Structures

STRUCTURES

2º ESO

TECHNOLOGY DEPARTMENT

STRUCTURES EVERYWHERE!

Buildings, machines and a lot of objects we normally use, need a STRUCTURE or skeleton to hold up every piece they are made of.

We find two types of structures: NATURAL or MANUFACTURED

NATURAL STRUCTURES

Structures are not new, nature produced the first structures long before humans were able to.

A tree has to carry the weight of its own branches as well as resisting strong winds.

MANUFACTURED STRUCTURES

A manufactured structure is quite simply a structure built by human beings.

Many of Nature´s structures have been copied by humans. The shell of a snail and the body of a modern car are both shell structures

designed to protect their occupants.

When we think of manufactured structures we often think of examples such as bridges, electricity pylons and tall buildings, but some of the common structures are quite simple. Most objects resists loads, and most objects are also structures.

NATURAL OR MANUFACTURED?

Have a look to these pictures. Are they natural or manufactured structures?

TYPES OF STRUCTURESMass Structures(Estructuras masivas)

Frame Structures(Estructuras de armazón)

Shell structures(Estructuras laminares o de carcasa)

MASS STRUCTURES

Mass Structures are solid structures which rely on their own weight to resist loads. A single brick is a mass structure but so is a large dam.

FRAME STRUCTURES

Frame structures are made from many small parts (called members), joined together. Buildings, bridges, cranes and parts of this oil rig are just a few

examples.

SHELL STRUCTURES

Shell structures are made or assembled to make one piece.

Tin cans, bottles and other food containers are often good examples of shell structures, but larger things such a wash machine and aeroplane bodies are examples of more complicated shell structures.

WHAT DO STRUCTURES DO?

Support to hold something upright and steady.

Span a distance or reach across a gap.

In short, all structures do one or more of these things:

Contain or protect something.

Shape objects, machines and

buildings.

FORCES ACTING ON STRUCTURES

A structure has forces acting on it all the time. A structure must be able to resist the forces acting on it

without collapsing.

Forces can be:

Static (stationary): Static forces are usually forces caused by the weight of the structure and

anything which is permanently attached to it.

Dynamic (moving): Dynamic forces are caused by things such as wind, waves, people,

and vehicles.

FORCES ACTING ON STRUCTURES

Bend (doblar, curvar)

Pull (estirar)

Press (comprimir)

Cut (cortar)

Twist (retorcer)

Members of structures support external forces or LOADS that can act in different way. Forces can:

FORCES ACTING ON STRUCTURES

Depending on the external force or load acting on a structural member, it can be under different STRESSES (Esfuerzos)

TENSION (Tracción)

COMPRESSION (Compresión)

SHEAR (Corte o cizalladura) TORSION

(Torsión)BENDING (Flexión)

FORCES ACTING ON STRUCTURES

TENSION: The forces acting on a structural member try to pull it apart. COMPRESSION: Name given to a force that tries to squash something together.

The part of the structure that has a tensile force acting on it is called a TIE and the part that has a compressive force acting on it is called a STRUT.

TORSION: Name given to a turning or a twisting force.

SHEAR: A shear force is created where two opposite forces try to cut something in two.

BENDING: The forces acting on a structural member form a curve on it. The structural member is stretched and squashed at the same time.

STRUCTURAL MEMBERSMembers are the different parts of a frame structure.

How well a structure member resists the forces acting on it depends on: the material it is made of, its size and its shape or section.

Some of these members are:

Wires (cables): They resist tension sucessfully.

Column (columna): Is a vertical structural element that transmits, through compression, the weight of the structure above to other structural elements below.

Pillar (pilar): Is similar to column but with square shape.

STRUCTURAL MEMBERSBeams (vigas): They have to resist bending. They are made from different sections easy to remember because they are named after their shapes.

Girder (jácena): The main horizontal support of a structure which supports smaller beams. They often have and I-shape for strength, but may also have a box shape, z shape or other forms.

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RESOURCES

The information used was mainly extracted for the following web sites: