Eiffel Tower is a monumental construction in France, Europe. Societe d'Exploitation de la Tour Eiffel dates it to 1887-1889. Its height is listed as 330 m (estimated). Societe d'Exploitation de la Tour Eiffel also records: “Exhibition tower.”
A wrought-iron lattice tower assembled from 18,000 parts in about two years.
What makes it extraordinary
Thermal Expansion and Solar Alignment
The tower's wrought-iron structure is subject to significant thermal expansion depending on ambient temperatures. As the sun heats one side of the monument, the metal expands, causing the top of the tower to shift away from the sun by as much as 18 centimetres. This physical movement demonstrates the elasticity and environmental responsiveness of the lattice design, which must accommodate both the heat of the sun and the pressure of the wind while maintaining its structural integrity.
Commemorative Scientific Engravings
To counter artistic protests against the tower's industrial aesthetic, Gustave Eiffel engraved the names of 72 prominent French scientists, engineers, and mathematicians on the structure. This 'invocation of science' served to emphasize the tower's purpose as a monument to modern industry and progress. Although these names were painted over at the start of the 20th century, they were fully restored in 1986–87 by the tower's operating company, maintaining the original tribute to the intellectual contributors of the era.
Material Composition and Structural Weight
The Eiffel Tower is primarily constructed from 7,300 tonnes of puddle iron, also known as wrought iron. Over time, the addition of modern amenities such as lifts, shops, and broadcasting antennae has increased the structure's total weight to approximately 10,100 tonnes. Demonstrating the efficiency of its lattice design, if the original 7,300 tonnes of metal were melted down, it would fill the tower's 125-metre square base to a depth of only 6.25 centimetres, assuming a standard metal density of 7.8 tonnes per cubic metre.
Aerodynamic Design and Wind Resistance
Gustave Eiffel prioritized wind resistance as the primary design concern, utilizing graphical methods and empirical evidence rather than standard mathematical formulas to determine the tower's strength. The resulting exponential shape and the curvature of the four outer edges were calculated to ensure that wind pressure at any point was counteracted by the tension between structural elements. The tower is so robustly overdesigned that it sways only up to 9 centimetres in high winds, despite its massive 330-metre height.
Subterranean Foundation Engineering
Construction began on January 28, 1887, with foundations that varied by proximity to the river Seine. While the east and south legs rested on simple concrete slabs, the north and west legs required more complex engineering due to their location near the water. Workers used compressed-air caissons, measuring 15 metres long and 6 metres in diameter, driven to a depth of 22 metres to support 6-metre-thick concrete slabs. These slabs were topped with limestone blocks and anchored by 7.5-metre-long bolts.
Evolution of Hydraulic and Electric Lifts
Equipping the tower with lifts was a major engineering challenge because the legs' curvature prevented straight tracks to the second level. The original 1889 system included Roux, Combaluzier & Lepape chain-driven lifts and Otis hydraulic rams. In 1899, these were replaced by Fives-Lille lifts with compensating mechanisms to keep floors level during the changing angle of ascent. By 1986, the system was automated with a computer-controlled, oil-filled hydraulic system, though the original water hydraulics were retained as a counterbalance.
Precision Engineering and Off-Site Fabrication
The construction of the tower relied on extreme mathematical precision, with the drawing office producing 1,700 general and 3,629 detailed drawings for 18,038 distinct parts. Rivet hole positions were specified to within 1 millimetre, and angles were calculated to one second of arc. Because of this exacting preparatory work, no drilling or shaping was performed on the Champ de Mars; any component that did not fit perfectly was returned to the factory in Levallois-Perret for alteration before being joined by 2.5 million rivets.
Hydraulic Alignment and Scaffolding
During the critical stage of joining the four legs at the first level in March 1888, engineers employed specialized techniques to ensure perfect alignment. The legs were intentionally constructed at a slightly steeper angle than required, supported by sandboxes on timber scaffolding. To allow for minute adjustments, hydraulic jacks capable of exerting 800 tonnes of force were fitted to the shoes at the base of each leg. This allowed the massive iron cantilevers to be precisely positioned before being permanently joined.
Global Height Records and Changes
Upon completion in 1889, the Eiffel Tower became the tallest human-made structure in the world, surpassing the Washington Monument. It held this title for 41 years until the Chrysler Building was finished in 1930. While it lost the title of tallest structure, it regained height superiority over the Chrysler Building in 1957 with the addition of a broadcasting aerial. As of 2022, the tower stands at 330 metres following the installation of a new digital radio antenna, remaining the tallest freestanding structure in France.
Scientific Utility and Preservation
Originally intended as a temporary structure for the 1889 World's Fair, the tower was slated for dismantling in 1909. It was spared primarily due to its utility in scientific research, including Gustave Eiffel's meteorological observations and air resistance experiments. Its role in early 20th-century radio telegraphy proved decisive; the tower became part of the International Time Service in 1910 and housed a wireless station that intercepted critical German communications during World War I, including intelligence that led to the arrest of Mata Hari.
