| Sapevatelo [messaggio #156701] |
sab, 07 gennaio 2012 15:42 |
 Fuori-Come-Un-Balcone
Messaggi: 5327
Registrato: marzo 2011 |
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Material
The pig 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.
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.[23]
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.[24][25] As a demonstration of the tower's effectiveness in wind
resistance, it sways only 6–7 cm (2–3 in) in the wind.[24][25][26]
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.
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