Eiffel Tower

The Eiffel Tower (French: La Tour Eiffel, [tu? ?f?l], nickname La dame de fer, the iron lady) is a puddle iron lattice tower located on the Champ de Mars in Paris. Built in 1889, it has become both a global icon of France and one of the most recognizable structures in the world. The tower is the tallest building in Paris[10] and the most-visited paid monument in the world; millions of people ascend it every year. Named after its designer, engineer Gustave Eiffel, the tower was built as the entrance arch to the 1889 World's Fair. 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. However, due to the addition, in 1957, of the antenna atop the Eiffel Tower, it is now taller than the Chrysler Building. Not including broadcast antennas, it is the second-tallest structure in France, after the Millau Viaduct. The tower has three levels for visitors. Tickets can be purchased to ascend, by stairs or lift, 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. The third and highest level is accessible only by elevator. Both the first and second levels feature restaurants. The tower has become the most prominent symbol of both Paris and France, often in the establishing shot of films set in the city.

The structure was built between 1887 and 1889 as the entrance arch for the Exposition Universelle, a World's Fair marking the centennial celebration of the French Revolution. Three hundred workers joined together 18,038 pieces of puddled iron (a very pure form of structural iron), using two and a half million rivets, in a structural design by Maurice Koechlin. Eiffel was assisted in the design by engineers ?mile Nouguier and Maurice Koechlin and architect Stephen Sauvestre. The risk of accident was great as, unlike modern skyscrapers, the tower is an open frame without any intermediate floors except the two platforms. However, because Eiffel took safety precautions, including the use of movable stagings, guard-rails and screens, only one man died. The tower was inaugurated on 31 March 1889, and opened on 6 May. The tower was much criticised by the public when it was built, with many calling it an eyesore. Newspapers of the day were filled with angry letters from the arts community of Paris. One is quoted extensively in William Watson's US Government Printing Office publication of 1892 Paris Universal Exposition: Civil Engineering, Public Works, and Architecture: "And during twenty years we shall see, stretching over the entire city, still thrilling with the genius of so many centuries, we shall see stretching out like a black blot the odious shadow of the odious column built up of riveted iron plates." Signers of this letter included Jean-Louis-Ernest Meissonier, Charles Gounod, Charles Garnier, Jean-L?on G?r?me, William-Adolphe Bouguereau, and Alexandre Dumas.

Novelist Guy de Maupassantt?who claimed to hate the tower?supposedly ate lunch in the Tower's restaurant every day. When asked why, he answered that it was the one place in Paris where one could not see the structure. Today, the Tower is widely considered to be a striking piece of structural art. One of the great Hollywood movie clich?s is that the view from a Parisian window always includes the tower. Since zoning restrictions limit the height of most buildings in Paris to 7 stories, only a few of the taller buildings have a clear view of the tower. 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 expiry of the permit. The military used it to dispatch Parisian taxis to the front line during the First Battle of the Marne.

The pig iron structure of the Eiffel Tower weighs 7,300 tons while the entire structure, including non-metal components, is approximately 10,000?tons. As a demonstration of the economy of design, if the 7,300 tons of the metal structure were melted down it would fill the 125 meter square base to a depth of only 6?cm (2.36?in), assuming the density of the metal to be 7.8 tons per cubic meter. Depending on the ambient temperature, the top of the tower may shift away from the sun by up to 18?cm (7.1?in) due to thermal expansion of the metal on the side facing the sun.

At the time the tower was built many people were shocked by its daring shape. Eiffel was criticised for the design and accused of trying to create something artistic, or inartistic according to the viewer, without regard to engineering. Eiffel and his engineers, however, as experienced bridge builders, understood the importance of wind forces and knew that if they were going to build the tallest structure in the world they had to be certain it would withstand the wind.

Researchers have found that Eiffel used empirical and graphical methods accounting for the effects of wind rather than a specific mathematical formula. Careful examination of the tower shows a basically exponential shape; actually two different exponentials, the lower section overdesigned to ensure resistance to wind forces. Several mathematical explanations have been proposed over the years for the success of the design; the most recent is described as a nonlinear integral equation based on counterbalancing the wind pressure on any point on the tower with the tension between the construction elements at that point. As a demonstration of the tower's effectiveness in wind resistance, it sways only 6?7-cm (2?3-in) in the wind.