STRUCTURES
TYPES OF FORCES THAT ACT ON A STRUCTURE

1º Fill in the blanks in these statements.

(a) The two main kinds of structures are _______ and _______ structure.
(b) If a frame structure has no ‘skin’ on it, it is  called an ___________frame  structure
(c) A structure that relies upon the shape it has been moulded into to give it its strength is  called a ________ structure.
(d) Loads can be  _______ (non-moving ) or _______ (moving).
(e) Tension, compression, shear, torsion and  bending are all types of ____________
(f) All these forces must be catered for in _________structures.
(g) An object is in tension if it is being ______

(h) An object is in compression if it is being_______
(i) An everyday item that cuts using a shear force is a ________
(j) Torsion is a _________ force
(k) If a beam is bent, the top surface is in ___ and the bottom surface is in ____
(l) ____ is a force that tries to stop one surface from sliding against another.

(m) When oil or grease is added to reduce friction, it is called a _________
(n) A long, rigid piece of wood or metal used to support a load across a gap is called a ______
(o) The use of triangles to strengthen a frame is called _____
(p) A common structure often found across water is a ______
(t) Little metal balls that reduce friction and allow bicycle wheels and pedals to move smoothly are called ___

Word: Open frame, Stretching, Static, Shell, forces, Scissors, compression, Beam, Bridge traction, friction,  Designing , lubricant, frame, dynamic, twisting, triangulation, bearings

 

2º Define structure

3º Examples of structure

4º  What is a SHELL STRUCTURES. Examples.

5º  What is a frame Structure. Examples

6º A example of a _________________ is a brick in a house

7º  Write some examples of static and dynamic forces

8º  A force tending to compress or reduce something is also know as ______

9º A force tending to stretch a material is also know as _____________

10º Calculate the forces at point A and  B.

 

Activity: Copy in your notebook this structures. Which of these structures is stable and which is non-stable?. What can you do to make them rigid?.
Label the sketch to indicate a member that is in tension and a member that is in compression.	This saw blade is in tension/ compression/shear. Circle the correct answer.
The rope marked X is in shear/ compression/ tension. Circle the correct answer.	4. Name the force acting on the material shown.
Name the force acting on the fabric.	This rope is in tension/ compression/ torsion. Circle the correct answer.
The pin shown is in tension/ compression/ shear. Circle the correct answer.	Identify the forces shown in the sketch.
9. When bicycle brakes are pulled, the force between the brake blocks and the wheel is a bending force/friction force/shear force. Circle correct the answer. 10. The beam shown is bending under a load. Identify the parts X, Y or Z of the beam which are (a) in compression (b) in tension (c) neither in tension nor compression.

Dictionary:

Sketch: A simple, rough drawing, done rapidly and without much detail.

Bearings.

 

 

 

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

SHELL STRUCTURES

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 ).

FRAME STRUCTURES

They are structures that have a  skeleton associated with them.  A example are leaves   with frame structures and skin on them. If they have no   “skin” on them, they are called  “open frame”.

An  example of a natural open frame structure is the  spider’s web.

STRUCTURAL MEMBER

A structural member is a part of any  structure or building.  All structural members have a  mechanical function, so  each of them supports a force ( tension ,  compression, flexion ..).

REDUNDANT MEMBER

A redundant member is a part of a structure that  has no mechanical function, so there is no force applied to the element. So, if there are no forces, redundant members can be removed from structures.

A example in a house is a brick. If you push  down a wall in you living room to make that space bigger, the building would be affected. ( It is not a very good example, but I think you now understand what is important in a structure ).

WHAT IS FORCE?

In a structure we can define a force  as  any agent that causes stress or compression  in a fixed body:

Pull force -> Stress effect

Push force -> Compression effect

The force of gravity pulls everything downwards towards the earth. There are forces acting on us all the time
Force is measured in Newtons (N).

TYPES OF LOADS

Structures are built to support static (not moving)  and dynamic loads. For example, in a building, static load is the weight of beams, cement, glasses, etc and the dynamics loads are furniture , people, computers, tables, etc.

Dynamic loads are more important that Static loads because….. let’s see a example:

In a chair, the  design is made  to support the heaviest person sitting on it ( static load ), but if a boy start to jump on it  ( dynamic load ),  the chair is more likely to break.

TYPES OF FORCE THAT ACT ON A STRUCTURE

 

Structures are subject to the following types of forces
Tension -> a pulling force that attempts to stretch or lengthen. For example, a rope with a weight hanging on the end.	• Compression -> a pushing force that tries to squash or shorten.
Bending -> forces that attempt to cause bending deformation;	Torsion -> forces that cause twisting;
Shear -> ‘sliding’ forces that act in opposite directions. For example, in a teapot, there is a shear force in the surface between the handle and the body.  You want to move the teapot up, while the load is downwards.

 

All these forces must be taken into account in designing structures. If the designer does not consider these forces, there is a big risk of  crumbling, distortion, deformation or falling in all types of structures (bridges, buildings .. )

To prevent disaster, most structures are designed to withstand greater force than would be expected.

 

BEAMS and BRIDGES

The simplest way of supporting a load across a gap is to use a beam. This is the simplest form of bridge,  using a tree trunk to span a stream. What is actually happening is that the forces that act upon the beam or bridge, caused by any load upon it and the weight of the beam itself, are being transferred to the support either side, as in Figure on the left.

If the beam has a force that acts in the middle  ( it could be its own weight ) , then the forces at either end are equal.  In this figure, we have that Force at Point x = Force at point y = 500 N

 

Together they are also equal to the total force acting downwards.

These are said to be equal and opposite reactions. If the force is moved  towards one end then that end needs to react more, and subsequently  the other end reacts less, but together they are always equal to the total downwards force.

What happen if the load is not in the centre?

Look at the  example shown in the next figure. The reactions at Y  ( red point ) will be  less than at X ( greenpoint ).

Activity:

a ) Draw in your notebook  this example and calculate the reaction in A and in B.

Don’t forget that Fx + Fy = 1000 N

b ) Try to find out the general formula for any exercise.

 

 

What happens in a beam?

When beams bend, the top surface is compressed and the bottom surface is stretched as  shows in Figure. You  can see, therefore, that the important areas for a beam to be strong are the top and bottom. The strength at the centre is not  so important.

In practice the major design issue with beam construction is making the  beam as light as possible without reducing its strength. This is called the ‘strength-to-weight ratio’.  The cross- sectional shapes of modern beams have enabled them to become lighter without compromising strength.  The next  figure shows a range of beam sections.

 

Structural Elements

In this illustration we have:

1º Foundation: Made of reinforced concrete that supports all the weight.

2º Columns: They transmit the building’s weight to the foundations

3º Primary beam and secondary beam are arranged to support the floor ( Blue area )

 

4º Arch.  Like a single beam bridge, the arch transfers the load to the Foundations.

Think that each structural element of an arch is either joined by screws or  welding. So, what about the roman arched bridge?

 

 

Have a look at the next image

 

 

 

In the keystone the top end is bigger than the bottom end so the stone never falls and the arc is formed.
The weight is shared by the lateral faces of the stones until it reaches the foundations.

Suspension bridge

 

A bridge is a structure built to span a  physical obstacle such as a river or two pieces of  land separated by the sea. The first bridges were simple wooden beams, but nowadays they are complicated structures.

A suspension bridge is a type of suspension structure.  There are  several beams which  are hold by dozens of steel wires.

they could have 2 or more Columns, which support all the weight. The space between two columns   is called Span.

This type of structure is very good for covering large distances ( large span ) but are very expensive.

 

 

Stability

 A stable structure is one that is safe and will not fail under the conditions for which it is designed.  Structures often gain stability from having a triangulated structure. There are many examples of triangulated structures such as house roofs, bicycle frames, electricity pylons or bridges.

Let’s see an example:

Apply a pushing force as shown, and observe what happens to the frame.

Can you think of anything that can be done to prevent the structure from deforming like this?

The next illustration shows the simple triangulated system.

 

 

Activity: Copy  these structures in your notebook. Which of these structures is stable and which is non-stable?. What can you do to make them rigid?.

  Go to Structure exercises 

 

1º ¿ Como se clasifican los lápices ?.2º Dibuja una escuadra y un cartabón de forma que el ángulo que forme sea 60 º3º Repite lo mismo para que forme 135 º
4º Realiza la planta, lazado y perfil de las figuras que aparecen en la página:
https://www.petervaldivia.com/ejercicios/diedrico/index.php
5º Dibuja un borrador de pizarra y añade las medidas aplicando las normas de acotación

6º Una pieza mide en plano 7 cm. Si la escala es 1:200, que medida tiene en la realidad

7º Un campo de fútbol tiene en plano 10 x 7 cm. Si la escala es 1:500, calcular la superficie del campo, en m².

8º Un Chip representado en plano, tiene una medida de 30 cm de largo. Que medida tiene en la realidad si la escala es 2000:1

9º Aplicaciones, propiedades, ejemplos y método de obtener los metales.

10º Que es una aleación y escribe algún ejemplo.

11º Dibuja un tronco de un árbol y señala las partes mas importantes. ¿ Que parte del tronco es mejor para fabricar tableros de madera?

12º Explica como se realiza el secado de los tablones de madera.

13º La madera de roble tiene una densidad de 820 kg/m³.

14º Que es una fundición, propiedades y para que se utilizan

15º Que características tiene el hierro dulce

16º Propiedades del cobre.

17º propiedades del aluminio. Aplicaciones

18º ¿Porque se añade estaño al bronce?.

¿Como mejoran sus propiedades ?

19º Explica brevemente el proceso de obtención del hierro

20º Dibuja una celda electrolítica y explica como se obtiene el aluminio

Questions about Materials

1º How can you turn the water back to ice?. Does ice take up a bigger or smaller volume than water?.

2º Optical properties. Definitions and examples.

3º What is a Biodegradable material?

4º What happens if you heat the steam bellow 100 ºC.

5º A Material that lets water through is called …………………

6º Fill the gap. A _______ is a waterproof material very strong that doesn’t allow light past through it and is not flexible.

7º Can you name a rock that floats on the water

8 Why is electrical wiring usually covered with a layer of plastic?
9º Draw the Top view, Side view and Front view of the next figure

10. What is a plywood. How is it made and properties

11º What is an artificial material. Examples

12º People have used wood for many purposes such as: ……..

13º Properties of Iron and wool.

14ºWhat would be a good rock to tile a roof with and why?

15º Define Ductility, Electrical and thermal conductivity and Malleability

16º Define Hardness and Density

17º Metallic bond

18º Classification of metals according to their density. Examples

19º What percentage of carbon is in steel. Properties and example of applications

20º Siderurgic processes. Fill up the gaps using these words:

– waste materials , chemical reaction, carbon , elements, Hot air, iron, molten, steel industry, carbon content, out of the bottom, of the bottom, into the bottom

________ is introduced into the lower part.
When the materials descend a __________ takes place. The ______ separates from the which were contained in the original mineral.
The _________ stay at the top and the______ metal comes __________ (iron +____ + impurities).
The molten metal is directed towards the ________ to adjust the _______.
21º What is a screwdriver?

22º What is a Files ?

23º Stamping Treatment.

24º Tin. It is a metal or a alloy?. Feature and applications.

25º  Cast iron and steel -> Production->The Blast Furnace.  Choose the correct words for each question

a) The mineral in which there is a mixture of  rock and iron oxide  and rock is called

a1 ->  Bauxite

a2 -> Ore

a3-> cast iron

a4 -> Stainless Steel

b) Hot air is introduced ……

b1) With the ore and the gangue

b2) into the high part

b3) To obtain the  no ferrous minerals

b4)  into the lower part.

c) The element which burns with air is

c1) -> Oxygen

c2) -> Iron

c3 ) -> Carbon

c4 ->  CaCO3

d) In the blast furnace the iron is separated from the oxygen, transforming the _______ into pure iron

d1) Iron oxide

d2-> Ore

d3) -> gangue

d4 -> iron mineral

26 ) Bronze is an ______ of about 90 % ______ and about 10% ______

27)  ____ is very resistant to corrosion and this property makes it suitable for coating other metals, such as cans.

28 )  ___ melts only at 232 ºC, so it is used for welding copper elements.

29 )  Complete the paragraph by choosing words from the list given. You can choose the same word several times.

The first metal to be used was ____. Some rocks with _____ minerals were probably next to a fire. The fire made the _____ melt and drip from mineral, forming a pool on the ground.
Later came ____. This probably was also found accidentally. Minerals containing _____ also often contain ___, so as both metals dripped from the minerals they mixed.
And finally _____. When we melt ______ using a wood fire, a bit of _____ mixes with the molten ____ and the result is _____.
In ancient times, miners found metals only in small amounts (especially silver and gold) so they were very valuable.

Words: Tin , Bronze,  Iron ( 3times ),  copper ( 4 times ), Carbon, Steel

Dictionary:

Drip: The formation and falling of drops of liquid. Example of expression  ->

“there’s a drip through the roof”

 A Bit about Temperature and heat.

Heat always travels from a warmer area to a cooler one. In a fridge, there is a heat-exchanging tube  ( Evaporator ) that absorb heat from the hoot food  and it is leaves  because another heat-exchanging tube ( Condenser )  outside   the refrigerator.

In Spain, Temperature is measured in degrees Celsius (°C). In  USA and  UK  is measured in degrees Farenheit (°F).  For example, in case of water:

Ice melts at  0°C.
Water boils at 100°C

Now, watch the next video and pay attention.

1º Click on  video 1

2º Click on  video 2

3º Click on  video 3

Activity: Copy in your notebook the questions of every video. Replay all the question after watching the videos

Exercises 1: Use as many words as you need to describe the following materials:

Properties: Strong, light, weak, heavy, low density, translucent, electrical conductor, magnetic

a) Wood   b) Plastic  c) Fabric  d) Iron   e ) Glass    f ) Cork   g) wool   h)   Aluminium

Exercise 2: Copy into  your notebook the properties of transparent, opaque, waterproof, hard, strong and conductor.

Rocks and soils

Rocks can be  permeable or impermeable hard or soft, or even can splits easily into thin sheets such as the Slate. We are going to learn some aspect about granite,  marble, chalk and slate.
Soils are a combination of very small  particles of rock, dead animals  and plants  plus  air and water.

4º Click on  video 4

 Exercises 3. Test Only read and Think.

1.Which of the following rocks is permeable?
A.  Granite
B.  Slate
C.  Marble
D.  Chalk
2.Which rock splits easily into thin sheets?
A.  Granite
B.  Slate
C.  Marble
D.  Chalk
3.Which is the only rock that floats?

A.  Pumice
B.  Slate
C.  Marble
D.  Granite
4. What would be a good rock to tile a roof with?

A.  Slate
B.  Marble
C.  Pumice
D.  Chalk

5. Granite is often used for steps because …
A.  it doesn’t wear away easily
B.  it is very nice
C.  it doesn’t float
D.  it’s permeable

6. Chalk is used to write on blackboards because …
A.  it doesn’t float
B.  it wears away easily
C.  it’s permeable

7.Marble is often used for statues or grand buildings because …

A.  It has attractive textures and colours
B. It splits easily into thin sheets
C. It is waterproof
D. It wears away easily

Now, go to Hot potatoes exercises

Conductors and Insulators. Try not to blow anything up!

5º Click on  video 5

Exercise 4: Test

1. An electrical conductor is
A. A material that lets electricity pass through it
B.  A material that does NOT let electricity pass through it.
C.  A raw material
D.  A material that lets heat pass through it

2. Which of the following materials is an electrical insulator?
A.   Copper
B.  Gold
C.  Cork
D.  Wet paper
3. Why is electrical wiring usually covered with a layer of plastic?
A.  To make it look very pretty
B.  To protect against water
C.  To help electricity flow quickly along the wire
D.  To make it safe for people
4. A electrical wiring is usually made from …
A.   Copper
B.  Silver
C.  Iron
D.  Steel
5. Mary makes a simple circuit with one bulb and three 1,5 volts batteries. The bulb lights for 2 seconds and then blow up. Why?
A.   Too much electrons flows through the filament
B.  The batteries are all flat
C.  Not enough electricity flows through the circuit
D.  The bulb’s filament is not hot enough

Now, go to Hot potatoes exercises

Dictionary:

Cork: The elastic outer bark of the holm  oak, used especially for insulation,  bottle closures, etc.

On the left, a holm oak, a typical tree in Extremadura

Pumice: A light, porous, glassy lava rock.

 There are two significant groups of metals:
Ferrous metals: contain iron. First figure ( boat )
Non-ferrous metals: do not contain iron. Example, copper tubes

To choose the correct material for any particular task is essential for a manufacturing activity.

Non-Ferrous metals:

Examples of Non-ferrous metals are: Aluminium,  copper, gold or silver

Plastic

Made using coal, gas, animal protein or petrol
On the left,  plastic bottles

Other Materials used in manufacturing activity are Ceramic, textiles and glass

 

Properties of Materials

Properties of materials can be divided into physical, chemical and ecological

Physical Properties

Electrical Conductivity: When electricity can run though the material.
Examples:
Steel is a good conductor
Wood isn’t a good conductor

Optical properties:

How materials behave when light touches them
Them can be classified into:
a) Opaque: No light travels through them. e.g wood
b) Transparent: All light travels through them and you can see what’s behind the materials. e.g glass of window
c) Translucent: All light can travel through them but you cannot see what’s behind them e.g frosted glass

Thermal Conductivity

 

¿ What is conductor and what is insulator ?

Plastic handles are …
Metal Body is …

Thermal conductivity is the ability of the material to conduct heat. e.g. Saucepan. Metal body for thermal conductivity and plastic handles for thermal insulation.
Thermal Insulation = It is a bad Thermal conductor

 Dilation and contraction and Fusibility

Dilation: When material expands ( gets bigger ) due to heat
Contraction:  When material gets smaller due to heat

To think about: Why are rails separated by a gap?

Fusibility is the ability of a material to change into a liquid when heated to its melting point.
Examples of melting points
Iron´s melting point………..1535 ºC
Copper´s melting point……….1083 ºC

Sound Properties

The ability of materials to conduct sound

To think about. Can you speak on the moon?

Write some examples of good and bad conductors

Chemical Properties

Oxidation: The change that occurs to most metals when in contact with air or/and water

Ecological Properties

Recyclable. Materials that can be reused
Toxic. Materials which are harmful to the environment
Biodegradable. Materials that decompose naturally with time. eg
An apple take about 20 days to decompose
Plastic takes about 100 years
Glass takes about 400 years

Choosing the correct material for any particular task is essential for a manufacturing activity.
Materials are divided into:
Raw materials ( natural and artificial ) and
Processed materials ( artificial materials )
Natural materials such as wood or stone exist in nature and we use them as they are. Example of these materials are wood, stone, sand, wool etc
Natural resources are split into 3 categories:

• Animal

• Vegetable

• Mineral

Artificial Materials

Artificial materials or Processed materials are those which have been transformed by man.
For example, iron is a natural material because we obtain it from mines. If we add carbon atoms to the iron, we get steel and steel is stronger that iron with better properties.
Even more, if we also add chrome, we get Stainless steel. It is also called corrosion-resistant steel
So stainless steel is an artificial material, although we get iron from nature ( natural material )

Wood

Divided into two major classifications:
Hardwoods and Softwoods
There is great confusion about the terms hardwood and softwood. These terms do not refer to its technical properties but its origin. In this way, there are softwood trees which have hard wood and viceversa.
Most Softwood trees have spiky leaves with branches forming rings
Hardwood Trees have broad, flat leaves. Branches usually grow at different levels and never more than two at the same level

Types of trees
Spiky leaves	broad-leaved

 Wood is an organic material. In a living tree it transfers water and nutrients to the leaves. It has a support function, enabling trees to reach large sizes or to stand up for themselves.
We also call materials engineered made from wood ‘wood’ , such as wood chips
People have used wood for many purposes such as:

Fuel

Construction material for making houses.
Weapons , paper, furniture, tools, etc.

In a tree trunk ( image on the left ) , not all the parts offer the same quality wood.

The best part are the sapwood and the heartwood.
The wood at the center of the trunk is called heartwood and it is older, darker and more durable than the surrouding wood.

As a tree grows, a thin layer of cells called the cambium generates new wood, called sapwood
Sapwood is softer and lighter in color than heartwood. As the sapwood ages, natural substances invade the sapwood and gradually convert it to heartwood.
Furniture made of hearwood will last longer than furniture made of Cambium wood

Wood can be dated by carbon dating and in some species by dendrochronology .

But dendrochronology is very useful to know about the year-to-year variation in tree-ring widths and gives clues to the climate at that time. Click on dendrochronology

Artificial wood planks

 It can defined as wood products manufactured by glueing together wood particles ( wood chips ) or fibres

Plywood is a type of composite wood made from thin sheets of wood. Alternative layers are glued together so they have their grain at right angles to each other for greater strength	Fiberboard Fibre boards is made of a mixture of glue and wood fibers. It much cheaper than natural wood because it is made from wood chips. Fibre board is heavily used in the furniture industry. For pieces that will be visible, a layer of wood is often glued onto fiberboard to give it the appearance of conventional wood ( See image above ).

Dictionary:

 

Wood chips  are used primarily as a raw material for technical wood processing.