of SkyPod). The important VHF, UHF and television equipment intrinsic to the Tower's purpose as a broadcast transmission facility are located here. Incoming signals are monitored and fed to the antenna for transmitting. Further up at 360 m (1,180 ft) is the centre of FM broadcasting in Toronto. CFNY, CHUM, CHFI, CKFM, Q107, CHIN, CJRT, CJEZ, CBC radio and City TV, CFTO-TV, TVO, CBLT, CFMT,
Global, CBLFT, and CICA all use the Tower's superior transmission capabilities.
The transmission equipment, although powerful, is extremely sensitive. The radome, designed to protect it from the
elements, is a teflon-coated fibreglassrayon fabric which can hold the weight of an average adult male yet measures
only 1/32 of an inch. Its balloon-like shape results from inflating the skin to five times its normal size then maintaining constant pressure.
As office buildings were reaching higher and higher, TV and radio reception began suffering from 'ghosting', or a weakening of clarity. Signals from Toronto and from Buffalo, New York were bouncing off the buildings. As a result viewers often saw a weaker station superimposed over another. In effect, they were watching two shows at once. And this was before channel surfing allowed us to do this on purpose. It became clear that what we needed was an antenna that would not only be taller than any building in the city, but one that would be taller than anything that would probably ever be built.
In 1972, Canadian National (CN) set out to build a tower that would solve the communications problems, serve as a world class entertainment destination, and achieve international recognition as the world's tallest tower.
The Tower's microwave receivers are located 338 m (1,109 ft) above the ground in the radome (the donut-shaped collar at the base of SkyPod). The important VHF, UHF and television equipment intrinsic to the Tower's purpose as a broadcast transmission facility are located here. Incoming signals are monitored and fed to the antenna for transmitting. Further up at 360 m (1,180 ft) is the centre of FM broadcasting in Toronto. CFNY, CHUM, CHFI, CKFM, Q107, CHIN, CJRT, CJEZ, CBC radio and City TV, CFTO-TV, TVO, CBLT, CFMT,
Global, CBLFT, and CICA all use the Tower's superior transmission capabilities.
The transmission equipment, although powerful, is extremely sensitive. The radome, designed to protect it from the
elements, is a teflon-coated fibreglassrayon fabric which can hold the weight of an average adult male yet measures
only 1/32 of an inch. Its balloon-like shape results from inflating the skin to five times its normal size then maintaining constant pressure.
Tower Construction
When engineers started to plan the foundation of the CN Tower, they were breaking new ground in more ways than one. Never before had anyone been faced with the task of designing a base so far into the ground and they came up against many construction challenges unique to this project.
After an elaborate series of tests on the soil to assess the condition of the bedrock and determine how it would react to changes in hydrostatic pressure, the work was ready to begin. On February 6, 1973, hundreds of people, engaged in a historic enterprise, moved
in and started to carve out the launching pad for the World's Tallest Building. They removed 56,234 metric tonnes (62,000 tons) of earth and shale before pouring a thick concrete and steel foundation 6.71 m (22 ft) deep on a base of hand-and-machine-smoothed shale.
Supporting the World's Tallest Building is a tall order and by the time it was finished the y-shaped foundation contained 7,046 cubic metres (9,200 cubic yards) of concrete, 453.5 metric tonnes (500 tons) of reinforcing steel and 36.28 metric tonnes (40 tons) of thick,
tensioning cables. The thoroughness and speed with which the foundation was laid is noteworthy. The complete foundation was in place just four months after the first spade of earth had been turned.
Once the foundation was ready, work began on the Tower's 335 m (1,100ft) concrete shaft a hexagonal core with three curved support arms. 1,537 people worked round the clock for 40 months to pour the concrete and raise the Tower inch by inch. 24 hours a day, five days a week, concrete was poured 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 Tower's gracefully tapered contour. When the slipform was completed on February 22, 1974, it had become the tallest building in Canada.
In August of 1974, workers began building, the Towers crowning glory, the SkyPod, a seven-storey building that would eventually house two observation decks, 36O Revolving Restaurant, Horizons, the GLASS FLOOR and various technical areas. This construction in the sky involved lifting 318 metric tons of steel and wood brackets up the sides of the Tower using 45 hydraulic jacks and miles of steel cable. To build the observation level, workers bolted brackets to tensioned steel bars and placed concrete in the wooden frames, then placed a three-feet high compression ring around the outside.
Creating the two-storey Space Deck, the World's Highest Public Observation Gallery, involved Cantilevering a concrete platform around the top edge of the Tower. A glass wall was suspended from the overhang of its roof, banking inwards at the bottom and completely enclosing the upper storey.
When the concrete part of the Tower was completed, Torontonians bid farewell to the familiar CN Tower crane which had worked tirelessly for almost four years. But its replacement was equally impressive--Olga, the giant Russian Sikorsky helicopter commissioned to assemble the Tower's antenna, the slim, stacked broadcasting receptor rising 350 feet from the shaft. Before it could start lifting pieces of the antenna into the sky, the helicopter dismantled the crane in eight sections. After that, Olga lifted the 36 pieces of the antenna into place with remarkable precision. As the helicopter raised each piece of the antenna, fearless workers
helped manoeuvre and bolt the new piece into place in gusting winds and freezing temperatures. Amazingly, the entire operation lasted only 3 1/2 weeks and by the end, 0lga had executed 55 lifts.
After an elaborate series of tests on the soil to assess the condition of the bedrock and determine how it would react to changes in hydrostatic pressure, the work was ready to begin. On February 6, 1973, hundreds of people, engaged in a historic enterprise, moved
in and started to carve out the launching pad for the World's Tallest Building. They removed 56,234 metric tonnes (62,000 tons) of earth and shale before pouring a thick concrete and steel foundation 6.71 m (22 ft) deep on a base of hand-and-machine-smoothed shale.
Supporting the World's Tallest Building is a tall order and by the time it was finished the y-shaped foundation contained 7,046 cubic metres (9,200 cubic yards) of concrete, 453.5 metric tonnes (500 tons) of reinforcing steel and 36.28 metric tonnes (40 tons) of thick,
tensioning cables. The thoroughness and speed with which the foundation was laid is noteworthy. The complete foundation was in place just four months after the first spade of earth had been turned.
Once the foundation was ready, work began on the Tower's 335 m (1,100ft) concrete shaft a hexagonal core with three curved support arms. 1,537 people worked round the clock for 40 months to pour the concrete and raise the Tower inch by inch. 24 hours a day, five days a week, concrete was poured 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 Tower's gracefully tapered contour. When the slipform was completed on February 22, 1974, it had become the tallest building in Canada.
In August of 1974, workers began building, the Towers crowning glory, the SkyPod, a seven-storey building that would eventually house two observation decks, 36O Revolving Restaurant, Horizons, the GLASS FLOOR and various technical areas. This construction in the sky involved lifting 318 metric tons of steel and wood brackets up the sides of the Tower using 45 hydraulic jacks and miles of steel cable. To build the observation level, workers bolted brackets to tensioned steel bars and placed concrete in the wooden frames, then placed a three-feet high compression ring around the outside.
Creating the two-storey Space Deck, the World's Highest Public Observation Gallery, involved Cantilevering a concrete platform around the top edge of the Tower. A glass wall was suspended from the overhang of its roof, banking inwards at the bottom and completely enclosing the upper storey.
When the concrete part of the Tower was completed, Torontonians bid farewell to the familiar CN Tower crane which had worked tirelessly for almost four years. But its replacement was equally impressive--Olga, the giant Russian Sikorsky helicopter commissioned to assemble the Tower's antenna, the slim, stacked broadcasting receptor rising 350 feet from the shaft. Before it could start lifting pieces of the antenna into the sky, the helicopter dismantled the crane in eight sections. After that, Olga lifted the 36 pieces of the antenna into place with remarkable precision. As the helicopter raised each piece of the antenna, fearless workers
helped manoeuvre and bolt the new piece into place in gusting winds and freezing temperatures. Amazingly, the entire operation lasted only 3 1/2 weeks and by the end, 0lga had executed 55 lifts.
The Tower Today
Each year about 1.6 million people visit the CN Tower and they are whisked to the SkyPod by high-speed elevators in just 58 seconds. In March, 1997, the Tower improved this service by introducing two new elevators providing not only an increased passenger capacity of 1,600 people an hour, but also a brand new view of downtown.
The CN Tower’s latest attraction, EdgeWalk, takes thrill seekers to new heights today. The first of its kind in North America, EdgeWalk is the world’s highest full circle hands-free walk encircling the top of the CN Tower’s main pod, 356 metres, (1168 feet, 116 stories) above the ground. The half-hour experience, which includes re-admission into the CN Tower’s other attractions (Look Out, Glass Floor, Sky Pod Levels, movie and ride) costs $175.