StructureStructure

Let us go on a Let us go on a Learning JourneyLearning Journey

What is structure?What is structure?

Structure resists and withstands Structure resists and withstands forces, it does not collapse during forces, it does not collapse during use and holds parts at the right placeuse and holds parts at the right place

A structure spans, supports, contains A structure spans, supports, contains and protects and protects

What are the 4 functions of What are the 4 functions of structures?structures?

1.1. spanning between two pointsspanning between two points

2.2. Supporting a loadSupporting a load

3.3. Containing thingsContaining things

4.4. Protecting thingsProtecting things

What are some natural structures?What are some natural structures?

1.1. Leaf with mid ribLeaf with mid rib

2.2. Tree with branchesTree with branches

3.3. Animal skeletonAnimal skeleton

4.4. Bee hive with honeycomb cellBee hive with honeycomb cell

5.5. Human/ Animal skinHuman/ Animal skin

What are some man-made structures?What are some man-made structures?

1.1. Buildings with columns and floorsBuildings with columns and floors

2.2. Window frameWindow frame

3.3. BridgeBridge

4.4. ChairChair

5.5. ShelvingShelving

What are What are shellshell structures? structures?

Shell structure has Shell structure has a skin to provide a skin to provide their strength.their strength.

What are some What are some naturalnatural shellshell structures?structures?

1.1. Tortoise shellTortoise shell

2.2. Egg shellEgg shell

3.3. Animal/ Human skullAnimal/ Human skull

4.4. Animal/ Human skinAnimal/ Human skin

5.5. Coconut husk/ Seed podCoconut husk/ Seed pod

What are some What are some man-mademan-made shellshell structures?structures?

1.1. Safety helmetSafety helmet

2.2. Bin with coverBin with cover

3.3. Vacuum cleaner casingVacuum cleaner casing

4.4. Light bulb (glass)Light bulb (glass)

5.5. Blister Pack for batteriesBlister Pack for batteries

What are some What are some natural natural frameframe structures?structures?

1.1. Tree branchesTree branches2.2. Rib cage (human & animal)Rib cage (human & animal)3.3. Leg bonesLeg bones4.4. Skeleton (human & animal)Skeleton (human & animal)

What are some What are some man-made man-made frameframe structures?structures?

1.1. Bridges Bridges

2.2. Window grilleWindow grille

3.3. Bus shelterBus shelter

4.4. Umbrella frameUmbrella frame

5.5. Chair with 4 legs/ Stool with foldable legsChair with 4 legs/ Stool with foldable legs

Can you identify some structures in Can you identify some structures in the picture?the picture?

• Framework for roof• Scaffold for construction• Bridge• Bus body• Bus Shelter• Bus Stand and Signage• Building• Human Body• Tree branches• Leaves

What are some common types of What are some common types of bridges?bridges?

Beam bridgeBeam bridge Arch bridgeArch bridge Suspension bridgeSuspension bridge Cable-stayed bridgeCable-stayed bridge

What are What are some common causessome common causes of of structural failure? structural failure?

11. Due to natural disasters:. Due to natural disasters: earthquake, typhoon, hurricane, floods etcearthquake, typhoon, hurricane, floods etc2. Due to human errors:2. Due to human errors: Poor selection and wrong use of materialPoor selection and wrong use of material Failure of a joint(s)Failure of a joint(s) Incomplete knowledge of the conditions of a Incomplete knowledge of the conditions of a

structure likely to facestructure likely to face Wrong calculation of forces (failure due to external Wrong calculation of forces (failure due to external

force such as twisting force)force such as twisting force) Overload of forces on the floors of building or roof Overload of forces on the floors of building or roof

toptop Insufficient reinforcement (re-bar) used in making Insufficient reinforcement (re-bar) used in making

the columns of the building the columns of the building

Why are corrugated cardboard boxes used to Why are corrugated cardboard boxes used to contain electronic products?contain electronic products?

1.1. It absorbs shock from impact.It absorbs shock from impact.

2.2. It protects the product from been It protects the product from been damaged.damaged.

What are some packaging used in containing What are some packaging used in containing fast food and electronic products?fast food and electronic products?

1.1. Card or plastics folded to form Card or plastics folded to form containers.containers.

2.2. Small blister pack with thin transparent Small blister pack with thin transparent plastic over a thin card.plastic over a thin card.

What are loads and forces?What are loads and forces?

Structures are designed to withstand Structures are designed to withstand different types of forces such as:different types of forces such as:• External forces or load that act on the External forces or load that act on the

structurestructure• Internal forces that act within the Internal forces that act within the

structurestructure

What is static load?What is static load?1.1. A force that has A force that has

constant size, position constant size, position and direction on a and direction on a structure.structure.

2.2. Example:Example:1.1. Static load such as Static load such as

a picture frame a picture frame resting (stationary) resting (stationary) on a table top with on a table top with no change in forcesno change in forces

2.2. A fan attached to A fan attached to the ceiling that is the ceiling that is not switched on not switched on has forces that are has forces that are in constant position in constant position and direction.and direction.

What is dynamic load?What is dynamic load?

1.1. A force on a structure A force on a structure that changes size, that changes size, position or direction.position or direction.

2.2. Example:Example:

a. A child playing on a a. A child playing on a swing with changes in swing with changes in forces (dynamic/ forces (dynamic/ moving) and position.moving) and position.

b. A rotating fan with b. A rotating fan with changes in force and changes in force and direction.direction.

Why are the framework used to support the top of Why are the framework used to support the top of the building made of hollow tubes and are usually the building made of hollow tubes and are usually

smaller than those at the ground level?smaller than those at the ground level?

1.1. Hollow and smaller Hollow and smaller framework are framework are lighter load to be lighter load to be carried by columns/ carried by columns/ pillars at the ground pillars at the ground floor.floor.

2.2. It will not collapse It will not collapse easilyeasily

Name and sketch 5 types of forces acting on structures

compression tension bending

torsion shear

Draw to show the effects of forces on Draw to show the effects of forces on structures (1) structures (1)

(a) Compression(a) Compression member: Strutmember: Strut

• Pressing forcePressing force• Squashing forceSquashing force

(b) Tension(b) Tension member: Tiemember: Tie

• Pulling forcePulling force

(c) Bending(c) Bending member: Supported Beammember: Supported Beam

• Bending force Bending force

(a) (b)

(c)

(d) Torsion(d) Torsion member: beammember: beam

• Turning/ Twisting force Turning/ Twisting force

(e) Shear(e) Shear member: Shackled pinmember: Shackled pin• Cutting forceCutting force

(d)

(e)

Draw to show the effects of forces on Draw to show the effects of forces on structures (2) structures (2)

Copy and complete the table on forces shown below

Example Type of force

Effects of force

Turning a screw

Torsion twisting

Bending a beam

Bending force bending

Pulling on a cable

Tensile force Pulling

What does equilibrium mean in What does equilibrium mean in structure?structure?

Both action and its reaction are equalBoth action and its reaction are equal Forces are in balancedForces are in balanced

What is moment?What is moment? It is the turning effect of It is the turning effect of

the product of load and the product of load and the perpendicular the perpendicular distance from the distance from the fulcrum or pivotfulcrum or pivot

Moment = Force x Moment = Force x Perpendicular distance Perpendicular distance from fulcrumfrom fulcrum

D

F

Moment = Force x DistanceMoment = Force x Distance

D

F MomentMoment

= F (N) x D (m)= F (N) x D (m)

(Nm)(Nm)

If F=100N; D=10mIf F=100N; D=10m

Moment= 100N x 10mMoment= 100N x 10m

= 1000 Nm= 1000 Nm

Uses of Moment in Everyday LifeUses of Moment in Everyday Life Example 1Example 1 - - Measurement Balance used in the Measurement Balance used in the

Chinese Medical ShopChinese Medical Shop

In equilibrium

Clockwise Moment (CM)=Anti-Clockwise Moment

(ACM)

FbFa

xa xb

Fb . xb = Fa . xa

Principle of Moment and EquationPrinciple of Moment and Equation

Experiment to Demonstrate MomentExperiment to Demonstrate Moment

By changing the By changing the weight, Wweight, W1 1 and keep and keep

WW22 at 30g; take down at 30g; take down

in the table the in the table the corresponding corresponding distances from the distances from the weights to the pivot weights to the pivot for the ruler to for the ruler to balance. balance.

W1 W2

X1X2

You may want to try this with simple apparatus using rulers etc

Example – Tower Crane in Construction SiteExample – Tower Crane in Construction Site

Uses of Moment in Everyday LifeUses of Moment in Everyday Life

Counterweight/Act as a counterbalance

What is a counterweight used for?What is a counterweight used for?

To check forces/ moments are balancedTo check forces/ moments are balanced To balance loads on both endsTo balance loads on both ends

Counterweight

Load (kg)=50kgLoad (kg)=50kgForce (N) =50 x gForce (N) =50 x g =500N=500NTake moment at R1Take moment at R1CM=ACMCM=ACML x 5=R2 x 10L x 5=R2 x 10500N x 5m=R2 x 10m500N x 5m=R2 x 10m2500Nm=10 x R22500Nm=10 x R2R1=R2=250NmR1=R2=250Nm

A simple supported beam weighs A simple supported beam weighs 50kg rests on two edges.50kg rests on two edges.

Calculate its reactions at R1 and R2.

5m

10m

R1 R2

L

Force (N) =500kNForce (N) =500kNTake moment at R1Take moment at R1CM=ACMCM=ACMF x 3=R2 x 10F x 3=R2 x 10500kN x 3m=R2 x 10m500kN x 3m=R2 x 10m1500kNm=10 x R21500kNm=10 x R2R2=1500/10 kNmR2=1500/10 kNm =150 kNm=150 kNmR1=500-150 kNmR1=500-150 kNm =350 kNm=350 kNm

A force of 500kN is acting on a beam A force of 500kN is acting on a beam that rests on two edges at R1 and R2.that rests on two edges at R1 and R2.Calculate its reactions at R1 and R2.

3m

10m

R1 R2

F

Tower crane lifting a loadTower crane lifting a load

Name the type of structure found in the tower crane.Name the type of structure found in the tower crane. Framework structureFramework structure

Explain the benefits of the triangular forms used.Explain the benefits of the triangular forms used. It is the strongest shape in structure designIt is the strongest shape in structure design Does not distort easilyDoes not distort easily It provides strength and rigidityIt provides strength and rigidity

The load causes a turning moment on the tower The load causes a turning moment on the tower crane. Explain the term “Moment”.crane. Explain the term “Moment”.

It is the turning effect produced by a force on the It is the turning effect produced by a force on the tower about a pivot (fulcrum)tower about a pivot (fulcrum)

What is What is elasticityelasticity??

•The The elasticityelasticity of a material is its ability to of a material is its ability to return to its original shape after being return to its original shape after being deformed.deformed.

•When a material does not return to its When a material does not return to its original shape after being deformed, it is original shape after being deformed, it is said to be ‘plastic’.said to be ‘plastic’.

What is stress?What is stress?

1.1. Stress is a measure of the force acting on a Stress is a measure of the force acting on a unit of a materialunit of a material

2.2. Stress = force / AreaStress = force / Area3.3. Unit of measure is kN/m Unit of measure is kN/m

Stress () = Force/ Area

What is strain?What is strain?

1.1. Strain is the amount of extension per Strain is the amount of extension per unit length in a material that has been unit length in a material that has been stretched.stretched.

2.2. Strain = extension / Original Length.Strain = extension / Original Length.

Draw a development of a drink packet Draw a development of a drink packet made from a single sheet of materialmade from a single sheet of material

How is it made?

The development is one that is made from a single folded sheet of material held together either using tabs and slots, or with glue

Structures often need reinforcementStructures often need reinforcement

Explain the need for reinforcement.Explain the need for reinforcement. To provide rigidity and stability for To provide rigidity and stability for

framework such as truss (use to framework such as truss (use to support roofs and bridges) support roofs and bridges)

Triangles do not distort in shape Triangles do not distort in shape under loadsunder loads

Why are triangles considered one of Why are triangles considered one of the strongest in structural design?the strongest in structural design?

1.1. Framework that includes triangles Framework that includes triangles provide strength and rigidityprovide strength and rigidity

(Unstable structure)

(Rigid and Strong)

What are the methods to make a What are the methods to make a structure rigid structure rigid ??

StructureStructure MethodMethod

Shelving System (Wood)Shelving System (Wood) HardboardHardboard

Shelving System (Metal)Shelving System (Metal) Triangular bracesTriangular braces

Thin sheet metalThin sheet metal Folded edgesFolded edges

A sheet of paperA sheet of paper Rolling/ FoldingRolling/ Folding

Few sheets of veneerFew sheets of veneer LaminationLamination

Right angle jointRight angle joint Gusset platesGusset plates

Bus stop shelter/ roofingBus stop shelter/ roofing RibRib

Wall bracketsWall brackets BracesBraces

Examples of methods to make a Examples of methods to make a structure rigid structure rigid ??

TypeType MethodMethod

Thin sheet metalThin sheet metal Folded edgesFolded edges

A sheet of paperA sheet of paper Rolling/ FoldingRolling/ Folding

Egg CasingEgg Casing Ribs/ Folded edgesRibs/ Folded edges

What are the methods to make a What are the methods to make a structure rigid structure rigid ??

Few sheets of veneerFew sheets of veneer

e.g: Plywoode.g: PlywoodLaminationLamination

Right angle jointRight angle joint Gusset platesGusset plates

Roof of Bus stop shelterRoof of Bus stop shelter RibsRibs

Wall bracketsWall brackets BracesBraces

Gusset plate

The figure shows a piece of The figure shows a piece of packaging.packaging.

Name 2 features Name 2 features that reinforced that reinforced the packaging:the packaging:

RibsRibs Safety folded Safety folded

edgesedges

What are the stiffest cross-What are the stiffest cross-sectional shapes under bending? sectional shapes under bending?

most stiff

least stiff

Tightly rolled paper tubes are used Tightly rolled paper tubes are used to model a structural designto model a structural design

What are the different What are the different methods of joining/ methods of joining/ holding the ends of holding the ends of the tubes together the tubes together in a tetrahedron in a tetrahedron shape?shape?

Preformed end capPreformed end cap Punched hole with Punched hole with

eyeleteyelet Gusset platesGusset plates Inserting wiresInserting wires

How is a geodesic dome shape How is a geodesic dome shape like?like?

•Frameworks made of triangular parts are called triangulated frameworks.

•A geodesic dome has a triangulated framework.