Science Saved the Eiffel Tower

Eiffel Tower Night.jpg
Via Flickr user Gadjo_Niglo

With more than 7 million visitors each year the Eiffel Tower is the premier tourist attraction around the world, but back in the late 19th century it was almost demolished on multiple occasions. The key to its survival was the scientific usefulness the structure possessed. 

Design

As I leave Paris, one of the standout experiences was reaching the summit of the Eiffel Tower due to its impressive engineering and advanced construction, and the scientific experiments which it facilitated. The 300 m high tower dominates the antique city buildings of Paris and from its construction in 1889 it was the world’s tallest building for 40 years. 

Alexendre – Gustave Eiffel entered the design into a competition for the 1889 world’s fair. The French government wanted to mark the centenary of the French Revolution with a structure that would wow the world. Against more than 100 competition designs, Gustave Eiffel won partly due to his persuasion, passion and previous structural achievements which include the metal framework for the Statue of Liberty and a moveable observatory dome in Nice.

The design described a four legged, open lattice structure that ascends and transforms into a single leg. The four legs are equidistant at 125 m apart. The tower consists of 18,000 girders connected with 2.5 million rivets. There are three levels accessed via elevators designed to scale the curved legs. Eiffel’s company drew 5,330 construction drawings for the tower’s design.

The proposed design was a testament to Gustave Eiffel’s superior knowledge of the behaviour of metal truss and arch systems under loading. He was an expert with iron and was nicknamed the “magician of iron” by many engineers. 

Construction 
 
The external forces acting on the tower vary with height, predominately due to wind forces. In the 1880’s Gustave Eiffel did not have computer simulations. Consequently, most of the tower’s components required individual calculations. 50 engineers worked for 18 months to complete the calculations before construction could begin.

Each of the 18,000 iron girders were prefabricated at the Eiffel company workshop on the outskirts of Paris and were transported to the work site using horse drawn carts. The workshop fabricated the girders to an accuracy of 0.1 mm. If components did not align to within 0.1 mm they would be sent back to the workshop and altered.

Construction lasted two years and two months which was quick considering the size and complexity of the project and the small workforce of 300. The time and precision exhibited throughout the planning resulted in a seamless construction.

 

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Eiffel Tower Construction Time-Lapse (public domain)

 

The Tower’s Saviour

“It will be an observatory and a laboratory such as science has never had at its disposal.” – Gustave Eiffel

Initially the Eiffel Tower had a set lifespan of 20 years but Gustave Eiffel would make his beloved tower a necessity for the scientific community. Soon after opening the tower, he installed a meteorological laboratory on the top level. He invited scientists from across the world to use the laboratory and conduct experiments using the tower’s height.

Radio ultimately saved the tower from demolition. In 1898, Gustave Eiffel invited the prominent scientific instrument manufacturer Eugène Ducretet to use his third floor to experiment with radio waves. By the end of that year Ducretet successfully sent a radio message 4 km to the Panthéon. This paved the way for the first radio transmission from France to the United Kingdom.

Gustave Eiffel then cunningly invited the French military to use the tower for their own research on radio transmission. From a small wooden shack at the base of the southern leg, the French military could make radio contact with forts around Paris. By 1908 the military could send messages as far away as North America and they installed a permanent radio station at the Eiffel Tower. Subsequently in 1910, the Paris city renewed the tower’s permit for an additional 70 years.

Aerodynamics

Gustave Eiffel became interested in aerodynamics during the designing phase of the Eiffel Tower project. He was unsure about the flow of air around the tower’s unique geometry. Once the tower was constructed he attached a wire from the second level and observed falling bodies over the 115 m descent. Devices measured the velocity of the objects and the air pressure. 

By attaching a flat plate which could be thrust back by the air’s pressure to the front of a falling body, he created a new measuring technique for the resistance of air on a moving body. The plate’s displacement compressed a spring and the pressure was recorded using a registering drum with a tuning fork for more accurate results. This provided the first, accurate, continuous data for pressure and velocity simultaneously up to velocities of 143 km/h.

The limited measuring equipment of falling bodies led Eiffel to build a wind tunnel at the base of the tower in 1909. The apparatus shows how air flows around stationary objects which can mimic flight. He used many of the falling body objects in this wind tunnel and was able to confirm that the drag force on a body moving through air is equal to the drag force produced by air moving past the same stationary body. Within two years, Eiffel and many leading aviation engineers conducted over 5,000 tests in the original wind tunnel. 

Conclusion

The Eiffel Tower has been a pivotal part of scientific history in the last 150 years. Fortunately for tourists today, Gustave Eiffel had the foresight to take advantage of the structures great height and telecommunication potential. Paris would be a very different city without it’s star attraction.

For those interested, feast on a detailed article in New Scientist celebrating the tower’s 100th birthday.

Eiffel Tower Ratatouille

Frengineer 2017

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