The 300m Eiffel Tower: the role of a structural principle

The Eiffel Tower has an iconic curved silhouette which was declared by the Tower’s designer, Gustave Eiffel, to have been determined by the pattern of wind loads acting on the Tower, using a structural principle. Adherence to this principle removed the need for cross-bracing to achieve stability, increasing the structure’s efficiency. When proposed, nothing equalling the Tower’s 300m height had ever been built and there was concern over whether wind loads at this height could be resisted, as well as the visual impact of the Tower. The principle was used to address both concerns, portraying the unusual profile as a technical necessity, rather than an aesthetic choice. However, cross-bracing has been used in the Tower’s top two-thirds, so the role of the principle in the Tower’s design isn’t completely clear. The analysis presented here demonstrates a lack of adherence to the principle in the initial proposals, a good adherence later on, but the final design shows a fundamental deviation from its use. Eiffel’s proclaimed use of the structural principle for reasons of structural efficiency can therefore be seen as a justification of the feasibility and aesthetics of the proposal, masking the uncertainties inherent in designing the tallest Tower at that time.