# Structures

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25 Νοε 2013 (πριν από 4 χρόνια και 7 μήνες)

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Structures

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Contain the essential parts

Span a gap

Protect the contents

Support something

What does a structure do?

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Categories of structures

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Types of structure

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When loads are placed on a structure,
forces

begin to act
on it and through it. These forces are either
static

or
dynamic
.

Static forces:

do not move

stationary

do not change

(e.g. bricks in a bridge).

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Dynamic forces:

will move on a structure

can change in size.

By sitting up and down this
man is creating movement
in the chair structure,
placing the chair under

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All structures have

applied to them. They must also
be designed to cope with the
forces

acting on them
without permanently changing shape or breaking.

Forces within a structure

The size of a force (the load) is measured in
newtons (N)
.

There are five main types of force:

Compression

Tension

Bending

Torsion

Shear.

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Forces within a structure

compression

Compression is a squashing or pushing
force.

When an object is compressed,

the
external

force applied pushes
downwards, squashing it.

To compensate against this, the
internal

forces inside the object are pushing out
against the external force.

The object is safe as long as the internal
force is equal to or greater than the
external force. However, when the
external force is greater than the internal
forces, the object will fail.

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Forces within a structure

tension

Tension is a pulling or stretching force.

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The force is at an angle to the shelf, making the shelf
bend. This causes compression in the top half of the shelf
and tension in the bottom half.

Forces within a structure

bending

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Forces within a structure

torsion

Torsion is a turning or
twisting force.

This spanner is turning a
bolt.

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A shear force is a sliding force, pulling in
opposite directions

Forces within a structure

shear

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Designing strong structures

Stability

why things don’t fall over!

All structures need to be
stable
.

Stable structures are not likely to move beyond
the limits they were designed for.

Look at the structures below.

What makes these structures stable or unstable?

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Triangulation

No
triangulation

Designing strong structures

The triangle

making structures rigid

Unstable structures can sometimes be made more
rigid by adding triangles to the shape.

Force

Force

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Beams and bridges

A beam
spans

a gap and enables

to be carried
across. It consists of a straight
bar

or
girder

supported at
both ends.

When a beam is only supported at one end,

it is called a

cantilever
.

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Beams and bridges

A bridge works like a complex
beam

many parts. There are four basic types of bridge:

beam

arch

What sort of bridges are these?

cantilever

suspension.

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Describe it

Describe each of the structures above.