A Tower with Its Top in the Heavens
By “Awake!” correspondent in Canada
THERE—poised majestically in Toronto, like a giant rocket ship ready for lift-off, its needle-nosed upper end pointing skyward—is a tower that truly has its top “in the heavens”! One feels excitement as one looks with unbelieving eyes up and up to its imposing 1,815-foot elevation, five times as high as the Saturn V rocket used in the Apollo 11 moon shot. What has caught one’s gaze is the “CN Tower,” the tallest self-supporting structure in the world. (“CN” for Canadian National, the government-owned railway and communications system in Canada.)
From very early times in human history man has been occupied with building towers that ‘reach into the skies,’ first for purposes of false religion and then for military advantage. (Gen. 11:1-9) Though the earliest of these of which we have any record, a temple tower or ziggurat, did not have a noble objective, men since then have at times shown amazing abilities to achieve some worthwhile purpose with towers. Sometimes they have been erected solely for architectural beauty and symmetry, but at other times they have been designed for more practical reasons, such as in supporting huge spans in bridges.
The CN Tower strives to combine these latter goals, being both aesthetically pleasing to the eye and serving a number of practical purposes. As the federal Minister of Mines, Energy and Natural Resources, Donald McDonald, expressed it when work on the tower began: “The CN Tower will not only be impressive but will be very practical as well.”
Impressive it is! Have you seen the Eiffel Tower in Paris? Put another Eiffel Tower on top of it and the pinnacle of the CN Tower would be only about 150 feet under that doubled height. Or, have you been to the top of the Empire State Building in New York city? You were only a little more than two thirds of the way to the topmost elevation of this tower. Yes, it is almost 400 feet higher than the tallest office building in the world, the Sears Tower in Chicago, U.S.A. Though it is admitted that there are TV transmitters higher than the 1,815 feet of the CN Tower (about 553 meters), they are supported by guy wires or other external sources of stability, whereas the CN Tower is “freestanding.” More than one third of a mile high, it dominates the Metro Toronto landscape.
However, it is not just the lofty altitude of the tower that impresses. It rises from its foundation in the form of three rocketlike “fins,” this Y-shaped base tapering gracefully upward for about 1,100 feet. At this point the line of ascent is pleasingly broken by a seven-story circular observation deck/revolving restaurant complex. Above this “skypod” the ascent, blending into a hexagonal column, continues skyward for about another 400 feet to an upper observation level. Finally, a gradually tapering 335-foot antenna mast crowns the structure, bringing it to its needle-pointed tip. Once you see it, its simple, graceful form leaves an indelible picture on the mind.
An Engineering Marvel
‘How did all this mass get up there?’ you ask yourself. It was not a simple operation. After intensive testing down to as much as 90 feet in the area where the foundation is, excavations began in February 1973. They went down to around 55 feet (the last 25 feet into rock), requiring more than 62,000 tons of shale to be removed. Wet burlap was applied to the exposed surface of the pit and then a “blanket” of concrete a foot thick was laid down to avoid deterioration in the base rock. On top of that another layer of concrete was poured, this one 18 feet thick! Then came a foundation of 9,250 cubic yards of concrete.
Next was the pouring of concrete for the Y-shaped portion of the tower and its hexagonal column. This was accomplished by using a “slipform” that moved steadily upward under hydraulic pressure (held in place by a ring of climbing jacks), extruding concrete around a maze of steel bars and post-tensioned steel at the rate of about 20 feet of ascending growth each day! This pouring continued until February 22, 1974, to the 1,464-foot level, just below where the upper observation deck is located. A “topping off” ceremony was held March 21, 1974. At least 106,000 tons of concrete had been used, along with 5,000 tons of reinforcing steel, 600 tons of structural steel and 1,000 tons (80 miles!) of tensioning cable.
This unusual method of construction produced an engineering marvel. For such great heights structural engineers will allow for a variance of up to three inches from absolute vertical plumbness. Using a giant plumb bob and precision-made optical instruments for regular checks, it was possible to complete the pouring with a variance of only 1.1 inch!
Another thing that had to be checked daily was the tendency of the structure to twist as it rose from the earth. This “torsional oscillation” is said to be related to the earth’s rotation, in the northern hemisphere twisting tall, narrow structures in a counterclockwise direction during their erection. It goes the other way in the southern hemisphere. The above-mentioned instruments and some survey stations up to 1,000 feet away gave readings that allowed for any needed adjustments in the jacking system. A “true” building resulted.
On top of all of this rests the more than 300-ton antenna mast, installed by helicopter. It is planned that this steel transmission mast will have a glass-reinforced plastic radome to protect it in the winter months from accumulations of ice and snow.
Strength and Safety
Is the tower strong—and safe? Those connected with the project believe so. Great effort was made to assure strength and safety, as already seen in the foundation work and the method of strengthening the concrete. Additionally, according to Dr. R. A. Bandeen, president of CN Tower, Limited, the concrete itself has a strength of 6,000 pounds per square inch, well beyond the 5,000 pounds per square inch called for in the specifications. This is felt to be more than what is needed for safety. A staff of technicians and field engineers used an on-site laboratory for testing the quality of the concrete every day.
But, what if something like a jumbo jet rammed the tower? The answer of the tower’s analysis expert, Dr. Bruno Thurlimann of Switzerland, assured that damage to the tower would be minimal. The effect on the aircraft would be another matter.
Even in high winds the top will sway very little. Already, in a gale wind the skypod level moved only about five inches. Some researchers claim that it may move as much as twenty-four inches at that level in a hurricane-force gust. That seems a lot until you hear about reports that the Ostankino communications tower in Moscow (1,748 feet high) has swayed many feet in high winds!
The secret to the ability of the CN Tower to withstand high winds was found to be in its final design and shape. As wind-tunnel expert Dr. Alan Davenport commented after wind-testing various models of the structure: “It’s taken [many] years to discover that the shape of a tree, tapering from a broad base, is the best to withstand the wind.” Man continues to learn that created things reflect a great Intelligence.
Use and Purpose
But why build such a soaring column? Was it not an expensive undertaking if it was just to lay claim to having the world’s highest self-supporting structure? The first answer given is that it is meant to be primarily a communications tower. One reason for it is that Toronto, as all cities with a large number of skyscrapers, has a television transmission problem: double images on the TV screen due to slightly delayed waves created when their paths are affected by the high-rise buildings. It is hoped that this tower’s antenna is high enough to eliminate the bothersome “ghosting.” It is also designed so that it can increase the “reach” of some stations by 50 percent.
Indicating other communications use, Norman J. MacMillan, chairman and president of the Canadian National System, pointed out: “With its microwave facilities, the Tower will help speed the flow across Canada of all forms of vital business communication, of computer data, weather maps and information, reservation data for trains and airplanes, and even stock market reports.” Improved communications for municipal services was also mentioned by him as a benefit from the tower.
Now, all of that is the reason for the more than $3-million antenna complex at the topmost portion of the tower. It is planned that it will transmit for eight television channels and eleven FM stations.
The tower is also ideal for some forms of scientific research. It is felt that it “could help unravel some mysteries that have baffled structural engineers and environmental researchers.” CN Tower will cooperate with the University of Toronto, the National Research Council and Environment Canada on a program of instrumentation for the tower. The Toronto Star reports that some 15- and 30-foot retractable booms will spike the tower at four levels to “aid aircraft safety” and measure “wind speeds and air pollution.” It described a $200,000 program using about 100 instruments to test such things as structural stress. Instrument data will be processed by computers as readings are taken every three hours.
In addition, its planners believe that the dartlike edifice will become a major tourist attraction, a “people tower,” after its opening, scheduled now for early in 1976. The seven-level skypod of aluminum and glass will offer tourists two observation decks (one glassed in, one “outdoor” type) and a revolving dining room, all with a spectacular view—a 75-mile (120 kilometer) panorama! And there will be plenty of room: 70,000 square feet of it. The restaurant will seat 400 and the observation levels will hold another 600 people. You can reach them by one of four elevators that will ride upward in glass-fronted outside chutes, giving a thrilling view as one is lifted almost a quarter of a mile in about one minute! And if that isn’t enough, an inside elevator will take you up the rest of the column to the upper observation area at 1,500 feet.
Plans are being made for it to be the focal point of a $1.5-billion redevelopment site to be called Metro Centre. It is proposed that the present railroad tracks and roundhouses will give way to an attractive parkland and a residential/commercial development covering about 190 acres. A convention center is to be among the many facilities to be offered there. According to plans, the tower itself is to rise out of a reflecting pool situated in a landscaped area. A pedestrian bridge is to provide access to the glass-walled rotunda at the tower’s base. As to how much of all this will finally be accomplished, time will tell.
Another reason for the edifice is revenue. Of course, that is one of the more important reasons why enterprises such as this are undertaken. Though the cost of the tower will run about $30 million, its planners envision an estimated annual income of $6 million. Antenna rentals, they say, will involve more than a million dollars annually. Rent from those managing the skypod restaurant and lounge and the shops and restaurants in the rotunda is to add to the profits. With the tourists, expected to number about 2 million annually, revenues from elevator use alone would add up fast.
There is no doubt that the erection of this tower required ingenuity, innovation and conviction. Hard work, long hours, revisions and frustrations are all a part of such mammoth undertakings. Its original concept called for vision, initiative, courage—and a positive attitude. It is hoped that much that has been learned and that will yet be learned will be used for the benefit of man. The earliest of towering edifices, that temple tower at Babel, with its wrong motive, ended up producing a communications problem—a diversity of tongues. It is hoped by those connected with the CN Tower that it will improve communications and contribute to advancing human knowledge.