Comparaison entre le sommet de 1889 et l'actuel

Why does the Eiffel Tower change size?

Wednesday 3 February 2021

Modified the 03/02/21

Everything you ever wanted to know about how and why the Eiffel Tower changes size.

Over its 131-year history, the Eiffel Tower has gotten taller thanks to radio and television antennas. But in addition to this new equipment added at the top, its metal structure gains or loses a few centimeters throughout the year. We’re here to tell you all about it!

The world's tallest tower for 42 years

When it was inaugurated for the Paris World's Fair on March 31, 1889, the Eiffel Tower, originally called "The 300-meter Tower," had a total height of 312 meters, making it the tallest tower in the world! It proudly held that title until 1931. That year, it was dethroned by the Empire State Building (381 meters).

Since then, the Eiffel Tower has continued to grow and today measures 324 meters including the antennas that were successively added at the summit, in 1957 and 2000, to broadcast radio and television. And it may not be over yet...

A few centimeters gained in summer, but lost in winter!

One of the reasons the Eiffel Tower is still as dazzling as ever is because it adapts to its environment and all types of weather conditions: wind, cold, rain, snow, frost, heat, etc. Like any metal, puddled iron is sensitive to variations in temperature and so reacts to high temperatures in summer and low or even negative temperatures in winter.

When temperatures rise, the Tower increases in size! This is a natural physical phenomenon called thermal expansion. Heat causes an increase in volume that makes the Eiffel Tower a few centimeters taller. This expansion also causes the Tower to tilt slightly away from the sun. The sun only hits one of the 4 sides of the Tower creating an imbalance with the other 3 sides, that remain stable, thus causing the Eiffel Tower to lean. In this way, the sun’s movement over the course of a clear day can cause the top of the Tower to move in a more or less circular curve measuring approximately 15 centimeters in diameter.

Conversely, when cold winter weather arrives, the metal structure contracts and it can lose a few centimeters as well!

Suffice it to say that these changes are natural and infinitesimal and have no impact on the robustness of the structure. They are also absolutely imperceptible to visitors and observers. On the other hand, high winds can cause it to wobble or vibrate somewhat, without damaging the structure. Because the engineers at Eiffel’s company had 20 years experience designing metal viaducts, the Tower was truly (with its curved shapes and edges) designed to minimize wind resistance! But of course, when the wind exceeds certain limits we close the top floor, or even the whole Tower, to protect the public and our staff from the risks posed by turbulent weather conditions. 
 

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