The Eiffel Tower, daughter of tall metal viaducts
Friday 12 July 2019
Modified the 18/07/19
When the two main engineers of the Eiffel company, Maurice Koechlin and Émile Nouguier, made their first sketch of the 300-meter tall tower, they were in the process of completing the Garabit Viaduct. Work on this beautiful arched metal viaduct had been started a few years earlier. It was one of the largest viaducts ever built in France in its day. The Garabit Viaduct is the twin brother of the Maria Pia Bridge, which Eiffel delivered in 1876 in Porto in Portugal. The Maria Pia Bridge revolutionized the art of bridges by offering a large 160-meter arch supported by pylons in the shape of oblong pyramids to carry the deck, which is the long girder that supports the railroad line.
A tried and true technology for 20 years
Prior to this, Gustave Eiffel had already built many different kinds of metal bridges. They always had large iron lattice beams, often supported by stone piers or relatively high pylons. Starting from the 1870s these pylons were always made of iron, but in 1867, Eiffel used cast iron tubes for the Sioule and Neuvial Viaducts. The four arrises of each pier gracefully curve at the base, evoking a shape that was to foreshadow that of the Eiffel Tower, 20 years in advance..
All of these viaducts were built using technology that had been tried and true since the 1850s: flat iron, corner iron, and plates were assembled with heated rivets in holes pierced in the components beforehand. A large structure such as Garabit Viaduct has no less than 500,000 rivets (the Eiffel Tower has 2.5 million). Most of the rivets were already installed at the factory, in Levallois-Perret, to prefabricate large components which were then sent to the final assembly site. This is exactly the same technology that was to be used for the Eiffel Tower. The teams of engineers, technicians and supervisors that made the construction of these large viaducts possible are the same ones who were to work on the Eiffel Tower as well.
Forms appropriate for the wind
The design of the form of the Tower, with its curved arrises, has a lot to do with an accident at a construction site that Gustave Eiffel ran. The night of January 26, 1884, a violent gust of wind hurled the deck of La Tardes Viaduct down the valley. This viaduct was under construction at the time. Eiffel and his engineers then realized that the wind pressure on metal structures may be significant, even when the openwork is very airy. The lesson was learned for the design of the Eiffel Tower three months later.
The Eiffel Tower is the direct heir of the large metal viaducts and their high metal pylons. It uses the same design of the lattice structures, the same methods for assembling components, the same general forms, and the same design and construction teams. A daring 300meter extrapolation of the pylons that support these large viaducts!
Bertrand Lemoine is an architect, engineer and historian. He was a research director at the CNRS and general manager of the Atelier International du Grand Paris. He is an internationally recognized specialist in the history and current events of architecture, construction, the city and heritage in the 19th and 20th centuries, particularly in Paris, Greater Paris and the Eiffel Tower. He is the author of forty-three books and several hundred articles on these subjects. He is currently a consultant on architectural, urban, digital and energy issues.