STRUCTURES

1. STRENGTH AND STRUCTURES

STRENGTH/FORCE: Is all that can deform a body or modify its state of movement or rest.

STRUCTURE: is the group of elements of a body that are bound to support the effects of the strengths that act over it. The structure keeps the body from breaking or deforming in excess.

Structures have to be resistant and stable.

The first structures were made of wood, then man also used stone. Nowadays we use concrete and iron

2. EFFORTS/STRESS

If one or several strengths act over an element of a structure, the element will experiment an internal tension. This internal

tension is called effort/stress.

2.1 Different kinds of EFFORTS/STRESS

TRACTION/TENSILE

COMPRESSION

FLEXION/BENDING

TORSION

CUT/SHEAR

TRACTION/TENSILE

THE ELEMENT OF A

STRUCTURE

STRETCHES

COMPRESSION

THE ELEMENT OF A STRUCTURE

CRUSHES

FLEXION/BENDING

THE ELEMENT OF A STRUCTURE

BENDS

TORSION

THE ELEMENT OF A STRUCTURE

TWISTS

CUT/SHEAR

THE ELEMENT OF A STRUCTURE

IS DIVIDED IN TWO PARTS

Efforts activities Which efforts are applied in the following

examples?

AB

C

D

E

F

Which efforts are applied in the following examples?

AB

C

Image Structure Effort

A Cable Traction

B Shock absorber Compression

C Rope guide Traction

D

E

Image Structure Effort

D Column Compression

E Bridge Flexion

• Which efforts are applied in the following examples?

Image Structure Effort

F Nut Torsion

G Rivet Shear

F G

• Which efforts are applied in the following examples?

CHECK DIFFERENT TYPES OF EFFORTS

Image Effort

1

2

3

4

5

6

CHECK DIFFERENT TYPES OF EFFORTS

Image Effort

1 traction

2 flexion

3 compression

4 flexion

5 compression

6 traction

3. STRUCTURAL ELEMENTS

These are the most common elementsthat can be found in a structure.

• Foundations • Columns• Girders • Arches• Traction bars(Cables)

Foundations are the base of any building and they are situated under the ground and made of concrete

concrete

Girders are horizontal bars that receive flexion efforts

Foundation

Column

Girder

Forces

Columns are vertical bars that receive compression efforts

Arch: A semicircularshape that joins thegap between twopillars.

Traction bars:Cables or bars whichsupport traction efforts.

As we know, a structure has to be resistant.

A resistant structure keeps its shape whenforces are applied.

4. RESISTANT STRUCTURES

The triangle is the only geometric shape that cannot be easily deformed by applying forces to any angle.

4.1 THE TRIANGLE

The use of triangular structures is very interesting because they are very resistant, light and easy to construct.

crane pylon

Triangulation makes it possible to transform shapes into a combination of triangles and therefore makes them non-deformable.

Examples of triangulation are seen all around us especially in the construction industry (building and civil engineering).

Some examples are shown below. Look carefully how numerous triangles make each structure.

Add bars to these structures to form triangles and make them non-deformable.

The arch is another resistant structure that provides resistance to structures by distributing the effort that structure supports.

4.2 THE ARCH

5. STABLE STRUCTURES

Structures have to be stable.

A structure is stable if it keeps its position when forces are applied.

Stability is obtained by distributing the mass evenly.

Mass centre evenly distributed

Mass centre unevenly distributed

The mass centre is where all the weight is concentrated

He has the mass centre evenly distributed

When the mass is not evenly distributed, you can stop the object from falling in different ways, such as increasing its hold to the ground.

hold

6. TYPES OF ARTIFICIAL STRUCTURES

• Massive: a great concentration of material predominates

• Vaulted: Arches, vaults and domes are important holding and supporting elements

arches vaultsdomes

• Sub-frame: made up of timber (wood), steel or concrete intersecting elements.

The structural elements are: girders, pillars or columns, and foundations.

Foundation

Column

Girder

Forces

• Triangulated: Made up by linking many triangles forming flat or spatial networks.

crane oil rig pylon

• Suspended: They are held by cables

REVISION ACTIVITIES

1 EffortA door knob

An arch

A pen tip when you write

A screwdriver when screwing

The cable of a suspended bridge

A lintel

Scissors

the cord of a blind

Pedal axes

Girders on a bridge

EffortA door knob TORSION

An arch COMPRESSION

A pen tip when you write COMPRESSION

A screwdriver when screwing TORSION

The cable of a suspended bridge TRACTION

A lintel FLEXION

Scissors SHEAR

the cord of a blind TRACTOIN

Pedals TORSION

Girders on a bridge FLEXION

2. Name the effort in each of the following objects

ACB

C D E

3. Which of the following structures will support efforts best? Why?

4. Which structure is more stable?

5. Which of the following shapes are non-deformable? What can we do to make the other shapes non-deformable?

working arm

cables

base

weight

mast

6. Indicate the efforts that the following parts of the crane are subjected to.

working arm

cables

base

weight

mast

working arm cables base mast weight

FLEXION TRACTION COMPRESSION COMPRESSION TRACTION

7. Draw this bridge and indicate where the main efforts are.

Compresion Compresion

Flexion

Flexion