Next – 100-Story Buildings (Apr, 1931)
Next – 100-Story Buildings
by BEVERLY BARNES
Buildings rising two hundred stories into the air are now within the realm of possibility, but with the present limitations they would be mere towers housing elevator shafts. Ingenious methods of vertical transportation, such as placing two elevators in one shaft as described below, may make the sky the limit.
HUNDRED story buildings, dwarfing the 88 story Empire State building, now rising on the site of the old Waldorf-Astoria Hotel, are visioned as a reality in the near future by business men of New York.
To make that vision possible they have petitioned the city to amend the building code to permit elevators to travel at 1400 feet per minute, instead of 700 feet, the present limit, and to permit double deck elevators or two separate elevators in one shaft.
Curiously enough the elevator, a comparatively modern invention, is the only limiting factor on how high a building may go. Solve the elevator question and 100 or even 200 story buildings are quite possible. The trouble is to get an elevator system that will be fast enough to move the traffic and will not take up so much valuable space as not -to leave enough rentable area to earn a respectable income on the investment.
If you want some idea of how much space the elevator’s of a modern skyscraper take up, look at the ground plan of the Empire State, the 1243-foot super-skyscraper rising under the guidance of former governor Al Smith. The huge pile has a frontage of 197 feet 5 inches on Fifth avenue and 424 feet 9Vk inches on 33rd and 34th streets, occupying the entire block between them. But virtually one-fourth of all that ground area is taken up by the elevator banks and their hallways. Of course, as the building ascends, the shorter shafts, locals and lower express banks, come to an end, but the building set-backs also reduce the available renting area in more than equal proportion.
It will take sixty-six elevators to serve the world’s tallest man-made structure—sixty-seven when the elevator is installed in the dirigible mooring mast on the roof, a mast whose tip will be 243 feet higher than the famed Eiffel tower in Paris. Eleven of them, ten passenger express cars and one freight, will rise as high as the 80th floor, the ten express cars traveling 951 feet, while the freight elevator, which descends into the sub-basement as well, will have a vertical rise of 981 feet. The upper tower floors, from the 79th to the 86th inclusive, will be served by local cars.
There are fifty-eight passenger cars in the various express and local banks at the ground level, and two cars in the tower shafts. All the ground level cars are designed to travel at the maximum speed now allowed—700 feet per minute—but provision is made in their mechanism to speed them up when and if the law is changed. If that happens the ten traveling express to the 66th floor and local from there to the 80th level will move at 1200 feet per minute. Eighteen serving the floors between 24 and 43 and 41 and 57 will be speeded up to 1000 feet per minute, and another eighteen to 800 feet. Only four locals, serving floors from the first to the seventh, will continue at the 700 foot speed.
The suggestion of the New York business men that two story elevators, serving two floors at the same time, and two elevators in one shaft be permitted opens up a whole new field of vertical high speed travel. No two deck passenger elevator has yet been built, though two and even three deck freight elevators have been built for garages. And two cars have never been hung in the same shaft. The nearest approach to that is in the Tribune Tower in Chicago where a tower elevator operates directly over a local car, but the local stops at the twelfth floor level and the tower car starts at the 23rd, while the space in between is not an open shaft, but is occupied by offices.
Elevator men have considered several plans for two cars in one shaft. One is to put a pit and safety buffer beneath a tower car, with a machinery floor and sub-floor below for the head of the local shaft. Considerable space would be lost, at least three floor levels, but express cars traveling without stop to the height of the local car shaft, could then deliver passengers to the three or four floors above, and finally transfer the balance to the tower car, which would not have to make the long run down to the ground, and so could better serve the tower floors.
Another idea which the elevator builders are considering is two cars in one shaft, moving independently of each other, but both going all the way down to the ground. That sounds impossible, but, as the elevator builders visualize it, it is quite practical. The upper car would be hung in the usual way, with supporting cables descending down the center of the shaft. The lower car would be hung to a cross beam, supported by cables traveling down each side of the shaft. The local would descend to the basement, while the express stopped at the ground floor to discharge and take on passengers. As the express started upward the local would ascend to the ground, load, and then follow. Coming down the process would be reversed. Safety devices preventing the cars getting too close together •or the express car coming down when the local is going up, would be necessary, but they present no particular obstacle. If any city authorizes two cars in one shaft the elevator designers are ready to produce them.
An elevator system of this sort, with two cars running independently of each other in the same shaft, has actually been built and is in operation in the plant of the Westinghouse Electric Manufacturing Company at East Pittsburgh, where it is demonstrated to prospective builders of new skyscrapers. The installation is remarkable not only because two cars run up and down in one shaft, but because the cars are built entirely of aluminum— even to the cross-head beams—with side wall panels of micarta, a lightweight synthetic material used in making airplane propellers.
Safety devices keep the two cars from approaching closer than two floors apart, and also prevent them running toward each other. The ex- press loads at the main floor and starts up, whereupon the local follows it, loads at the same floor, and continues upward. The arrangement is particularly useful in tall buildings, as the division line between express and local service can be shifted up and down to meet customer demand. If there is unusually heavy business, say, between the 20th and 30th floors of a 40 story building the local cars, which normally would operate only to the 20th floor, can extend their runs to the 30th, so that both cars would serve that section until the peak load period had passed.
The double deck car offers problems that are perhaps more serious. One car would stop only at floors with even numbers and the other at floors with odd numbers. A passenger getting on at one level and wishing to get off at the other either would have to transfer somewhere en route, and walk up or down one floor, or get off one floor before or beyond his destination, and take the stairs. There would be an operator in each car, but the controls would be interlocked so that neither could start the car until the other was ready. And, finally, all floor levels in the building would have to be exactly the same distance apart.
Elevators have developed in the last few years to where they are not only almost human, but in some cases are even better than human operators could be. It was human faults that produced the modern signal control system in which the operator punches buttons before he starts for all the floors where passengers wish to alight, and from there on has nothing to do but close the doors and start the car. It stops and the doors open automatically, and it not only stops for the passengers who want off, but automatically stops to pick up those who want on.
The signal system owes its being largely to the fact that human operators could not think fast enough and make their muscles respond quick enough to catch signals and stop a car moving at 700 feet a minute. With the multi-volt gearless car and the signal system the operator has very little to do, beyond seeing that passengers get off and on safely. Instead of the old fashioned worm gear drive of the hoisting drum, the drum is built right on the armature shaft of the motor. Regardless of the type of electric current available, the hoisting motor gets its power from its own motor generator set, and therein lies its secret, for the voltage can be varied at will. When the operator in the car, or a waiting passenger at a floor, presses the signal button, a selector sets up the necessary contacts on a panel at the head of the shaft. Attached to the elevator car is a steel tape, running over a driving gear which in turn is belted to a screw moving the cross-head of the selector—virtually a small elevator. As the car travels up and down the shaft the cross head moves correspondingly, and establishes the contacts which slow down, stop and start the car. As the car approaches a stop the controller cuts out the driving current and cuts in the micro-drive, which, sending a reduced voltage through the driving motor, brings the car to a smooth stop exactly at the floor level.
Elevator counterbalances are heavier than the car, by about forty per cent of the maximum load the car may carry. As a result an empty car is lighter than the counterbalance, and a heavily loaded one is heavier, and so each tries to run faster than the governor speed, the empty one when going up and the loaded one when coming down. When that happens the driving motor becomes a generator, and actually puts current back into the line, while the enormous resistance of the field acts as a brake and maintains an even speed, just as regeneration is used to brake heavy trains on the electrified mountain divisions of the Milwaukee Road, where air brakes are never necessary to keep the train speed constant while going down hill.
Modern elevators are provided with so many safety features that accidents are virtually impossible. A single cable is sufficient to support the load, yet six are commonly used, not so much for safety as to give more traction on the hoisting drum. A ball governor fixes the limiting speed, and in event of accident would trip a clutch, releasing dogs and shoes which would press against the guide rails and bring the car to a stop. In the pit at the bottom of the shaft an oil piston buffer provides additional safety, and the counterbalance also is fitted with a buffer. The stops at the ends, or terminals of the elevator “line” are operated by curved cam rails attached to the guides. The cams move a lever which trips the switches and brings the car to a stop. That’s just added insurance against failure of the selector, and then to guard against failure of the cam lever there’s a final limiting switch which cuts out all current and stops everything.
It’s a long step from the first crude elevator built by Henry Waterman in New York in 1850 to such super-human machines. That first elevator was simply a platform hoist, built to operate between two floors. The first passenger elevator ever installed was built by Elisha Graves Otis, of Yonkers, N. Y., in 1852, and in 1854 he invented the first elevator safety device, designed to prevent the car falling if the hoisting rope should break. Otis Tufts, of Boston, invented the “vertical railway” in 1859, a platform raised and lowered by a huge screw, but only two were ever built. The Otis organization invented an oscillating cylinder steam engine and a stationary cylinder engine, both of which were in general use for elevators until the hydraulic type was introduced in the seventies.