StructuresHold, protect & provide shape

Manuel Ángel Martínez García (manuelmg@educastur.princast.es)Jesús Prieto Fuentes (jesuspf@educastur.princast.es)Víctor Manuel Sánchez Canga (victorsc@educastur.princast.es)Grupo de trabajo PALE 2008 – Área de Tecnología

Unit Layout (9 lessons) Structures (Technology - 2nd Year of ESO)

What are structures? Examples in Asturias. Different types of structures

Frame, Shell, Solid (or mass). Types of forces acting on structures

Compression, Tension, Bending, Torsion & Shearing. Structural elements

Beams, columns, joists, foundations, steel sections, arches, ...

Joints Rivets, welding, nuts & bolts, hinges, ...

Projects 3 projects ...

Summary

Aims and objectives

Aims To raise students’ awareness of the role played by

structures in common objects.

To show how structures work and how we can use them in our projects.

ObjectivesAt the end of the unit,

Most of the students should be able to identify different types of structure and explain their use.

Most of the students should be able to analyze simple structures and forces.

Some of the students should be able to design simple structures with certain constraints.

Vocabulary

Beam. Joist &Breeze Block

Steel Sections (T, I, …). Columns

Rivets Welding Nuts & Bolts Hinges

What are structures?

Everything has a structure.

A structure is something that 1. Protects.2. Provides shape.3. Supports loads.

What are these structures for?

Functions1. Protects.2. Provides shape.3. Supports loads.

31,2,3

1,2

Structures in Asturias I

Coal washing plant

Saints Bridge (Asturias- Galicia)

Fernández Casado Bridge (Asturias- León)

Cangas de Onís Bridge

Structures in Asturias II

Coal mine shaft

Grandas de Salime dam

Negrón Tunnel (Asturias- León)

Steel Factory cooling tower

Structures in Asturias IIIOviedo

Cathedral

Church in Universidad

Laboral

Viaduct,Luarca

Oviedo Congress Centre

(Calatrava)

Types of structures IMass Structures

Solid structures which rely on their own weight to resist loads. Examples: a brick, a dam.

Shell structures Made or assembled to make one piece, usually thin sheet material with ridges or curves to make it stronger. Examples: Tin cans, bottles, car and airplane bodies, …

Types of structures II

Frame Structures These are made from many small parts (called members) joined together. Bridges, cranes and parts of an oil rig are a few examples.

Structures can also be classified as

Natural StructuresMade by natural means

Manufactured StructuresMan-Made

Loads I

Loads can be either static or dynamic.

Static LoadsThose which remain constant.

Example: the weight of the materials from which a structure

is made.

Dynamic LoadsThose which exert constantly

changing forces upon a structure. Example: a car crossing a bridge.

Loads II

Loads produce the following effects.Bodies with Elastic Behaviour (elasticity)

They change their shape, but return to their original form when the load is removed. Most materials exhibit elastic behaviour to some

extent. For example: gently bend a plastic ruler.

Bodies with Plastic Behaviour (plasticity)They change their shape, but they don’t return to their original form when

the load is removed. For example: bend a paper clip. Up to a certain point, a paper clip will spring back into shape. If you bend it too far, it springs back

slightly but stays permanently bent. This means it has been bent beyond its elastic limit.

Loads III

Bodies with Rigid Behaviour (rigidity)They don’t change their shape when a load is applied. If the load is

too heavy, they just break.

REMEMBER

1. Structures should operate within the elastic limit of their materials.

2. Structures shouldn’t break under the weight of loads.

3. Structures shouldn’t change their shape significantly under the weight of loads.

Example: If you try to bend a piece of glass, you can’t. If you increase the force beyond a certain limit, the glass just breaks. It is said

that glass is rigid.

Loads IV

Types of Loads Loads are produced by forces. Depending on these forces, the following effects can be caused:

Compression - for example, the buckling of a bridge pier.     

Tension - for example, the stretching of a suspension bridge chain or strut                       

Bending - compression and extension combined, for example, with a bridge beam.

Loads V

Torsional or twisting of a bar or a key in the lock

Shear ,for example, a bridge beam, a metal shear or a cutting pliers 

Loads VI

Compression

Bending

Example

Structural analysis Determine the type of load affecting each piece of a structure 

Load

Idea Imagine a piece of the structure breaks. What happens to the pieces?

Load Load

Tension

Compression

Loads VII

Stability (I)

Structures should be stable They should support external loads without falling down, falling over or collapsing.

Unstable building

Unstable slope

Stability (II)

We can gain stability in our structures by:

a) Choosing an adequate shape flat and wide shapes are the most stable.

b) Lowering the centre of mass

Stability (III)

c) Anchoring the structure to the floor Using wires.

d) Sticking the structure into the floor Deep foundations

Structural Elements I

ArchesThey stop the downward bend of a flat beam. The forces in an arch are transferred to the foundations at the base of the arch. The weight is carried down along two curving paths.

How can we build strong structures?By using resistant structural elements made of light, resistant

materials.

BeamsThese are horizontal elements designed to support bending, produced by vertical forces.

Structural Elements II

Joists

• These are the horizontal supporting members that run from wall to wall, wall to beam, or beam to beam, to support a ceiling, a roof or a floor. They are made of wood, steel or concrete.

• They are often supported by beams and are usually repeated.

• Beams are bigger than joists.Joist

Beam

Hollow concrete blocks or breeze blocks, to fill

gaps between joists

Structural Elements III

ColumnsThese are vertical elements designed to support horizontal loads and transmit the forces to the ground.

Foundation elementsThese are elements designed to reinforce the ground so it can bear the vertical forces produced by the whole structure built upon it. For example footing elements.

N.B.Foundations prevent the soil collapsing under the weight of the structure. The weaker the soil, the stronger (and more expensive) the foundations.

Structural Elements IV

ProfilesResistance of structural elements depend on:• The materials used to build the elements.• The shape of the elements. Some shapes (profiles) are stronger than others.

I shaped steel profileL shaped steel profileU shaped steel profileSteel tube

Structural Elements V

TrianglesVery useful for structures

ApplicationIs it possible to build a structure that supports a book with a piece of card?

Structural Elements VI

SolutionFolding the piece of card forming arcs and triangles.

Evaluation

Learning: Activities Exam

Teaching: Pass rate of students Less than 60% Unsatisfactory From 60%-70% Poor From 71%-80% Acceptable From 81%-90% Good More than 91% Very good

Questions are welcome

Plenary

Bibliography & acknowledgements

In this work we have use pictures and taken information from the following sources:

The Internet, specially these sites

•http://en.wikibooks.org/wiki/SA_NC_Saaste_Tech:Modules_Structures_grade_5

•http://www.chester.ac.uk/~mwillard/sci_ed/structures/structures.htm

•http://www.edselect.com/grade51.htm

•http://www.deyes.sefton.sch.uk/Technology/Keystage3/structures.htm#WHAT%20IS%20A%20STRUCTURE?

•“Design & Technology”, by James Garratt (ISBN0-521-55607-4)