  A great part of the Eiffel Tower’s worth and its raison d’Être lay in the overwhelming visual power by which it was to symbolize to a world audience the scientific, artistic, and, above all, the technical achievements of the French Republic. Another consideration, in Eiffel’s opinion, was its great potential value as a scientific observatory. At its summit grand experiments and observations would be possible in such fields as meteorology and astronomy. In this respect it was welcomed as a tremendous improvement over the balloon and steam winch that had been featured in this service at the 1878 Paris exposition. Experiments were also to be conducted on the electrical illumination of cities from great heights. The great strategic value of the Tower as an observation post also was recognized. But from the beginning, sight was never lost of the structure’s great value as an unprecedented public attraction, and its systematic exploitation in this manner played a part in its planning, second perhaps only to the basic design. Larger Image Figure 22.—Various levels of the Eiffel Tower. (Adapted from Gustave Eiffel, La Tour de Trois Cents MÈtres, Paris, 1900, pl. 1.) The conveyance of multitudes of visitors to the Tower’s first or main platform and a somewhat lesser number to the summit was a technical problem whose seriousness Eiffel must certainly have been aware of at the project’s onset. While a few visitors could be expected to walk to the first or possibly second stage, 377 feet above the ground, the main means of transport obviously had to be elevators. Indeed, the two aspects of the Tower with which the Exposition commissioners were most deeply concerned were the adequate grounding of lightning and the provision of a reliable system of elevators, which they insisted be unconditionally safe. To study the elevator problem, Eiffel retained a man named Backmann who was considered an expert on the subject. Apparently Backmann originally was to design the complete system, but he was to prove inadequate to the task. As his few schemes are The Backmann design for the upper elevators was based upon a principle which had been attractive to many inventors in the mid-19th century period of elevator development—that of “screwing the car up” by means of a threaded element and a nut, either of which might be rotated and the other remain stationary. The analogy to a nut and bolt made the scheme an obvious one at that early time, but its inherent complexity soon became equally evident and it never achieved practical success. Backmann projected two cylindrical cars that traveled in parallel shafts and balanced one another from opposite ends of common cables that passed over a sheave in the upperworks. Around the inside of each shaft extended a spiral track upon which ran rollers attached to revolving frames underneath the cars. When the frames were made to revolve, the rollers, running around the track, would raise or lower one car, the other traveling in the opposite direction (fig. 23). In the plan as first presented, a ground-based steam engine drove the frames and rollers through an endless fly rope—traveling at high speed presumably to permit it to be of small diameter and still transmit a reasonable amount of power—which engaged pulleys on the cars. The design was remarkably similar to that of the Miller Patent Screw Hoisting Machine, which had had a brief life in the United States around 1865. The Miller system (see p. 19) used a flat belt rather than a rope (fig. 20). This plan was quickly rejected, probably because of anticipated difficulties with the rope transmission.[9] Figure 23.—Backmann’s proposed helicoidal elevator for the upper section of the Eiffel Tower. That the Backmann system should have been given serious consideration at all reflects the uncertainty surrounding the entire matter of providing elevator service of such unusual nature. Had the Eiffel Tower been erected only 15 years later, the situation would have been simply one of selection. As it was, Eiffel and the commissioners were governed not by what they wanted but largely by what was available. THE OTIS SYSTEMThe curvature of the Tower’s legs imposed a problem unique in elevator design, and it caused great annoyance to Eiffel, the fair’s Commission, and all others concerned. Since a vertical shaftway anywhere within the open area beneath the first platform was esthetically unthinkable, the elevators could be placed only in the inclined legs. The problem of reaching the first platform was not serious. The legs were wide enough and their curvature so slight in this lower portion as to permit them to contain a straight run of track, and the service could have been designed along the lines of an ordinary inclined railway. It was estimated that the great majority of visitors would go only to this level, attracted by the several international restaurants, bars and other features located there. Two elevators to operate only that far were contracted for with no difficulty—one to be placed in the east leg and one in the west. To transport people to the second platform was an altogether different problem. Since there was to be a single run from the ground, it would have been necessary to form the elevator guides either with a constant curvature, approximating that of the legs, or with a series of straight chords connected by short segmental curves of small radius. Eiffel planned initially to use the first method, but the second was adopted ultimately, probably as being the simpler because only two straight lengths of run were found to be necessary. Bids were invited for two elevators on this basis—one each for the north and south legs. Here the unprecedented character of the matter became evident—there was not a firm in France willing to undertake the work. The American Elevator Company, the European branch of Otis Brothers & Company, did submit a proposal through its Paris office, Otis Ascenseur Cie., but the Commission was compelled to reject it because a clause in the fair’s charter prohibited the use of any foreign material in the construction of the Tower. Furthermore, there was a strong prejudice against foreign contractors, which, because of the general background of disfavor surrounding the project during its early stages, was an element worth serious consideration by the Commission. The bidding time was extended, and many attempts were made to attract a native design but none was forthcoming. Larger Image Figure 24.—General arrangement of Otis elevator system in Eiffel Tower. (From The Engineer (London), July 19, 1889, vol. 68, p. 58.) “Yes,” said Mr. Hall, “this is the first elevator of its kind. Our people for thirty-eight years have been doing this work, and have constructed thousands of elevators vertically, and many on an incline, but never one to strike a radius of 160 feet for a distance of over 50 feet. It has required a great amount of preparatory study and we have worked on it for three years.” “That was before you got the contract?” “Quite so, but we knew that, although the French authorities were very reluctant to give away this piece of work, they would be bound to come to us, and so we were preparing for them.” Such supreme confidence must have rapidly evaporated as events progressed. Despite the invaluable advertising to be derived from an installation of such distinction, the Otises would probably have defaulted had they foreseen the difficulties which preceded completion of the work. The proposed system (fig. 24) was based fundamentally upon Otis’ standard hydraulic elevator, but it was recognizable only in basic operating principle (fig. 25). Tracks of regular rail section replaced the guides because of the incline, and the double-decked cabin (fig. 29) ran on small flanged wheels. This much of the apparatus was really not unlike that of an ordinary inclined railway. Motive power was provided by the customary hydraulic cylinder (fig. 26), set on an angle roughly equal to the incline of the lower section of run. Balancing the cabin’s dead weight was a counterpoise carriage (fig. 27) loaded with pig iron that traveled on a second set of rails beneath the main track. Like the driving system, the counterweight was rope-geared, 3 to 1, so that its travel was about 125 feet to the cabin’s 377 feet. Everything about the system was on a scale far heavier than found in the normal elevator of the type. The cylinder, of 38-inch bore, was 36 feet long. Rather than a simple nest of pulleys, the piston rods pulled a large guided carriage or “chariot” bearing six movable sheaves (fig. 28). Corresponding were five stationary sheaves, the whole reeved to form an immense 12-purchase tackle. The car, attached to the free ends of the cables, was hauled up as the piston drew the two sheave assemblies apart. Figure 25.—Schematic diagram of the rigging of the Otis system. In examining the system, it is difficult to determine what single element in its design might have caused such a problem as to have been beyond the engineering ability of a French firm, and to have caused such concern to a large, well-established American organization of Otis’ wide elevator and inclined railway experience. Indeed, when the French system—which served the first platform from the east and west legs—is examined, it appears curious that a national technology capable of producing a machine at such a level of complexity should have been unable to deal easily with the entire matter. This can be plausibly explained only on the basis of Europe’s previously mentioned lack of experience with rope-geared and other cable-hung elevator systems. The difficulty attending Otis’ work, usually true in the case of all innovations, lay unquestionably in the multitudes of details—many of them, of course, invisible when only the successfully working end product is observed. More than a matter of detail was the Commission’s demand for perfect safety, which precipitated a situation typical of many confronting Otis during the entire work. Otis had wished to coordinate the entire design process through Mr. Hall, with technical matters handled by mail. Nevertheless, at Eiffel’s insistence, and with some inconvenience, in 1888 the company dispatched the project’s engineer, Thomas E. Brown, Jr., to Paris for a direct consultation. Mild conflict over minor details ensued, but a gross difference of opinion arose ultimately between the American and French engineers over the safety of the system. The disagreement threatened to halt the entire project. In common with all elevators in which the car hangs by cables, the prime consideration here was a means of arresting the cabin should the cables fail. As originally presented to Eiffel, the plans indicated an elaborate modification of the standard Otis safety device—itself a direct derivative of E. G. Otis’ original. If any one of the six hoisting cables broke or stretched unduly, or if their tension slackened for any reason, powerful leaf springs were released causing brake shoes to grip the rails. The essential feature of the design was the car’s arrest by friction between its grippers and the rails so that the stopping action was gradual, not sudden as in the elevator safety. During proof trials of the safety, made prior to the fair’s opening by cutting away a set of temporary hoisting cables, the cabin would fall about 10 feet before being halted. Figure 26.—Section through the Otis power cylinder. Figure 27.—Details of the counterweight carriage in the Otis system. Although highly efficient and of unquestionable security, this safety device was considered an insufficient safeguard by Eiffel, who, speaking in the name of the Commission, demanded the application of a device known as the rack and pinion safety that was used to some extent on European cog railways. The commissioners not only considered this system more reliable but felt that one of its features was a necessity: a device that permitted the car to be lowered by hand, even after failure of all the hoisting cables. The serious shortcomings of the rack and pinion were its great noisiness and the limitation it imposed on hoisting speed. Both disadvantages were due to the constant engagement of a pinion on the car with a continuous rack set between the rails. The meeting ended in an impasse, with Brown unwilling to approve the objectionable apparatus and able only to return to New York and lay the matter before his company. While Eiffel’s attitude in the matter may appear highly unreasonable, it must be said that during a subsequent meeting between Brown and Koechlin, the French engineer implied that a mutual antagonism had arisen between the Tower’s creator and the Commission. Thus, since his own judgment must have had little influence with the commissioners at that time, Eiffel was compelled to specify what he well knew were excessive safety provisions. This decision placed Otis Brothers in a decidedly uncomfortable position, at the mercy of the Commission. W. E. Hale, promoter of the water balance elevator—who by then had a strong voice in Otis’ affairs—expressed the seriousness of the matter in a letter to the company’s president, Charles R. Otis, following receipt of Brown’s report on the Paris conference. Referring to the controversial cogwheel, Hale wrote ... if this must be arranged so that the car is effected [sic] in its operation by constant contact with the rack and pinion ... so as to communicate the noise and jar, and unpleasant motion which such an arrangement always produces, I should favor giving up the whole matter rather than allying ourselves with any such abortion.... we would be the laughing stock of the world, for putting up such a contrivance. This difficult situation apparently was the product of a somewhat general contract phrased in terms of service to be provided rather than of specific equipment to be used. This is not unusual, but it did leave open to later dispute such ambiguous clauses as “adequate safety devices are to be provided.” Although faced with the loss not only of all previously expended design work but also of an advertisement of international consequence, the company apparently concurred with Hale and so advised Paris. Unfortunately, there are no Otis records to reveal the subsequent transactions, but we may assume that Otis’ threat of withdrawal prevailed, coupled as it was with Eiffel’s confidence in the American equipment. The system went into operation as originally designed, free of the odious rack and pinion. That, unfortunately, was not the final disagreement. Before the fair’s opening in May 1889, the relationship was strained so drastically that a mutually satisfactory conclusion to the project must indeed have seemed hopeless. The numerous minor structural modifications of the Tower legs found necessary as construction progressed had necessitated certain equivalent alteration to the Otis design insofar as its dependency upon After all else we have borne and suffered and achieved in your behalf, we regard this as a trifle too much; and we do not hesitate to declare, in the strongest terms possible to the English language, that we will not put up with it ... and, if there is to be War, under the existing circumstances, propose that at least part of it shall be fought on American ground. If Mr. Eiffel shall, on the contrary, treat us as we believe we are entitled to be treated, under the circumstances, and his confidence in our integrity to serve him well shall be restored in season to admit of the completion of this work at the time wanted, well and good; but it must be done at once ... otherwise we shall ship no more work from this side, and Mr. Eiffel must charge to himself the consequences of his own acts. This message apparently had the desired effect and the matter was somehow resolved, as the machinery was in full operation when the Exposition opened. The installation must have had immense promotional value for Otis Brothers, particularly in its contrast to the somewhat anomalous French system. This contrast evidently was visible to the technically unsophisticated as well as to visiting engineers. Several newspapers reported that the Otis elevators were one of the best American exhibits at the fair. In spite of their large over-all scale and the complication of the basic pattern imposed by the unique situation, the Otis elevators performed well and justified the original judgment and confidence which had prompted Eiffel to fight for their installation. Aside from the obvious advantage of simplicity when compared to the French machines, their operation was relatively quiet, and fast. The double car, traveling at 400 feet per minute, carried 40 persons, all seated because of the change of inclination. The main valve or distributor that controlled the flow of water to and from the driving cylinder was operated from the car by cables. The hydraulic head necessary to produce pressure within the cylinder was obtained from a large open reservoir on the second platform. After being exhausted from the cylinder, the water was pumped back up by two Girard pumps (fig. 31) in the engine room at the base of the Tower’s south leg. THE SYSTEM OF ROUX, COMBALUZIER AND LEPAPEThere can be little doubt that the French elevators placed in the east and west piers to carry visitors to the first stage of the Tower had the important secondary function of saving face. That an engineer of Eiffel’s mechanical perception would have permitted their use, unless compelled to do so by the Exposition Commission, is unthinkable. Whatever the attitudes of the commissioners may have been, it must be said—recalling the Backmann system—that they did not fear innovation. The machinery installed by the firm of Roux, Combaluzier and Lepape was novel in every respect, but it was a product of misguided ingenuity and set no precedent. The system, never duplicated, was conceived, born, lived a brief and not overly creditable life, and died, entirely within the Tower. Basis of the French system was an endless chain of short, rigid, articulated links (fig. 35), to one point of which the car was attached. As the chain moved, the car was raised or lowered. Recalling the European distrust of suspended elevators, it is interesting to note that the car was pushed up by the links below, not drawn by those above, thus the active links were in compression. To prevent buckling of the column, the chain was enclosed in a conduit (fig. 36). Excessive friction was prevented by a pair of small rollers at each of the knuckle joints between the links. The system was, in fact, a duplicate one, with a chain on either side of the car. At the bottom of the run the chains passed around huge sprocket wheels, 12.80 feet in diameter, with pockets on their peripheries to engage the joints. Smaller wheels at the top guided the chains. If by some motive force the wheel (fig. 33) were turned counterclockwise, the lower half of the chain would be driven upward, carrying the car with it. Slots on the inside faces of the lower guide trunks permitted passage of the connection between the car and chain. Lead weights on certain links of the chains’ upper or return sections counterbalanced most of the car’s dead weight. Figure 28.—Plan and section of the Otis system’s movable pulley assembly, or chariot. Piston rods are at left. Two horizontal cylinders rotated the driving sprockets through a mechanism whose effect was similar to the rope-gearing of the standard hydraulic elevator, but which might be described as chain gearing. The cylinders were of the pushing rather than the pulling type used in the Otis system; that is, the pressure was introduced behind the plungers, driving them out. To the ends of the plungers were fixed smooth-faced sheaves, over which were looped heavy quadruple-link pitch chains, one end of each being solidly attached to the machine base. The free ends ran under the cylinder and made another half-wrap around small sprockets keyed to the main drive shaft. As the plungers were forced outward, the free ends of the chain moved in the opposite direction, at twice the velocity and linear displacement of the plungers. The drive sprockets were thereby revolved, driving up the car. Descent was made simply by permitting the cylinders to exhaust, the car dropping of its own weight. The over-all gear or ratio of the system was the multiplication due to the double purchase of the plunger sheaves times the ratio of the chain and drive sprocket diameters: 2(12.80/1.97) or about 13:1. To drive the car 218 feet to the first platform of the Tower the plungers traveled only about 16.5 feet. To penetrate the inventive rationale behind this strange machine is not difficult. Aware of the fundamental dictum of absolute safety before all else, the Roux engineers turned logically to the safest known elevator type—the direct plunger. This type of elevator, being well suited to low rises, formed the main body of European practice at the time, and in this fact lay the further attraction of a system firmly based on tradition. Since the piers between the ground and first platform could accommodate a straight, although inclined run, the solution might obviously have been to use an inclined, direct plunger. The only difficulty would have been that of drilling a 220-foot, inclined well for the cylinder. While a difficult problem, it would not have been insurmountable. What then was the reason for using a design vastly more complex? The only reasonable answer that presents itself is that the designers, working Figure 29.—Section through cabin of the Otis elevator. Note the pivoted floor-sections. Here then was a design exhibiting strange contrast. It was on the one hand completely novel, devised expressly for this trying service; yet on the other hand it was derived from and fundamentally based on a thoroughly traditional system. If nothing else, it was safe beyond question. In Eiffel’s own words, the Roux lifts “not only were safe, but appeared safe; a most desirable feature in lifts traveling to such heights and carrying the general public.”[12] The system’s shortcomings could hardly be more evident. Friction resulting from the more than 320 joints in the flexible pistons, each carrying two rollers, plus that from the pitch chains must have been immense. The noise created by such multiplicity of parts can only be imagined. Capacity was equivalent to that of the Otis system. About 100 people could be carried in the double-deck cabin, some standing. The speed, however, was only 200 feet per minute, understandably low. If it had been the initial intention of the designers to operate their cars to the second platform, they must shortly have become aware of the impracticability of this plan, caused by an inherent characteristic of the apparatus. As long as the compressive force acted along the longitudinal axis of the links, there was no lateral resultant and the only load on the small rollers was that due to the dead weight of the link itself. However, if a curve had been introduced in the guide channels to increase the incline of the upper run, as done by Otis, the force on those links traversing the bend would have been eccentric—assuming the car to be in the upper section, above the bend. The difference between the two sections (based upon the Otis system) was 78°9' minus 54°35', or 23°34', the tangent of which equals 0.436. Forty-three percent of the unbalanced weight of the car and load would then have borne upon the, say, 12 sets of rollers on the curve. The immense frictional load thus added to the entire system would certainly have made it dismally inefficient, if not actually unworkable. In spite of Eiffel’s public remarks regarding the safety of the Roux machinery, in private he did not trouble to conceal his doubts. Otis’ representative, Hall, discussing this toward the end of Brown’s previously mentioned report, probably presented a fairly accurate picture of the situation. His comments were based on conversations with Eiffel and Koechlin: Mr. Gibson, Mr. Hanning [who were other Otis employees] and myself came to the unanimous conclusion that Mr. Eiffel had been forced to order those other machines, from outside parties, against his own judgment: and that he was very much in doubt as to their being a practical success—and was, therefore, all the more anxious to put in our machines Figure 30.—Upperworks and passenger platforms of the Otis system at second level. The Roux and the Otis systems both drew their water supply from the same tanks; also, each system used similar distributing valves (fig. 32) operated from the cars. Although no reports have been found of actual controlled tests comparing the efficiencies of the Otis and Roux systems, a general quantitative comparison may be made from the balance figures given for each (p. 40), where it is seen that 2,665 pounds of excess tractive effort were allowed to overcome the friction of the Otis machinery against 13,856 pounds for the Roux. THE EDOUX SYSTEMThe section of the Tower presenting the least difficulty to elevator installation was that above the juncture of the four legs—from the second platform to the third, or observation, enclosure. There was no question that French equipment could perform this service. The run being perfectly straight and vertical, the only unusual demand upon contemporary elevator technology was the length of rise—525 feet. The system ultimately selected (fig. 37) appealed to the Commission largely because of a similar one that had been installed in one tower of the famous Trocadero[13] and which had been operating successfully for 10 years. It was the direct plunger system of Leon Edoux, and was, for the time, far more rationally contrived than Backmann’s helicoidal system. Edoux, an old schoolmate of Eiffel’s, had built thousands of elevators in France and was possibly the country’s most successful inventor and manufacturer in the field. It is likely that he did not attempt to obtain the contract for the elevator equipment in the Tower legs, as his experience was based almost entirely on plunger systems, a type, as we have seen, not readily adaptable to that situation. What is puzzling was the failure of the Commission’s members to recognize sooner Edoux’s obvious ability to provide equipment for the upper run. It may have been due to their inexplicable confidence in Backmann. Figure 31.—The French Girard pumps that supplied the Otis and Roux systems. The direct plunger elevator was the only type in which European practice was in advance of American practice at this time. Not until the beginning of the 20th century, when hydraulic systems were forced into competition with electrical systems, was the direct plunger elevator improved in America to the extent of being practically capable of high rises and speeds. Another reason for its early disfavor in the United States was the necessity for drilling an expensive plunger well equal in length to the rise.[14] As mentioned, the most serious problem confronting Edoux was the extremely high rise of 525 feet. The Trocadero elevator, then the highest plunger machine in the world, traveled only about 230 feet. A secondary difficulty was the esthetic undesirability of permitting a plunger cylinder to project downward a distance equal to such a rise, which would have carried it directly into the center of the open area beneath the first platform (fig. 6). Both problems were met by an ingenious modification of the basic system. The run was divided into two equal sections, each of 262 feet, and two cars were used. One operated from the bottom of the run at the second platform level to an intermediate platform half-way up, while the other operated from this point to the observation platform near the top of the Tower. The two sections were of course parallel, but offset. A central guide, on the Tower’s center-line, running the entire 525 feet served both cars, with shorter guides on either side—one for the upper and one for the lower run. Thus, each car traveled only half the total distance. The two cars were connected, as in the Backmann system, by steel cables running over sheaves at the Figure 32.—The Otis distributor, with valves shown in motionless, neutral position. Figure 33.—General arrangement of the Roux Combaluzier and Lepape elevator. Figure 34.—Roux, Combaluzier and Lepape machinery and cabin at the Tower’s base. In operation, water was admitted to the two cylinders from a tank on the third platform. The resultant hydraulic head was sufficient to force out the rams and raise the upper car. As the rams and car rose, the rising water level in the cylinders caused a progressive reduction of the available head. This negative effect was further heightened by the fact that, as the rams moved upward, less and less of their length was buoyed by the water within the cylinders, increasing their effective weight. These two factors were, however, exactly compensated for by the lengthening of the cables on the other side of the pulleys as the lower car descended. Perfect balance of the system’s dead load for any position of the cabins was, therefore, a quality inherent in its design. However, there were two extreme conditions of live loading which required consideration: the lower car full and the upper empty, or vice versa. To permit the upper car to descend under the first condition, the plungers were made sufficiently heavy, by the addition of cast iron at their lower ends, to overbalance the weight of a capacity load in the lower car. The second condition demanded simply that the system be powerful enough to lift the unbalanced weight of the plungers plus the weight of passengers in the upper car. As in the other systems, safety was a matter of prime importance. In this case, the element of risk lay in the possibility of the suspended car falling. The upper car, resting on the rams, was virtually free of such danger. Here again the influence of Backmann was felt—a brake of his design was applied (fig. 38). It was, true to form, a throwback, similar safety devices having proven unsuccessful much earlier. Attached to the lower car were two helically threaded vertical
The device was considered ineffectual by Edoux and Eiffel, who were aware that the ultimate safety of the system resulted from the use of supporting cables far heavier than necessary. There were four such cables, with a total sectional area of 15.5 square inches. The total maximum load to which the cables might be subjected was about 47,000 pounds, producing a stress of about 3,000 pounds per square inch compared to a breaking stress of 140,000 pounds per square inch—a safety factor of 46![16]
A curiosity in connection with the Edoux system was the use of Worthington (American) pumps (fig. 40) to carry the water exhausted from the cylinders back to the supply tanks. No record has been found that might explain why this particular exception was made to the “foreign materials” stipulation. This exception is even more strange in view of Otis’ futile request for the same pumps and the fact that any number of native machines must have been available. It is possible that Edoux’s personal influence was sufficient to overcome the authority of the regulation. Figure 39.—Passengers changing cars on Edoux elevator at intermediate platform. Figure 40.—Worthington tandem compound steam pumps, at base of the Tower’s south pier, Figure 41.—Recent view of lower car of the Edoux system, |
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