Vigyan Ashram, Pabal

Wind (N) Weight (N)

Why are bar forces important?

Buckling

Snapping

Tension and CompressionAre beams stronger when loaded in the middle or at the ends?

tensioncompression bending

Tension and CompressionBeam Bridge Truss Bridge

Cable Stayed BridgeArch Bridge

tension

tension

compression

compression

compression

bending

Tension and CompressionReinforced Concrete Beams

compression

tension

Strong and Weak ShapesSquare

Triangle

mechanism

Strong and Weak ShapesCylinder

Dome

Forces in a Roof Truss

Total weight of building (N) =

Wind Force On Roof (N) =

17,8000 N

3,4000N

8,9000 N 8,9000 N

34,000N

1) Will the building take off?

YES!

What about the forces in your design?Will your design take off?

Wind (N)

Weight (N)

Wind (N)

Weight (N)

Wind (N)

Weight (N)

Forces in a Roof Truss

Total weight on trusses (N) = 11,000 N

Wind Force On Roof (N) = 17,8000 N

8,9000N8,9000 N

34,000N

2) What is the maximum possible load on 1 truss?

Total Force on Roof (N) = 189000 N

Force on 1 Truss (N) = 63,000 N

What about the forces in your design?Start with the force on the pink members

What about the forces in your design?

What is the maximum possible load on the pink structures?

Wind (N)Wind (N)

Wind (N) Wind (N)

Weight (N)

Weight (N)

Weight (N)

Weight (N) Weight (N)

What about the forces in your design?Work out the total downwards load for your

structureCart – You have 2 trusses. Work out the load

on 1 trussUmbrella – you have 3 supports. Work out

the load on 1 support.

Forces in a Roof TrussLook at the overall forces on the object

63,000N

31500N 31500N

=

What about the forces in your design?

Draw your structure to scale on square paper 1square represents how many centimetres?

Draw your forces to scale onto your structure 1 square represents how many Newtons?

What about the forces in your design?

6.5cm = 13,000 N

6,500 N 6,500 N

8000 N

4000 N 4000 N

12,500 N 12,500 N

25,000 N10cm = 1m

6cm = 0.6m

1 cm = 0.1 m1 cm = 2000N

1 cm = 2000N1 cm = 0.1 m

2 cm = 0.5 m

1 cm = 10,000N

1cm

6cm = 1.5m

How big are these forces?Look at 1 joint (starting at supports)

tension

compression

31500N

31500N

31500N 31500N

44,500N

63,000N

31500N 31500N

What about the forces in your design?Look at each joint in turnWhat forces act on each joint?

Tension

Compression Compression

Tension

6,500 N

6,500 N

8000 N

12,500 N

8000 N

12,500 N

How big are these forces?Look at 1 joint (starting at supports)

tension

compression

31500N

31500N

31500N31500N

44500N

63,000N

31500N 31500N

What about the forces in your design?

Tension Compression

TensionTension

Tension

6,500 N

6,500 NCompression

4000 N 4000 N

4000 N

25,000 N

25,000 N

How big are these forces?Look at 1 joint (starting at supports)

63,000N

31500N 31500N

63,000N

44500N44500N

What about the forces in your design?

13,000 N

12,500 N

13,000 N

12,500 N

How big are these forces?

Look at the forces in the members of your structure

Tension = 31500N

Compression = 44500N

Compression = 44500N

Challenge!Use what you have just learnt to make this bridge trussBridges are made out of straws (compression), string (tension) and pinsCheapest bridge wins!

5 rupees per metre

5 rupees per straw

1 rupee per pin

12cm

What about the forces in your design?What about the purple bits?

Wind (N) Weight (N)Wind (N) Weight (N)

Wind (N) Weight (N)