Post on 28-Jan-2015
description
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)