Science and Engineering in Derby and Derbyshire
So there you are. In the city of romance, fashion and copious amounts of stinky cheese. Beautiful Paris, and sat looking at one of civil engineering’s greatest creations. Sadly you aren’t sharing this touching moment in the warm Parisian sun with a Gyllenhaal of choice, but rather a box of used matches. Luckily you are a plucky sort, dear reader, and you set about using the matches in that most British of pursuits: making a scale model. You have a lot of matches so you proceed to making it 1:1, which is going to take a few days. You measure. You plan. You build. Unfortunately by day three it is abundantly clear that your 1:1 is more of a 0.95:1. So you change the plans and build a little more. You complete, but it’s too big. Then too small. So before you go slowly mad on La Rive Gauche what is going on?
First let’s examine the tower itself… Designed originally for the 1889 World’s Fair, as possibly the most gigantic entrance gate possible, the sides decorated with the names of 72 great scientists such as the mathematician Poisson and chemist Lavoisier, it was supposed to be removed twenty years later. However, though engineers are some of the best people at killing their darlings (the practice of throwing away the piece of work that you like the most because it generally is too pretty and over-inflated) Gustave Eiffel wasn’t going to let his tower go. He installed a laboratory on the third floor for meteorology, and the laboratory and the tower itself were used for a number of experiments from pendulums to wind tunnels. The science that really saved it though was that new fad in the early 20th century, telegraphy. By 1899 the tower had sent waves across the channel and in the 1910s it was adopted by the military, just in time for World War One. By the 1950s the Eiffel Tower allowed Parisian Anglophiles watch the wedding of Princess Elizabeth, and the tower still today serves for some transmissions (though most have been shifted to digital). Of course what makes Le Tour perfect for this job is its size. Containing 7300 tonnes of iron and 2,500,000 rivets the tower is huge.
So why is it proving to be such a measuring problem? Standing nominally at 300m tall (324m if you include the antennae) the Eiffel Tower has something of a growing, and shrinking issue, depending on the weather.
Thermal expansion causes some modification in size of solid objects when the temperature changes, because the particles that make up the construction materials move about. When heated the particles get all excitable and they move away from one another, rather like a particularly good disco, some orbit around the bar, others on the dance floor. Then when cooled they slow down and get all friendly again. Its a problem that all architects have to overcome when designing everything from magnificent towers, to less than magnificent housing estates. Or rather a problem that the civil engineers have to overcome
Unless you observe your house very very carefully you probably wouldn’t notice this happening. In the Eiffel Tower the change is around about 15cm, from a distance not seen, but if you happen to be carefully and closely observing that’s enough of a difference to be seen.
If you want to know more about the Eiffel Tower and its construction you can here. For an overview of how thermal expansion effects a very popular modern building material-concrete:
Uygunoğlua and Topçub “Thermalexpansion of self-consolidating normal and lightweight aggregate concrete at elevated temperature”