Eiffel Tower
Wind and weather considerations

When it was built, many were shocked by the tower's daring form. Eiffel was accused of trying to create something artistic with no regard to the principles of engineering. However, Eiffel and his team – 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 sure it could withstand them. In an interview with the newspaper Le Temps published on 14 February 1887, Eiffel said:

Is it not true that the very conditions which give strength also conform to the hidden rules of harmony?... Now to what phenomenon did I have to 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.

He used graphical methods to determine the strength of the tower and empirical evidence to account for the effects of wind, rather than a mathematical formula. Close examination of the tower reveals a basically exponential shape. All parts of the tower were overdesigned to ensure maximum resistance to wind forces. The top half was even assumed to have no gaps in the latticework. In the years since it was completed, engineers have put forward various mathematical hypotheses in an attempt to explain the success of the design. The most recent, devised in 2004 after letters sent by Eiffel to the French Society of Civil Engineers in 1885 were translated into English, is described as a non-linear integral equation based on counteracting the wind pressure on any point of the tower with the tension between the construction elements at that point.

The Eiffel Tower sways by up to 9 cm (3.5 in) in the wind.
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