 |
 |
||
 |
|||
FIGHT AGAINST GRAVITY #1 Excerpt from "The Art Of Construction" by Mario Salvadori
All structures, in a one-family house or a skyscraper, in an arch or a suspension bridge, in a large dome or a small flat roof, are always either in tension or in compression. Structures can only pull or push. If you understand how tension and compression work, you understand why structures stand up.  How do we recognize tension and compression? We cannot always put our arm where the structure is and "feel" these forces, but it is still quite easy to recognize them. Take a thin rubber band and pull it with your hands. You are putting the rubber band in tension and the band becomes longer.  You know that whenever a part of a structure becomes longer it is in tension. Take a rubber sponge and push on it: the sponge becomes shorter in the direction in which you push. Whenever a part of a structure becomes shorter, it is in compression.There is a catch to recognizing tension and compression simply by the lengthening and shortening part of a structure, and you probably have noticed it already. The amount of lengthening and shortening in a structure is usually so small that it is not possible to see it with the naked eye. ...if you imagine putting your arm where the structure is, most of the time you can guess how it would feel and whether it is in tension or compression. If you are in any doubt about compression in an arch bridge, stand 2 feet away from a wall and lean on it, with your hands up against the wall and your body bent toward the wall. You are now half an arch and you will feel the compression.  If you and one of your friends put your hands on each other's shoulders and move your feet away from each other, you will become a full arch and feel compressed by each other's weight. But if your shoes slip on the floor you begin to slide apart, the arch will collapse. Its ends must be firmly anchored to prevent it from spreading apart.Fight Against Gravity 2 |
|||
 |
|||
 |
|
|
|