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Building stability |
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| Do you ever wonder how tall skyscrapers like the Empire State Building, or long suspension | |||
| bridges like the Golden Gate Bridge, or huge dome roofs like the Superdome are built so | |||
| that they do not collapse under their own massive weight? In this lesson you will see how | |||
| structural engineers decide on the optimum combination of design and materials to build | |||
| stable structures like these for the least cost. | |||
| Structural stability | |||
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"Or I'll huff and I'll puff and I'll blow your house down." The three Little Pigs |
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| The previous two lessons demonstrated how the structure of space contributes to the | |||
| remarkable geometric properties of regular polyhedra and the packing together of atoms in | |||
| elements and minerals. Basically it involves building stable structures as efficiently as | |||
| possible. Similar principles are at work in the design of man-made structures. | |||
| You have probably heard the tale of The Three Little Pigs and the big bad wolf. The first | |||
| little pig built his house from straw, which the wolf blew down and then ate him. The | |||
| second little pig built his house from sticks, which the wolf also blew down and then ate | |||
| him. But the third little pig used bricks to build his house, which the wolf could not blow | |||
| down. So the wolf entered down the chimney, fell into a pot of boiling water, and the pig | |||
| ate him! In engineering terms the smart little pig matched the structural material's physical | |||
| properties with its intended application - being stable enough to withstand the puffs of the | |||
| big bad wolf. The other two little pigs evidently did not anticipate this kind of load when | |||
| they designed their houses and paid for that mistake dearly. Lives are also at stake when | |||
| an engineer designs a massive structure like a bridge or a building. She or he must | |||
| anticipate all of the potential forces that might try to "blow the house down", so to speak, | |||
| including the unexpected ones like "wolf puffs". Then the engineer designs the structure to | |||
| be stable, that is, not to break or fall down when it is exposed to the worst possible load | |||
| that is anticipated. | |||
| The stability of man-made structures depends on two things mainly - the strength of the | |||
| individual structural materials (e.g. straw, wood, brick), and the way that they are arranged | |||
| together to form the structure (e.g. bundled, nailed, mortared). In Structure Matters we | |||
| showed how the atoms of crystals are arranged to give them the stability to maintain their | |||
| shape against both external and internal forces acting on them. Without that inherent | |||
| stability elements could not have survived intact during the fiery conditions present during | |||
| the formation of the earth. And they would not be strong enough to hold together exposed | |||
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Back to Knowhere |
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