pwr pt science bridge gap materials
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The Final Test
Before the opening ceremony in 1859, theVictoria Bridge underwent a safety test.
The test consisted of an 18 platform cart train filledto capacity with rocks crossed the bridge. The
train and load weighed about 1 ton/foot.
The two locomotives hired to pull the train across
were insufficient and a third was required.
In spite, of all this weight, the deflection (bending)
of the bridge was a little over 1 inch and returned
to normal as the load was removed.
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The Victoria BridgeA quick overview of the Tubular design
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Situation
The Victoria Bridge was a technological
marvel, yet the engineers in chargeknew less about materials than we do
today.
Justify which material you would have
chosen for the project.
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What to consider?
What should one consider before
selecting the construction materials?
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What to consider?
What are the stresses/external forces thematerial will undergo? (Constraints)
How do we want the material to react to suchstresses? (Deformation)
How will the material react? (Material
properties)
Will the material last a long time?(Degradation)
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Constraints
What external forces are at play?
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Constraints
A constraint is the effect external forces
have on a material/object/system.
Examples of constraints:
Pulling an elastic band
Squishing a sponge
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Types of Constraints
There are 5 main types of constraints
Compression
Tension Torsion
Deflection
Shearing
Using the definitions soon to be provided, can you give a
common everyday example for each of these constraints?
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Types of constraints
Compression:
When a material is subjected to forces that
tend to crush it
Tension
When a material is subjected to forces that
tend to stretch it
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Types of Constraints
Which constraints would a bridge most likely
be subjected? Explain your reasoning.
5 Constraint reminder:
Compression
Tension
Torsion
Shearing
Deflection
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Deformation
Ways that materials react to the
constraint
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Deformations
A material deformation is the change in
shape of a material based on the constraints
that are applied.
There are three main types of deformations
Elastic
Plastic Fracture
Using the definition soon to be provided, can you give a
common everyday example for each of these
deformations?
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Types of material deformation
Elastic:
When the constraint leads to a temporarychange in the shape or dimensions of thematerial.
When the constraint is removed, thematerial returns to its original form.
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Types of material deformation
Plastic:
The constraint leads to a permanent
change in the shape or dimensions of the
material.
Even when the constraint is removed, the
material remains deformed
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Types of Material Deformation
Fracture:
The constraint is so intense that it breaksthe material
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Types of Deformations
What are some of the deformations that
a bridge is likely to undergo?
Explain your reasoning.
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Properties
Characteristics that will help
determine how a given materialwill react to a constraint.
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Properties
The reaction of a material to constraints depends onits mechanical properties.
Types of Mechanical Properties: Hardness
Elasticity
Resilience
Ductility
Malleability
Stiffness
Which properties do you believe were considered inthe selection of the building material for the Victoria
Bridge?
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Definition of mechanical properties
Hardness
Ability to resist indentation
Elasticity:
Ability to return to their original shape
Resilience:
Ability to resist shocks
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Ductility:
Ability to be stretched without breaking
Malleability:
Ability to be flattened or bent withoutbreaking
Stiffness:
Ability to retain their shape when subjectedto many constraints
Definition of mechanical properties
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A material can also undergo chemical
changes, such as rusting and corrosion.
What kind of properties should a bridge
possess?
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Other properties
Resistance to corrosion:
Ability to resist the effects of corrosivesubstances which cause the formation of rust,
for example.
Electrical conductivity:
Ability to carry an electric current
Thermal conductivity:
Ability to transmit heat
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Degradation
How will a material age?
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Degradation
The degradation of a materials is the
decline in some of its properties due to
its environment or time
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Degradation of the Victoria Bridge
In 1897 the Victoria bridge was
renovated
To accommodate the increase in thedemand of transportation
To repair the degradation of the bridges
superstructure. The piers only required
minor changes.
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Common materials used in the
1800s
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Wood
Wood is a ligneous (fibrous) material whosebark has been removed.
The mechanical properties differ dependingon the type of wood
Two types of wood Hardwood (deciduous trees)
More resistant to wear and harder than softwood
Softwood (coniferous trees)
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Wood (general properties)
Hardness, elasticity, resilience
Low thermal conductivity
Easily shaped and assembled Light weight
Would these properties be useful duringthe construction of a bridge?
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Wood degradation
Due to its organic nature, fungus,
insects and micro-organisms can infest
the wood.
By varnishing, painting or treating the
wood, we can extend its lifetime.
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Metals
Metals are not usually used in their pure
form, but are combined with other
substances to improve their properties.
This mixture is called an alloy
(homogeneous mixture of two or more
metals)
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Metals (properties)
The properties vary on the metal used
Out of the list provided to you, which metal or alloywould you consider in the construction of the
Victoria Bridge. Justify your answer.
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Please keep in mind
The Victoria bridge is a Tubular Bridge
It is 6 592 feet in length
The superstructure alone weighed 9044 tons. That is 8 204 578.79 kg
Due to the use of the steam engine, temperatures
inside the tube could reach up to 125 F That is 52 Celsius
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Metals Description Properties Cost *
Aluminum White Malleability 2.508$/kg
Soft Lightness
Abundant in nature Resists corrosion
Very good electrical
conductor
Iron Silver in color Ductility 0.21$/kg
Can rust in the
presence of Oxygen
Malleability
Nickel Grey Hardness 1.43$/kg
Malleability
Resists Corrosion
Tin Silvery white Ductility 16.214$/kg
Malleability
Relatively low melting point
(239C)
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Alloys Description Properties Cost*
Cast iron (iron
and carbonmixture)
Made of more than 2%
carbon
Hardness 0.18$/kg
Steel (iron and
carbon
mixture)
Made of less than 1.5%
carbon
Hardness 0.52$/kg
Resilience
Malleability
Brass (copper
and steel)
Mixture of copper and steel
Color varies according to
mixture
Ductility 2.37$/kg
Malleability
Resists Corrosion
Excellent electrical
conductivity
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