lunes, 7 de febrero de 2011

1º ESO STRUCTURES

A structure is a group of elements somehow united to support a load with stability. Examples of structures are  bridges, electricity pylons or dams. Can you think of others?.
Well, you'll probably think of tall buildings or long bridges, but there are also other examples such as chairs or tables that  we use every day. Even an egg has a structure.
In the image on the left, a modem skyscraper with two main structure
a) A skeleton, or frame, made of steel.
b)  The “skin of the skyscraper " is the walls that are made of glass panels and thin concrete sheets.

 All structures must be capable of withstanding the loads and forces for which they are designed. This does not however mean that they must always be rigid; some structures are designed to be flexible. Flexible structures are often more able to withstand dynamic forces. These are forces that change direction and quickly become more intense. Buildings, such as those built in earthquake regions of the world, can be made flexible.

Structures classifications: Shell structures and Frame structure

A shell structure is one in which the strength reloads into the outer surface.  They are usually lighter than frame structures. For example, A turtle, an egg, an airplane, a boat,  a lobster or a car has a shell structure .
In a structure the form is very important.  The resistance of the structure depends on its form.  A good example is an egg.

Test:  Get an egg and place it vertically between your index finger and your thumb.  Now squeeze hard.  You will see that however hard you squeeze, you will not be able to break the egg.  You can even do it with both hands, by interlacing your fingers and squeezing the egg between them so that force is applied at both the lower and upper ends of the egg.
Sometime we use objects that are a combination of both structures.  An example is a Chair.   There is  a tubular steel frame structure ( whose function is to support the load ) and a shell structure ( piece of wood, plastic or metal  which you sit on ).

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