Eiffel Tower

Eiffel Tower

The Eiffel Tower was built for the International Exhibition of Paris of 1889 commemorating the centenary of the French Revolution. The Prince of Wales, later King Edward VII of England, opened the tower. Of the 700 proposals submitted in a design competition, Gustave Eiffel's was unanimously chosen. However it was not accepted by all at first, and a petition of 300 names - including those of Maupassant, Emile Zola, Charles Garnier (architect of the Opéra Garnier), and Dumas the Younger - protested its construction. At 300 meters (320.75 m including antenna), and 7,000 tons, it was the world's tallest building until 1930. Other statistics include:

1. 2.5 million rivets
2. 300 steel workers, and 2 years (1887-1889) to construct it.
3. Sway of at most 12 cm in high winds.
4. Height varies up to 15 cm depending on temperature.
5. 15,000 iron pieces (excluding rivets). 40 tons of paint. 1652 steps to the top.

In 1889, Gustave Eiffel began to fit the peak of the tower as an observation station to measure the speed of wind. He also encouraged several scientific experiments including Foucault's giant pendulum, a mercury barometer and the first experiment of radio transmission. In 1898, Eugene Ducretet at the Pantheon, received signals from the tower.

 After Gustave Eiffel experiments in the field of meterology, he begun to look at the effects of wind and air resistance, the science that would later be termed aerodynamics, which has become a large part of both military and commercial aviation as well as rocket technology. Gustave Eiffel imagined an automatic device sliding along a cable that was stretched between the ground and the second floor of the Eiffel Tower. 

  

Material

 The 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.

Interior

Wind considerations

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. In an interview reported in the newspaper Le Temps, Eiffel said:

Now to what phenomenon did I give primary concern in designing the Tower? It was wind resistance. Well then! I hold that the curvature of the monument's four outer edges, which is as mathematical calculation dictated it should be  will give a great impression of strength and beauty, for it will reveal to the eyes of the observer the boldness of the design as a whole.

 

 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.

Maintenance

Maintenance of the tower includes applying 50 to 60 tonnes of paint every seven years to protect it from rust. The height of the Eiffel Tower varies by 15 cm due to temperature.

Economics

The American TV show Pricing the Priceless speculates that in 2011 the tower would cost about $480,000,000 to build, that the land under the tower is worth $350,000,000, and that the scrap value of the tower is worth $3,500,000. The TV show estimates the tower makes a profit of about $29,000,000 per year, though it is unlikely that the Eiffel Tower is managed so as to maximize profit.

It costs $5,300,000 to repaint the tower, which is done once every seven years. The electric bill is $400,000 per year for 7.5 million kilowatt-hours.

The Tokey Tower in Japan is a very similar structure of very similar size. It was finished in 1958 at a final cost of ¥2.8 billion ($8.4 million in 1958).

Construction

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) 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: the 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  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 of wrought iron using two and a half million rivets.

At first the legs were constructed as cantilivers 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 senstional headlines such as "Eiffel Suicide!" and "Gustave Eiffel has gone mad: he has been confined in an Asylum" appeared in the popular press. 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 elevators 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 precisly align the legs: hydraulic jackwere 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 sand boxes on the scaffold.

No more than three hundred workers were employed on site, and because Eiffel took safety precautions, including the use of movable stagings, guard-rails and screens, only one man died during construction.