Posted by smartshyam on Nov. 27, 2013, 9:33 p.m.
The Eiffel Tower (French: La Tour Eiffel, [tu? ?f?l]) is an iron lattice tower located on the Champ de Mars in Paris. It was named after the engineer Gustave Eiffel, whose company designed and built the tower. Erected in 1889 as the entrance arch to the 1889 World's Fair, it has become both a global cultural icon of France and one of the most recognizable structures in the world. The tower is the tallest structure in Paris[10] and the most-visited paid monument in the world; 7.1 million people ascended it in 2011. The tower received its 250 millionth visitor in 2010.
The tower stands 324 metres (1,063 ft) tall, about the same height as an 81-storey building. During its construction, the Eiffel Tower surpassed the Washington Monument to assume the title of the tallest man-made structure in the world, a title it held for 41 years, until the Chrysler Building in New York City was built in 1930. Because of the addition of the antenna atop the Eiffel Tower in 1957, it is now taller than the Chrysler Building by 5.2 metres (17 ft). Not including broadcast antennas, it is the second-tallest structure in France, after the Millau Viaduct.
The tower has three levels for visitors. The third level observatory's upper platform is at 279.11 m (915.7 ft) the highest accessible to the public in the European Union. Tickets can be purchased to ascend, by stairs or lift (elevator), to the first and second levels. The walk from ground level to the first level is over 300 steps, as is the walk from the first to the second level. Although there are stairs to the third and highest level, these are usually closed to the public and it is usually accessible only by lift. The first and second levels have restaurants.
Work on the foundations started in January 1887. Those for the east and south legs were straightforward, each leg resting on four 2 m (6.6 ft) concrete slabs, one for each of the principal girders of each leg but the other two, being closer to the river Seine, were more complicated: each slab needed two piles installed by using compressed-air caissons 15 m (49 ft) long and 6 m (20 ft) in diameter driven to a depth of 22 m (72 ft)[20] to support the concrete slabs, which were 6 m (20 ft) thick. Each of these slabs supported a block built of limestone each with an inclined top to bear a supporting shoe for the ironwork. Each shoe was anchored into the stonework by a pair of bolts 10 cm (4 in) in diameter and 7.5 m (25 ft) long. The foundations were complete by 30 June and the erection of the ironwork began. The very visible work on-site was complemented by the enormous amount of exacting preparatory work that was entailed: the drawing office produced 1,700 general drawings and 3,629 detailed drawings of the 18,038 different parts needed.[21] The task of drawing the components was complicated by the complex angles involved in the design and the degree of precision required: the position of rivet holes was specified to within 0.1 mm (0.04 in) and angles worked out to one second of arc. The finished components, some already riveted together into sub-assemblies, arrived on horse-drawn carts from the factory in the nearby Parisian suburb of Levallois-Perret and were first bolted together, the bolts being replaced by rivets as construction progressed. No drilling or shaping was done on site: if any part did not fit it was sent back to the factory for alteration. In all there were 18,038 pieces joined by two and a half million rivets.[22]
At first the legs were constructed as cantilevers but about halfway to the first level construction was paused in order to construct a substantial timber scaffold. This caused a renewal of the concerns about the structural soundness of the project, and sensational headlines such as "Eiffel Suicide!" and "Gustave Eiffel has gone mad: he has been confined in an Asylum" appeared in the popular press.[23] At this stage a small "creeper" crane was installed in each leg, designed to move up the tower as construction progressed and making use of the guides for the lifts which were to be fitted in each leg. The critical stage of joining the four legs at the first level was complete by March 1888. Although the metalwork had been prepared with the utmost precision, provision had been made to carry out small adjustments in order to precisely align the legs: hydraulic jacks were fitted to the shoes at the base of each leg, each capable of exerting a force of 800 tonnes, and in addition the legs had been intentionally constructed at a slightly steeper angle than necessary, being supported by sandboxes on the scaffold.
Although construction involved 300 on-site employees, only one person died thanks to Eiffel's stringent safety precautions and use of movable stagings, guard-rails, and screens.
Inauguration and the 1889 Exposition
The main structural work was completed at the end of March 1889 and on the 31st Eiffel celebrated this by leading a group of government officials, accompanied by representatives of the press, to the top of the tower. Since the lifts were not yet in operation, the ascent was made by foot, and took over an hour, Eiffel frequently stopping to make explanations of various features. Most of the party chose to stop at the lower levels, but a few, including Nouguier, Compagnon, the President of the City Council and reporters from Le Figaro and Le Monde Illustré completed the climb. At 2.35 Eiffel hoisted a large tricolore, to the accompaniment of a 25-gun salute fired from the lower level.[24] There was still work to be done, particularly on the lifts and the fitting out of the facilities for visitors, and the tower was not opened to the public until nine days after the opening of the Exposition on 6 May, and even then the lifts had not been completed.
The tower was an immediate success with the public, and lengthy queues formed to make the ascent. Tickets cost 2 francs for the first level, 3 for the second, and 5 for the top, with half-price admission on Sundays, and by the end of the exhibition there had been nearly two million visitors.[25]
Eiffel had a permit for the tower to stand for 20 years; it was to be dismantled in 1909, when its ownership would revert to the City of Paris. The City had planned to tear it down (part of the original contest rules for designing a tower was that it could be easily demolished) but as the tower proved valuable for communication purposes, it was allowed to remain after the expiration of the permit. In the opening weeks of World War I, powerful radio transmitters were fitted to the tower in order to jam German communications. This seriously hindered their advance on Paris, and contributed to the Allied victory at the First Battle of the Marne.[26]
Material
The puddled iron[39] (wrought iron) structure of the Eiffel Tower weighs 7,300 tonnes, while the entire structure, including non-metal components, is approximately 10,000 tonnes. As a demonstration of the economy of design, if the 7,300 tonnes of the metal structure were melted down it would fill the 125-metre-square base to a depth of only 6 cm (2.36 in), assuming the density of the metal to be 7.8 tonnes per cubic metre. Depending on the ambient temperature, the top of the tower may shift away from the sun by up to 18 cm (7.1 in) because of thermal expansion of the metal on the side facing the sun.