DESIGN & TECHNOLOGYUPPER SECONDARY

STRUCTURESSTRUCTURES

7051 syllabus-intro7051 syllabus-intro

Understand what a structure is.Understand the need for manufactured

structures.classify natural and man-made structures

as in plants, trees, honeycombs, webs, animal skeletons vs. that of bridges, cranes, pylons, roofs, domestic furniture

STRUCTURESSTRUCTURES

(1) They must resist forces(2) They must not collapse during use(3) They must hold parts in the right place

Structures are in all shapes and sizes; from a molecule tothe largest volcano. But they have 3 things in common :

Molecules Volcano

Definition of StructuresDefinition of Structures

Structures are things that are made or exist naturally to resist forces or loads.

STRUCTURES EVERYWHERESTRUCTURES EVERYWHEREStructures can be big and small

Show can

samples to

students

STRUCTURES EVERYWHERESTRUCTURES EVERYWHERECan you name these famous structures?

ANCIENT STRUCTURES ANCIENT STRUCTURES How were they build? Which country canyou find them?

MODERN STRUCTURES MODERN STRUCTURES

FUTURE STRUCTURES FUTURE STRUCTURES

QUIZ NO:1QUIZ NO:1The pictures earlier show mammoth future structures in mega projects. With the advance of technologies, the structures can be constructed. But do you think that structures in future will also become smaller and smaller?Discuss about a few structures that have shrunk over the years. (eg. Diskette to memory card)

STRUCTURESSTRUCTURES

NATURAL & NATURAL & MAN-MADE STRUCTURESMAN-MADE STRUCTURES

NATURAL STRUCTURESNATURAL STRUCTURESWhat about our skeleton ?

LeafAnt Hill

Spider Web Beaver’s Nest

There are also many structures found in nature. These natural structures have evolved over years due to the changes in the climate and the environment.

Show leaf samples

to students

MAN-MADE STRUCTURESMAN-MADE STRUCTURESThumb drive

Human Transporter

Bullet Train

Swimming pool

A structure that satisfy one or more of the functions of a structure and does not exist in nature will be classified as a man-made structure.

QUIZ NO:2QUIZ NO:2Where, in nature, do you think the designers of this structure get their ideas from?

QUIZ NO:3QUIZ NO:3Why does the swimming pool classified as a structure?

The walls of the swimming pool satisfy the conditions of a structure:1.Able to resist loads and forces of the water acting on its walls.2. Does not collapse when the pool is filled with water. 3. The walls stand erect.

STRUCTURES ACTIVITY 1STRUCTURES ACTIVITY 1Construction of a tall structure

Challenge :You are to construct a standing structure using the materials provided on the table. The structure is to be as tall as possible and able to stand firmly.

Discussion :How does each part of the structure support one another? Do the joints play an important role? Duration :10 mins

STRUCTURESSTRUCTURESFRAME & FRAME &

SHELL STRUCTURESSHELL STRUCTURES

FRAME & SHELL STRUCTURESFRAME & SHELL STRUCTURESMan-made Structures

Frame Structures Shell Structures

Members joined to formframes Outer shell provides strength

NATURAL FRAME STRUCTURESNATURAL FRAME STRUCTURESFrame Structures

Spider Web Skeleton Bird’s Nest

The frame provide support and strength.It provides protection to maintain its form.

MAN-MADE FRAME STRUCTURESMAN-MADE FRAME STRUCTURESFrame Structures

ScaffoldsStructural frame building Truss roof

A frame structure is constructed by joining separate pieces of materials, called members to support and protect various parts. The frame structure provides support and strength for the house.

MAN-MADE FRAME STRUCTURESMAN-MADE FRAME STRUCTURES

Before After

4 members are joined to form a simple frame structure.

Add a diagonal member toStrengthen the frame structure.

member members

Frame structures often consist of multiple pieces of members joining together to hold up the structures.

NATURAL SHELL STRUCTURESNATURAL SHELL STRUCTURESShell Structures

Terrapin shell Snail shell Egg shell Coconut shell

The hard shell provides support, strength andprotection.

SHELL STRUCTURESSHELL STRUCTURESShell Structures

The outer shell provides support and strength. They do not have a frame.

Safety helmetVacuum cleaner

Litter binsDrink can

QUIZ NO: 4QUIZ NO: 4

Does the computer external cover qualify as astructure?

Yes. -The external cover is the outer shell that provides support and strength. -It also protects the internal partsof the computer.

QUIZ NO:5QUIZ NO:5Designers look to nature for inspiration when creating today’s man-made structures. Where in nature, do you think the designers of this structure get their ideas from?

EGG TRAY

Honeycomb.

• Materials - sticks, grass, string, paper, and pine needles.

NATURAL VS MAN MADE NATURAL VS MAN MADE STRUCTURESSTRUCTURES

• Materials - bricksNatural Structures Man-Made Structures

• Bonding agent - Materials are bonded with mud, sticky saliva, tent caterpillar silk and spider webs.

• Bonding agent - Materials are bonded with mixture of sand and cement

FUNCTIONS OF FUNCTIONS OF STRUCTURESSTRUCTURES

FUNCTION OF FUNCTION OF STRUCTURESSTRUCTURES

1. SPANNING - BRIDGES1. SPANNING - BRIDGES

Beam Bridge

Truss Bridge

Arch Bridge

Suspension Bridge Cable-stayed Bridge

FUNCTION OF FUNCTION OF STRUCTURESSTRUCTURES

2. SUPPORTING2. SUPPORTING

FUNCTION OF FUNCTION OF STRUCTURESSTRUCTURES

3. PROTECTING3. PROTECTING

FUNCTION OF FUNCTION OF STRUCTURESSTRUCTURES

4. CONTAINING4. CONTAINING

Construct and test a Bridge usingcomputer modeling; West Point Bridge

Designer.

STRUCTURES ACTIVITY 2STRUCTURES ACTIVITY 2

Procedure :Download the West Point Bridge Designer programme from http://bridgecontest.usma.edu/download.htm. Construct a truss bridge and test the bridge using the computer model.Discussion :Identify which cross-section of the truss members will make the strongest bridge. How do you compromise between cost and strength?Duration : 15 mins

7051 syllabus-Forces7051 syllabus-Forces

Explain the terms ◦Loads◦Forces (tension, compression, bending, shear

and torsion)◦Struts◦Ties◦Beams & cantilever beam◦Describe their relation to structures

LOADS AND FORCESLOADS AND FORCES

FORCESFORCES2 types of forces acting on a structure

External forces Internal forces

External forces on the structure.

Internal forces act within thestructure.

FORCESFORCES

Rare Earth Magnets

Tower crane-strong enough to support weight and the containers

Tops of skyscrapers can sway due to strong winds blowing against them

High pressure steam in power station provide force to drive the turbines.

TYPE OF LOADSTYPE OF LOADS

Static Loads Dynamic LoadsLoads that are stationary & has constant size, position and direction on or within a structure.

Loads that are in motion & changes in size, position or direction.

LoadsLoads

QUIZ NO:6QUIZ NO:6The term forces also known as loads and vice versa. But what’s the difference between forces and loads?

Forces are external forces applied to a structure.Loads are forces due to gravitational pull or weight applied on a structure vertically through the centre of gravity of the structure.

QUIZ NO:7QUIZ NO:7

Bridges are subjected to dynamic loads most of the times as vehicles continuously cross over it. How do engineers prevent the bridge from collapsing due to the dynamic loads?

Both ends of the bridge or one end will be supported on rollers. The rollers will be ableslide and will not cause a structural damageAt the ends.

FORCES & LOADSFORCES & LOADSSI UNITS OF FORCE NEWTONS (N)Force = Mass (m) x Gravitational pull (g)

Where Mass (m) in kgGravitational pull in 9.81 m/s2 (or 10 m/s2)

Example: Amount of force produced by 1 kg of weight on a table

= 1kg (mass) x 10 (g)= 10N

1,000 N = 1kN (kilonewton)1,000,000 N = 1MN (meganewton)1,000,000,000N = 1 GN (giganewton)

TYPE OF FORCESTYPE OF FORCES1. Compression

member

In compression, the member of a structure (eg: leg of a table or truss in a bridge) will experience forces pushing towards its centre from two or more directions. Forces that cause compression are called compressive forces.

A member experiencing compression is known as a strut.

Compression – part of the structure is squashed.

TYPE OF FORCESTYPE OF FORCES2. Tension

member

In tension, the member will experience forces pulling away from its centre from two or more directions. Another word for tension is stretched. Forces that cause tension are called tensile forces.

A member experiencing tension is known as a tie.

TYPE OF FORCESTYPE OF FORCES3. Torsion

member

An member in torsion will experience a ‘twisting’ effect from the torsional forces. A force that causes torsion in a structure is called torque.

Torsion- part of the structure ‘twists

TYPES OF FORCESTYPES OF FORCES

Forces that causes a member of a structure to try to slide past another part are called shear forces.

member

4. Shear

TYPE OF FORCESTYPE OF FORCES5. Bending

member

A member in bending often experience compressive forces on one surface and tensile forces on the opposite surface. In the case above, the member would experience compression on the top surface and tension at the bottom surface.

STRUCTURES ACTIVITY 3STRUCTURES ACTIVITY 3Video presentation on forces.

Procedure :Make a 2 mins video presentation explaining the FIVE forces acting on a structure. Use your mobile phone camera to record your presentation.Use your creativity and innovation to present your findings. Discussion :Do you think that a structure will experience only one type of force or a combination of other forces? Provide examples. Duration :15 mins

QUIZ NO:9QUIZ NO:9

A concrete beam is strong in compression but weak in tension. When a concrete beam is subjected to bending forces, the lower part in tension will crack. How do engineer’s strengthen it?

Engineer’s add steel bars inside thebeam at the tension area that isat the bottom layer.

CANTILEVER BEAMCANTILEVER BEAM

Warehouse Storage Shelves

Cantilever

A cantilever is a beam that is supported only on one end. It isn't the strongest structure but is used as a structural element when the designer does not want to see a support under an object.

Study the diagram of a computer desk. Each member of the structure is under some type of force.

PART A: Is in tension because the weight of the computer is stretching it.

PART B: Is under compression because the weight of the computer unit and the members above that make up the desk, are pushing downwards and compressing it.

PART C and D: This is the same member but on the inside compression is taking place and on the outside it is being stretched (under tension).

QUIZ NO:10QUIZ NO:10

7051 syllabus-equilibrium7051 syllabus-equilibrium

apply the concept of equilibrium as a result of applied load and reaction

STRUCTURES IN STRUCTURES IN EQUILIBRIUMEQUILIBRIUM

EQUILIBRIUMEQUILIBRIUM

There are forces balancing the structures

EQUILIBRIUMEQUILIBRIUMWhy the objects do not fall?

The forces acting downwards is/are equal to forcesacting upwards.

EQUILIBRIUMEQUILIBRIUM

If several forces are applied to an object and the object remains stationary, or if the object continues to move with uniform velocity, the forces are said to be in equilibrium. Forces in equilibrium add to produce a resultant of zero.

400 N

200 N 200 N

10 N

10 N5 N

5 N

  Equilibrium Means "Zero Acceleration"

VECTORSVECTORSA force can be represented in a line diagram calleda VECTOR.

Vector diagram Each length of the line, drawn to scale, represents the size of the force The arrow head and angle of each line represents the direction of the force

SCALE : 20 N to 1 cm

F1 = 20 N

1 cmF2 = 40 N

2 cm

F1 + F2 = 60 N

3 cm

VECTORSVECTORSParallelogram of ForcesForce A = 60 NDirection of force is 45 0 to force BForce B = 40 NDirection of force is horizontal

Scale:200 N to 1 cm

Find resultant force.

40 N (2 cm)

60 N (3 cm)

45 0

4.7 cm

Resultant force = 4.7 x 20= 94 N

VECTORSVECTORS

The triangle of vectors addition method is :

1. Draw 40 N to scale and in the direction of its action.

Triangle of Forces

40 N (2 cm)

60 N (3 cm)

45 0

Scale:200 N to 1 cm

4.7 cm

Resultant force = 4.7 x 20= 94 N

2. From the nose of the 400 N force vector draw 600 N force vector using the same scale and in the direction of its action.

3. The resulting vector is represented in both magnitude and direction by the vector drawn from the tail of 40 N vector force to the nose of 60 N vector force.

MOMENTSMOMENTS

State of EquilibriumAnti-Clockwise moments = Clockwise moments

(Rotational Balance)

MOMENTSMOMENTS Moment = force x perpendicular distance

A 1000N load, at a distance of 15m from the fulcrum causes a moment of 15000 Nm. The further the distance between the load and the fulcrum, the greater is the turning effect.

To stop the crane from toppling over, a counterbalance is used on the counterjib on the other side of the fulcrum.

QUIZ NO:10QUIZ NO:10

A 2m long shelf weighing 20N supports a speaker weighing 40N placed 0.5m from the left hand edge. Find the reactions at the supports.

Solution to Quiz no:10Solution to Quiz no:10Weight of the shelf is acting at its centre.Let reaction force at right support be Rr

Assuming moments at left support= 0Rr x 2 = 40 x 0.5 + 20 x 1.0Rr = 20N

Therefore the Reaction force on the right support is 20N.

Since total downward force is 60N, the Reaction force on the left support is 60N-20N = 40N

7051 syllabus- reinforcing7051 syllabus- reinforcing

use different methods of reinforcing such as ◦Gussets◦Ribs◦Braces◦Laminating◦Honeycomb◦triangulation

REINFORCING STRUCTURESREINFORCING STRUCTURES

RIGIDITY

Gusset platesStiffened fold

Lamination Honeycomb

Ribs

Braces

MATERIALS

REINFORCING STRUCTURESREINFORCING STRUCTURES1. Rigidity• triangle is one of the strongest shapes• provide strength & rigidity•Unlike a circle or rectangle, it will not distort easily

TRIANGLES

REINFORCING STRUCTURESREINFORCING STRUCTURES1. Rigidity-Frameworks• TRUSS – triangular parts to provide strength and rigidity. Examples: Supporting roofs & Bridges

Frameworks made of triangular parts are called triangulated frameworks. Example: Geodesic dome

ACTIVITY NO: 4ACTIVITY NO: 4Activity

Build 4 types of polygons as shown and test the rigidity of each shape. While all of the other polygons can be bent into many different forms that are NOT regular polygons (with many different angles in each polygon), the triangle always keeps the same shape. It is the strongest polygon. Why is that?

ACTIVITY NO:4 SOLUTIONACTIVITY NO:4 SOLUTIONThe reason is because in all of the other polygons, all of the angles can change. There is nothing to stop them. However in the triangle, the angles can not change once the triangle is built. The angles are fixed. This is because a triangle has three sides and three angles, and each angle is fixed by the side opposite to it. If you look at the following picture, you can see that there is only one angle where the two free sides can connect to the third side, and that once connected, all of the angles are fixed

2. Stiffened FoldsA material can be stiffened by folding.

Because of the fold,the can is able to withstand70 kg of mass.

REINFORCING STRUCTURESREINFORCING STRUCTURES

REINFORCING STRUCTURESREINFORCING STRUCTURES3. LaminationThin sheet materials (are generally weak) can be strengthened by laminating several sheets together.

Layers of laminateLaminated sheets of wood were used to stiffen the back rest of a seat and a table top.

REINFORCING STRUCTURESREINFORCING STRUCTURES4. Honeycomb• Light but strong when under compression• Used in cavities of doors- sides of door apart and keeps the weight of the door to a minimum.

Top left corner of a honeycomb door

REINFORCING STRUCTURESREINFORCING STRUCTURES5. Gusset PlatesUsed to add strength to a joint

GussetPlates

They help to distribute the stress of the joint more evenly by increasing the area of the joint.

REINFORCING STRUCTURESREINFORCING STRUCTURES6. RibsUsed to add strength to a wall of a structure

Ribs

They help to stop the walls from caving in. They allows objects to be light but strong.

REINFORCING STRUCTURESREINFORCING STRUCTURES7. BracesAdd strength to a joint especially in bracketsand cantilevers

Braces

STRUCTURAL FAILURESTRUCTURAL FAILURE**HIGHER THINKING ORDER

Many factors contributed to a structural failure:•Poor selection/wrong use of material.•Lack of understanding of the forces involved in design.•Failure of a joint.•Fatigue resulting from changes in the properties of a material over time.•Excessive loads, more than the design load.•Incomplete knowledge of the conditions a structure is likely to face.

MODELLING MATERIALSMODELLING MATERIALS1. BALSAVery light hardwood that is easy to cut and shape.

2. PLASTICS SECTIONS & TUBINGSIdeal for modelling hi-tech furniture. Available in range of colours and sizes.

MODELLING MATERIALSMODELLING MATERIALS3. ARTSTRAWSLight and can be painted

4. Corrugated plastic sheets (Corriflute)Good for modelling shell structures

MODELLING MATERIALSMODELLING MATERIALS5. FOAMBOARDLight, rigid material made from a sheet of foam sandwiched between two sheets of card.

6. RIPSTOP NYLONFlexible, tear resistant plastic sheet

JOINING OF MATERIALSJOINING OF MATERIALS1. SCREWS AND NUTS2. PLASTICS RIVETS3. SPLIT PINS

4. HOT GLUE (semi-permanent joint)

JOINING OF MATERIALSJOINING OF MATERIALS5. DOUBLE SIDED TAPES6. EYELETS / POP RIVETS7. SPOT WELDING

End of structures moduleEnd of structures module