Secrets of the Eiffel Tower

Katie Leiby | May 12, 2011

The Eiffel Tower in Paris has long outstood its predicted twenty-year lifespan. Photo courtesy of Jack Linshi.

Held 100 years after the French Revolution, the 1889 Exposition Universelle, the World’s Fair held in Paris, especially was notable. It was a time to celebrate the liberty established by the republican government and to showcase recent scientific advancements. To mark the occasion and demonstrate the glory of France, a great iron tower over 1,000 feet tall would be erected on the Champ de Mars for 20 years. And thus, the Eiffel Tower was conceived.

However, from the very beginning, the stability of Gustave Eiffel’s design for the tower was challenged. Even though Eiffel was already a renowned engineer, celebrated for his work on structures such as the Garabit Viaduct, the dome of the Nice Observatory, and the Statue of Liberty, some claimed that it was an impossible feat to build a tower that could withstand the wind at such high altitudes. One French mathematics professor even argued that the tower would inevitably collapse at a height of 748 feet. How, then, has the tower, still standing at 1,063 feet, persisted for over 100 years?

The answer to this enigma came from a study commissioned by the Eiffel Tower Operating Co. to improve their maintenance procedures. Specialists from the Technical Centre for Mechanical Industries (CETIM) created a computer simulation program in order to analyze the durability of the tower after wear from weather conditions and every day operation; the tower has millions of visitors each year. They began gathering preliminary data on the current condition of the tower’s structure through mechanical and chemical tests and then analyzed the effects of physical laws on different elements of the tower, including individual structural features, decorations, and elevators. One aspect in particular to be studied was the puddled iron from which the tower was built.
Puddled iron, a nineteenth century material that behaves differently from the steel used in most buildings today, holds the key to the Eiffel Tower’s resilience. In the puddling process, impurities are burnt out of pig iron through the aid of iron oxides and a current of air through the furnace. The purified iron was collected in balls before being squeezed and hammered out. Also forming the original framework of the Statue of Liberty, this type of wrought iron is readily able to accept protective coatings and capable of withstanding corrosion and fatigue.

The behavior of puddled iron was just one of the many factors that the experts at CETIM needed to consider when creat-ing their model of the Eiffel Tower. Original data from Eiffel’s blueprints and notes from later maintenance procedures were also incorporated to create an extremely complex model of one million variables which takes into account the 18,000 individual iron parts, 2,500,000 rivets of the tower, and the load in all directions. The total framework of the tower itself weighs about 8,050 tons. With additions such as elevators and restaurants, the total weight of the tower is now 11,130 tons.

Yet because of all his experience, Eiffel was confident in the sturdiness of his design and his planned methods of construc¬tion for the 1063-foot tower. For example, he intricately designed the tower’s foundation, which is composed of cement and stone placed at an exact angle so that each of the four curved piers of the tower with an inward tilt of 54° would maximize wind resistance and exert a perpendicular thrust to its foundation. In addition, the legs of the tower rested on sand boxes and hydraulic jacks during construction so that the metal beams at the tower’s first platform could be leveled within one millimeter of the horizontal plane, a crucial step for ensuring a safe base for the remainder of the tower.

And the tower certainly stands soundly thanks to these details. The CETIM’s model suggests that the Eiffel Tower will last for at least two or three hundred more years. Simulated precipitation, temperature, and extreme wind conditions are projected to have little effect, and even doubling the weight of the tower, though causing it to “move,” will still leave it safely standing. The rising temperatures caused by global warming may pose problems for the structural integrity of the tower in the future due to the expansion of iron upon heating, but for now, experts conclude that the Eiffel Tower is here to stay.