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Aug 03, 2009 Autoplay When autoplay is enabled, a suggested video will automatically play next. Up next Lego 21019 – Building the Eiffel Tower – Stop Motion - Duration: 4:46.
Eiffel Tower Photo by / Wikimedia, modified by Aatish BhatiaTo understand Eiffel's ingenious design, let's start with a little puzzle. Imagine that someone melted all of the iron in the tower into a solid ball. How big do you think that ball would be? (Click on the image to enlarge.)Each of the balls shown in the image are drawn to scale, next to their diameters.Before reading any further, take a moment to guess your answer.The correct choice is D ( to prove it). If you melted all the iron in the Eiffel Tower into a ball, it would be just 12 meters (less than 40 feet) in diameter. The tower's immense height (324 meters, or over a thousand feet) belies the fact that it's incredibly light for its size. To see it another way, if you were to melt the Eiffel Tower's iron into a rectangular block as big as its base, then that block of iron would be only 6 centimeters (2.4 inches) tall.
It wouldn't even be visible in the image above. Eiffel Tower Photo by / Wikimedia, modified by Aatish BhatiaOne last way to picture the Eiffel Tower's lightness. Imagine the smallest cylinder that completely wraps around the Eiffel Tower.Now think about this. The air in this tube outweighs all the iron in the tower. (Don't take my word for it,.)So how did Eiffel design a structure that's strong enough to withstand the elements, and yet weighs about as much as the air surrounding it?The secret lies in understanding the shapes of strength. It's a lesson we can learn by looking inwards.
By studying our bones, we can discover some of the same principles that Eiffel used in designing his tower. / Nature MaterialsNow let's zoom into the crust of that bone baguette - the compact bone. It's made up of tiny tubes called osteons, each just 2 tenths of a millimeter across, with a blood vessel running down the middle. Zooming further into the walls of these osteons, we find that they're made out of tinier bundles called fibrils. Zoom further still, into one of these fibrils, and we see that they're really a bundle of fibers, and each fiber is really three interwoven strands. Pull these strands apart, and we've unweaved our bones into its most fundamental unit, a long chain-like molecule called.This fractalesque way of putting things together, building with materials that are self-similar as you keep zooming in, is known as structural hierarchy.
And it's this structural hierarchy - tubes within tubes within tubes within tubes - that gives our bones their lightweight strength. (The spongy bone also has a fractalesque, self-similar design. If you look at a piece of it under an electron microscope, you'll find that it looks.). / Nature MaterialsBamboo exploits the same idea. This ultra-fast growing grass needs a way to minimize material and stay very light, so it can grow tall and not collapse under its own weight. Bamboo's hollow tube shape is a very efficient way to create stiffness. And like bone, bamboo is made out of tinier tubes, which in turn are made out of bundles of fibers, that are each made of out even smaller bundles of fibers, and so on.
When you unweave a bamboo down to its tiniest thread, at the scale of a nanometer, you arrive at another long chain-like molecule -.Bamboo and bone are both natural nano-engineered materials that use structural hierarchy to achieve their lightness and strength. The Eiffel Tower uses a similar idea. Eiffel borrowed this notion from bamboo and bone (although he probably arrived at it independently), and put it to use on a colossal scale.Like many modern structures, the Eiffel Tower uses an arrangement of criss-crossing 'X-shaped' beams known as a truss. This is a to engineer structures by relying on the inherent strength and stability of triangles. If you zoom into one of the Eiffel Tower's trusses, you'll find that they aren't as solid as they seem - each of them are made up out of smaller, similar trusses. The material has more holes than it has iron.
This hollow form contributes to the tower's mind-boggling lightness. The next time you go over a bridge, look carefully, and you're likely to see the same idea at play. Eiffel Tower Photo by / Wikimedia, modified by Aatish Bhatia Shaped by the WindOnce you've figured out how to build a lightweight tower, how do you ensure that it stays standing? The Eiffel Tower has to contend not just with gravity but with the considerable toppling force of the wind.
To counter this, its sloping curve closely follows the most efficient shape for resisting the wind.The trick to building a well engineered structure lies in transferring the forces from where you don't want them to act to where you want them to act. Eiffel understood this. The shape of his tower has the special property that the combined force of the wind and the tower's own weight will flow down the legs of the tower, all the way down to the strong foundations.
(In physics terms, the tower has so that the torque, or toppling tendency, generated by the wind is balanced by the torque due to its own weight.)In where he responds to his art critics, Eiffel describes this idea. Figure from On Growth and Form by / Public DomainOn the left is a drawing of the push and pull forces in. And on the right is a similar drawing of push and pull forces in the top of the thigh bone (the femur). These images, adapted from Culmann and Wolff's publication in 1870, represent the first collaboration between an engineer and an anatomist.So when Culmann saw the pattern of the spongy bone in the top of the thigh bone, it reminded him of his crane.
He was immediately struck by how clearly he could see the criss-crossing lines of forces in the bone. / Public DomainThe spongy interior of your thigh bone is efficiently arranged so that the material is present where the forces are the greatest, and absent where there aren't any forces. In bone, this process occurs gradually over its development. The spongy bone hardens and aligns in directions where it experiences the greatest force, and atrophies in places where it isn't used. There's an analogy here to how those impressive sandstone arches are. The wind carves away places where the stone is least stressed, leaving in place a three dimensional outline of the lines of force, where the stone is most densely compacted.In recent years, the mathematical exactness of this has been.
But the general principle, that bone adapts to its functional demands, and that bone structure corresponds to the forces it experiences, is still widely accepted.What does this have to do with Eiffel? Well, Culmann's approach of graphically representing the push and pull forces was a powerful new tool, one that's still used today. One of Culmann's students, Maurice Koechlin, worked for Eiffel.
And it was Koechlin who of the Eiffel Tower, drawing from his training in visualizing forces. The same tools that Culmann developed and used to understand bone were later used by Eiffel's engineers to design a tower that.