Saturday, February 14, 2009

Mississauga and Toronto Residents are blessed to have the CN Tower

This was a very interesting article about the CN Tower that was forwarded to me from a friend. I thought I would share it with you as millions of people from Mississauga and Toronto drive by the CN Tower and probably don't give it a moments thought anymore.

It's a fabulous achievement in engineering and construction and should always be looked upon as a great achievement for the GTA.




The reason for them dates back to what was probably emerging man's first intelligent perception - that the sun gives life. Through the entire span of known and unknown history, man has been driven by a primal urge to reach ever higher for the sky above. We build upward, reaching for the heavens when erecting a place to worship or building monuments to our prophets or, more recently, celebrating our mastery over the environment.

Man's upward reach has been limited by the materials he has available and the techniques he uses to manipulate them. Thus, the oldest surviving tall structures in the world are the pyramids of the Pharaohs of Egypt, who were revered as gods, or at least prophets on speaking terms with the gods. How these edifices were built remains a mystery locked forever in the past, but one thing seems clear: the Pharaohs played a stupendous status game, each one trying to build higher than the other as proof of his greater importance. (Much the same game, in fact, as several Canadian banks have played in downtown Toronto; each one is trying to top the other with a taller skyscraper.) At the time of its completion, each of the buildings and structures illustrated above was the tallest in the world.


Building the tallest tower in the world produced unique construction and engineering problems, revolutionary solutions and a seemingly inexhaustible list of "the most..the biggest...the highest...the first..." But perhaps the most significant "first" was the technique devised to actually put up the concrete section of the tower. A 400-ton mould of the structure was built of wood and steel and in a round-the-clock operation, concrete mixed on the site was poured inside the mould as it moved, slowly but continuously, skyward. The tapering shape of the tower was created by reducing the size of the mould as it moved upwards. Tower construction began in the fall of 1972 when a drill rig trundled onto the John Street site and bored 300 feet down into the gray Dundas shale that supports most of Toronto. In February 1973, the earth moving behemoths of the modern construction industry arrived. More than 62,000 tons of earth and rock were removed in digging the main, 50-foot deep hole. Then, 18,000 tons of concrete and 500 tons of reinforcing steel were used to build the 22-foot thick foundation.


The seven-story building 1,100 feet above ground houses the microwave equipment on the lower floor, while the next three floors are open to the public, including an enclosed observation deck, a partially opened one, and the revolving restaurant. The top three floors are devoted to television transmitters, FM transmitters and, on the seventh floor, the monstrous pieces of mechanical equipment needed to power everything.


The 420-seat revolving restaurant is the world's tallest, with a diameter of 150 feet (the one at Australia square in Sydney, which is in second place, has a diameter of 122 feet) and that part of the floor that rotates has a top speed of eight feet a minute. That's so fast you might get indigestion, so it is slowed to five feet a minute for dinner, which means you can orbit the 450-foot circumference in 90 minutes. The 16-foot-wide moving platform runs on bearings so precisely designed that it is driven by one 2 hp electric motor, with a second as a spare. And if both break down, two strong men can push it.


Originally, there were supposed to be a cluster of three separate antennas on top of the concrete tower. Had this plan been adopted, it is possible that the total height of the structure would not have topped that of the 1,761.89-foot-high Ostankino Tower in Moscow. Ultimately, however, communications engineers decided the most efficient design was one which stacked one kind of antenna atop another to make a single antenna 350 feet high. That slender five-sided needle atop the concrete shaft has finally rid the Toronto area of the worst television and FM-radio reception of any North American city. One part of the problem was that the fairly flat countryside is dotted with high-rise apartments and offices, so TV sets usually received two signals: a strong one from the transmitters and a weaker one "bounced" from those high-rise buildings. It was this "bounce" that caused TV screen ghosting.


Four elevators zip up the sides of the tower at 1,200 feet per minute, which means you go higher quicker than when taking off in a jet plane. Each elevator has a glass wall. Each elevator could hold 22 people, but the elevators are never quite full, partly because not everyone could see and partly because passengers might feel too confined. The speed was determined by an elaborate formula for "acceleration realization threshold" (the speed at which you know you're moving), so that it's fast enough to be fun and not too fast to be frightening or to cause heart attacks, nausea or fainting fits. However, it gives just about everyone an attack of Otitis-media, or ear popping, because of pressure changes. To alleviate this, swallow at least five times in the 70-second trip.

The tower also has a stairway, used in an emergency. A physically fit person would take 20 minutes to get down the 2,570 stairs in the hexagonal core, and at least 40 minutes to climb up. When the stairway - the world's tallest made of concrete - was finished, one construction worker shucked his clothes and "streaked" the tower from top to bottom. Yet another tower record.


Lightning strikes the tower between 150 and 200 times a year, which means it is also the world's tallest free-standing lightning rod. Lightning conductors atop the tower are linked to three copper strips that run down the tower and are grounded to forty-two rods, each 20 feet long and buried 20 feet below ground.The stairs, elevator rails, window frames, sewage, water pipes and anything else that could attract lightning are linked to the copper strips. ICING Anywhere ice is likely to form - at any change in the tower contour line, or places like the roof edges of the Sky Pod - has been ice-proofed, either with heated de-icing cables or sheathed in shiny plastic to which ice cannot cling. The fiberglass surface and the shape of the transmission mast means that ice will never build up to a dangerous thickness and fall to the ground in chunks but will, instead, slide off and break itself into powder-like snow almost as soon as it's formed.


Don't expect to get a steak flambéed at table side at the revolving restaurant. The fire department has forbidden open flame cooking up in the tower. In fact, the planners and the fire marshal have gone to extraordinary lengths to make the tower fireproof. Each steel floor has a coating of a fire-resistant mineral fibre, and all furnishings are as fireproof as any furniture can be. The main kitchens, where open-flame cooking is permitted, are in the basement. Also located there are the emergency fire pumps than can each squirt water to the top of the tower at the rate of 500 gallons a minute. A sprinkler system is located everywhere. Since electrical transformers have been known to explode into flames, the seven installed in the tower are immersed in a non-flammable fluid instead of the customary oil.


Unlike a jumbo jet that moves mostly through the upper "smooth" layers of air and is grounded in bad weather, the CN Tower must survive turbulent, treacherous winds and was built to withstand twice as strong a wind as Toronto will ever see. Weather records show 114 mph as the top wind speed in the last century. The tower was built to withstand a wind of 160 mph. At 110 mph, a wind exerts 60 pounds of pressure where it hits windows in the accommodation pod. At the sides, it exerts a 60-pound negative pressure. So experts designed windows that can withstand 120 pounds of either kind of stress. The outside pane is three-eighths of an inch thick tempered glass, the inside pane is half an inch thick. The main concrete tower - 53,000 cubic yards of concrete "tied" together with 80 miles of steel cable - would only wobble 10 inches from side to side, and the movement would be so slow you wouldn't even notice a change in the level of the champagne in your glass (that is, presuming you'd been stupid enough to go out to dinner in such weather in the first place).


CN Tower Limited decided it was vital that the $52 million tower be an ultimate tourist attraction in order to ensure it was self-supporting financially, as well as structurally. The tower has become a North American landmark and a tourist attraction unrivaled in Ontario, perhaps even Canada, other than Niagara Falls. At the base of the tower, past the gardens and the fountains and pools, is a unique shop specializing in CN Tower souvenirs and Canadiana which, at one time, included the souvenir medals and medals used for keychains and necklaces struck by Interbranch International Mint. The elevator ride is in itself super-spectacular. Short of piloting a jet fighter, there's nowhere else in the world you can climb so high so fast, and the main observation decks in the Sky Pod are so high you have the uncanny feeling you're looking down on the world from a plane. On those decks are six telescopes with 20.1 zoom lenses, which means that by operating the controls you can magnify what you see with the naked eye from 10 to 200 times. But for many, the greatest attraction is the view from The Space Deck observation platform. There's nothing further up but the antenna and the sky. The observation deck has floor-to-ceiling windows that lean outwards so that you feel as though you are perched on the edge of..well, nothing.


The tower weighs 130,000 tons, which is twice as heavy as the world's biggest luxury liner and about the same weight as 23,214 large elephants.

Fifty-three thousand cubic yards of concrete were poured to build the tower - and that's enough to build a concrete curb along the 401 from Toronto to Kingston, 150 miles away.

The tower has the longest concrete staircase in the world. It has 2,570 steps.

Even the lower observation platforms are so high that you can see south to Rochester, New York and the far shore of Lake Simcoe to the north.

You can also see the eternal cloud of spray that looms over Niagara Falls.

The elevators up to the Sky Pod are capable of carrying 30,000 people a day, or 10,950,000 a year, counting Sundays and Christmas Day. At that rate, however, the place gets a bit crowded.

Between the Sky Pod and the uppermost observation platform there is a special shuttle elevator.

It takes you up to the 1,450 foot level, which makes it the highest elevator ride in the world.

There is a fee charged to take the elevator to the observation decks, except when you are going up to the revolving restaurant for dinner and you have made an advance reservation.

The CN Tower's souvenir shop ran out of the souvenir medals ordered from Interbranch International Mint at least 20 years ago.

No comments:

Post a Comment