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Bridge Design (and Destruction!) Part 1
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Bridge Design (and Destruction!) Part 1
When was the last time you had to do this?
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Or this, to get across a stream, river, fjord, or lava pit?
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Probably never, because we have these things called bridges.
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Bridges are awesome!
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But what are all these different types of bridges that you see around?
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Why don't they all look the same?
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Let's find out!
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Engineering!
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The most basic type of bridge is a beam bridge.
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It has the most simple design, with a beam, also called the bridge deck, that is supported
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at both ends.
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Let's drop into our diagram mode to see how the forces act upon this bridge.
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When a load is applied to these bridges, they bend and experience two types of forces.
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The top of the beam is pushed together, which is called compression.
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The bottom of the bridge is pulled apart, which is called tension.
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Here we are using lasers to build model bridges out of balsa wood and plywood.
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Always wear purple gloves while handling balsa wood.
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Safety first, kids.
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You can see the simple design.
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Now let's see what happens when we apply forces to it.
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To do this, we'll use a compression tester that
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can apply up to 20,000 pounds of force, although we probably
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won't get that high in this test.
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The compression tester will apply a load, or in other words, a weight,
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and measure the strain, which is how far the material moves in response to a load.
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Also to help us on this test will be these LEGO people, who will measure the ability
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to be launched from a bridge when it breaks.
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Critical information for bridge designers.
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Officer?
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Hello.
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You see that as the load increases, the bridge bends, and it eventually breaks at a load
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of 115 pounds.
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And now, what if you want to span a longer distance?
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Here we use the same deck material on top, but we have doubled the length of the bridge.
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This time, our main test subjects will be the happy farmer chef, hat man, bike guy with
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no helmet, shame on you.
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You can see that the longer bridge bends even more, and it breaks at a much lower load,
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only 25 pounds, which is 80% weaker than the short beam bridge.
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Plus, the LEGO people get launched into space.
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That isn't very good.
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We want the bridge to support a lot of weight over a long distance.
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So how can we make bridges that span longer distances?
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There are other bridge designs that allow us to use the same deck material
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and span longer distances.
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This takes us to the curviest of bridges, arch bridges.
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An arch is a great way to evenly distribute a load and has been used in bridge building
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for a long time.
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In this example, we just have a beam bridge with an arch underneath.
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The load is distributed through the arch into the ground.
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Notice how only compressive forces are present and no tension forces.
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This is great for wood and stone bridges because they are much stronger in compression than
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tension.
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On our model arch bridge, we used the same long bridge length, with added arch supports
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on both sides.
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To help us is Tricycle Man, Helmet, Good Job, Classy Business Woman, and this crazy guy.
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Let's go!
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You can see that the beam does not bend as much with the arch underneath, and that reaches
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a higher load before it fails, 100 pounds, which is 500% stronger than the long beam
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bridge.
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Here we have seen that beam bridges get weaker as they get longer.
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Adding an arch makes the bridge very strong, but arches have length limitations.
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Beam and arch bridges historically have relied on wood and stone as building materials.
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These materials are usually only strong in compression and not in tension, which restricted
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the designs that could be used.
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However, with the discovery of steel, bridge builders now had the ability to add structural
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units that would be strong in tension.
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This led to more intricate styles of bridges that we will explore in our next video.
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- Idioma/s:
- Etiquetas:
- EducaMadrid
- Autor/es:
- MITK12Videos
- Subido por:
- Samuel E.
- Licencia:
- Reconocimiento - No comercial - Compartir igual
- Visualizaciones:
- 91
- Fecha:
- 30 de octubre de 2013 - 17:25
- Visibilidad:
- Público
- Centro:
- IES JOAQUIN ARAUJO
- Duración:
- 05′ 08″
- Relación de aspecto:
- 1.78:1
- Resolución:
- 640x360 píxeles
- Tamaño:
- 16.43 MBytes
