Elevator Systems of the Eiffel Tower Part 1

Elevator Systems of the Eiffel Tower.

1889.

by Robert M. Vogel.

_This article traces the evolution of the powered pa.s.senger elevator from its initial development in the mid-19th century to the installation of the three separate elevator systems in the Eiffel Tower in 1889. The design of the Tower's elevators involved problems of capacity, length of rise, and safety far greater than any previously encountered in the field; and the equipment that resulted was the first capable of meeting the conditions of vertical transportation found in the just emerging skysc.r.a.per._

THE AUTHOR: _Robert M. Vogel is a.s.sociate curator of mechanical and civil engineering, United States National Museum, Smithsonian Inst.i.tution._

The 1,000-foot tower that formed the focal point and central feature of the Universal Exposition of 1889 at Paris has become one of the best known of man's works. It was among the most outstanding technological achievements of an age which was itself remarkable for such achievements.

Second to the interest shown in the tower's structural aspects was the interest in its mechanical organs. Of these, the most exceptional were the three separate elevator systems by which the upper levels were made accessible to the Exposition visitors. The design of these systems involved problems far greater than had been encountered in previous elevator work anywhere in the world. The basis of these difficulties was the amplification of the two conditions that were the normal determinants in elevator design--pa.s.senger capacity and height of rise. In addition, there was the problem, totally new, of fitting elevator shafts to the curvature of the Tower's legs. The study of the various solutions to these problems presents a concise view of the capabilities of the elevator art just prior to the beginning of the most recent phase of its development, marked by the entry of electricity into the field.

The great confidence of the Tower's builder in his own engineering ability can be fully appreciated, however, only when notice is taken of one exceptional way in which the project differed from works of earlier periods as well as from contemporary ones. In almost every case, these other works had evolved, in a natural and progressive way, from a fundamental concept firmly based upon precedent. This was true of such notable structures of the time as the Brooklyn Bridge and, to a lesser extent, the Forth Bridge. For the design of his tower, there was virtually no experience in structural history from which Eiffel could draw other than a series of high piers that his own firm had designed earlier for railway bridges. It was these designs that led Eiffel to consider the practicality of iron structures of extreme height.

[Ill.u.s.tration: Figure 1.--The Eiffel Tower at the time of the Universal Exposition of 1889 at Paris. (From _La Nature_, June 29, 1889, vol. 17, p.

73.)]

[Ill.u.s.tration: Figure 2.--Gustave Eiffel (1832-1923). (From Gustave Eiffel, _La Tour de Trois Cents Metres_, Paris, 1900, frontispiece.)]

There was, it is true, some inspiration to be found in the paper projects of several earlier designers--themselves inspired by that compulsion which throughout history seems to have driven men to attempt the erection of magnificently high structures.

One such inspiration was a proposal made in 1832 by the celebrated but eccentric Welsh engineer Richard Trevithick to erect a 1,000-foot, conical, cast-iron tower (fig. 3) to celebrate the pa.s.sing of the Reform Bill. Of particular interest in light of the present discussion was Trevithick's plan to raise visitors to the summit on a piston, driven upward within the structure's hollow central tube by compressed air. It probably is fortunate for Trevithick's reputation that his plan died shortly after this and the project was forgotten.

One project of genuine promise was a tower proposed by the eminent American engineering firm of Clarke, Reeves & Company to be erected at the Centennial Exhibition at Philadelphia in 1876. At the time, this firm was perhaps the leading designer and erector of iron structures in the United States, having executed such works as the Girard Avenue Bridge over the Schuylkill at Fairmount Park, and most of New York's early elevated railway system. The company's proposal (fig. 4) for a 1,000-foot shaft of wrought-iron columns braced by a continuous web of diagonals was based upon sound theoretical knowledge and practical experience. Nevertheless, the natural hesitation that the fair's sponsors apparently felt in the face of so heroic a scheme could not be overcome, and this project also remained a vision.

Preparatory Work for the Tower

In the year 1885, the Eiffel firm, which also had an extensive background of experience in structural engineering, undertook a series of investigations of tall metallic piers based upon its recent experiences with several lofty railway viaducts and bridges. The most spectacular of these was the famous Garabit Viaduct (1880-1884), which carries a railroad some 400 feet above the valley of the Truyere in southern France. While the 200-foot height of the viaduct's two greatest piers was not startling even at that period, the studies proved that piers of far greater height were entirely feasible in iron construction. This led to the design of a 395-foot pier, which, although never incorporated into a bridge, may be said to have been the direct basis for the Eiffel Tower.

Preliminary studies for a 300-meter tower were made with the 1889 fair immediately in mind. With an a.s.surance born of positive knowledge, Eiffel in June of 1886 approached the Exposition commissioners with the project.

There can be no doubt that only the singular respect with which Eiffel was regarded not only by his profession but by the entire nation motivated the Commission to approve a plan which, in the hands of a figure of less stature, would have been considered grossly impractical.

Between this time and commencement of the Tower's construction at the end of January 1887, there arose one of the most persistently annoying of the numerous difficulties, both structural and social, which confronted Eiffel as the project advanced. In the wake of the initial enthusiasm--on the part of the fair's Commission inspired by the desire to create a monument to French technological achievement, and on the part of the majority of Frenchmen by the stirring of their imagination at the magnitude of the structure--there grew a rising movement of disfavor. The nucleus was, not surprisingly, formed mainly of the intelligentsia, but objections were made by prominent Frenchmen in all walks of life. The most interesting point to be noted in a retrospection of this often violent opposition was that, although the Tower's every aspect was attacked, there was remarkably little criticism of its structural feasibility, either by the engineering profession or, as seems traditionally to be the case with bold and unprecedented undertakings, by large numbers of the technically uninformed laity. True, there was an undercurrent of what might be characterized as unease by many property owners in the structure's shadow, but the most obstinate element of resistance was that which deplored the Tower as a mechanistic intrusion upon the architectural and natural beauties of Paris. This resistance voiced its fury in a flood of special newspaper editions, pet.i.tions, and manifestos signed by such lights of the fine and literary arts as De Maupa.s.sant, Gounod, Dumas _fils_, and others. The eloquence of one article, which appeared in several Paris papers in February 1887, was typical:

We protest in the name of French taste and the national art culture against the erection of a staggering Tower, like a gigantic kitchen chimney dominating Paris, eclipsing by its barbarous ma.s.s Notre Dame, the Sainte-Chapelle, the tower of St. Jacques, the Dome des Invalides, the Arc de Triomphe, humiliating these monuments by an act of madness.[1]

Further, a prediction was made that the entire city would become dishonored by the odious shadow of the odious column of bolted sheet iron.

It is impossible to determine what influence these outcries might have had on the project had they been organized sooner. But inasmuch as the Commission had, in November 1886, provided 1,500,000 francs for its commencement, the work had been fairly launched by the time the protestations became loud enough to threaten and they were ineffectual.

Upon completion, many of the most vigorous protestants became as vigorous in their praise of the Tower, but a hard core of critics continued for several years to circulate pet.i.tions advocating its demolition by the government. One of these critics, it was said--probably apocryphally--took an office on the first platform, that being the only place in Paris from which the Tower could not be seen.

[Ill.u.s.tration: Figure 3.--Trevithick's proposed cast-iron tower (1832) would have been 1,000 feet high, 100 feet in diameter at the base, 12 feet at the top, and surmounted by a colossal statue. (From F. Dye, _Popular Engineering_, London, 1895, p. 205.)]

The Tower's Structural Rationale

During the previously mentioned studies of high piers undertaken by the Eiffel firm, it was established that as the base width of these piers increased in proportion to their height, the diagonal bracing connecting the vertical members, necessary for rigidity, became so long as to be subject to high flexural stresses from wind and columnar loading. To resist these stresses, the bracing required extremely large sections which greatly increased the surface of the structure exposed to the wind, and was, moreover, decidedly uneconomical. To overcome this difficulty, the principle which became the basic design concept of the Tower was developed.

The material which would otherwise have been used for the continuous lattice of diagonal bracing was concentrated in the four corner columns of the Tower, and these verticals were connected only at two widely separated points by the deep bands of trussing which formed the first and second platforms. A slight curvature inward was given to the main piers to further widen the base and increase the stability of the structure. At a point slightly above the second platform, the four members converged to the extent that conventional bracing became more economical, and they were joined.

[Ill.u.s.tration: Figure 4.--The proposed 1,000-foot iron tower designed by Clarke, Reeves & Co. for the Centennial Exhibition of 1876 at Philadelphia. (From _Scientific American_, Jan. 24, 1874, vol. 30, p.

47.)]

That this theory was successful not only practically, but visually, is evident from the resulting work. The curve of the legs and the openings beneath the two lower platforms are primarily responsible for the Tower's graceful beauty as well as for its structural soundness.

The design of the Tower was not actually the work of Eiffel himself but of two of his chief engineers, Emile Nouguier (1840-?) and Maurice Koechlin (1856-1946)--the men who had conducted the high pier studies--and the architect Stephen Sauvestre (1847-?).

In the planning of the foundations, extreme care was used to ensure adequate footing, but in spite of the Tower's light weight in proportion to its bulk, and the low earth pressure it exerted, uneven pier settlement with resultant leaning of the Tower was considered a dangerous possibility.[2] To compensate for this eventuality, a device was used whose ingenious directness justifies a brief description. In the base of each of the 16 columns forming the four main legs was incorporated an opening into which an 800-ton hydraulic press could be placed, capable of raising the member slightly. A thin steel s.h.i.+m could then be inserted to make the necessary correction (fig. 5). The system was used only during construction to overcome minor erection discrepancies.

In order to appreciate fully the problem which confronted the Tower's designers and sponsors when they turned to the problem of making its observation areas accessible to the fair's visitors, it is first necessary to investigate briefly the contemporary state of elevator art.

Elevator Development before the Tower

While power-driven hoists and elevators in many forms had been used since the early years of the 19th century, the ever-present possibility of breakage of the hoisting rope restricted their use almost entirely to the handling of goods in mills and warehouses.[3] Not until the invention of a device which would positively prevent this was there much basis for work on other elements of the system. The first workable mechanism to prevent the car from dropping to the bottom of the hoistway in event of rope failure was the product of Elisha G. Otis (1811-1861), a mechanic of Yonkers, New York. The invention was made more or less as a matter of course along with the other machinery for a new mattress factory of which Otis was master mechanic.

[Ill.u.s.tration: Figure 5.--Correcting erection discrepancies by raising pier member--with hydraulic press and hand pump--and inserting s.h.i.+ms.

(From _La Nature_, Feb. 18, 1888, vol. 16, p. 184.)]

[Ill.u.s.tration: Figure 6.--The promenade beneath the Eiffel Tower, 1889.

(From _La Nature_, Nov. 30, 1889, vol. 17, p. 425.)]

[Ill.u.s.tration: Figure 7.--Teagle elevator in an English mill about 1845.

Power was taken from the line shafting. (From _Pictorial Gallery of Arts_, Volume of Useful Arts, London, n.d. [ca. 1845].)]

The importance of this invention soon became evident to Otis, and he introduced his device to the public three years later during the second season of the New York Crystal Palace Exhibition, in 1854. Here he would demonstrate dramatically the perfect safety of his elevator by cutting the hoisting rope of a suspended platform on which he himself stood, uttering the immortal words which have come to be inseparably a.s.sociated with the history of the elevator--"All safe, gentlemen!"[4]

The invention achieved popularity slowly, but did find increasing favor in manufactories throughout the eastern United States. The significance of Otis' early work in this field lay strictly in the safety features of his elevators rather than in the hoisting equipment. His earliest systems were operated by machinery similar to that of the teagle elevator in which the hoisting drum was driven from the mill shafting by simple fast and loose pulleys with crossed and straight belts to raise, lower, and stop. This scheme, already common at the time, was itself a direct improvement on the ancient hand-powered drum hoist.