Presentation on theme: "The Final Test… Before the opening ceremony in 1859, the Victoria Bridge underwent a safety test. The test consisted of an 18 platform cart train filled."— Presentation transcript:
The Final Test… Before the opening ceremony in 1859, the Victoria Bridge underwent a safety test. The test consisted of an 18 platform cart train filled to 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.
The Victoria Bridge A quick overview of the Tubular design
Situation The Victoria Bridge was a technological marvel, yet the engineers in charge knew less about materials than we do today. Justify which material you would have chosen for the project.
What to consider? What should one consider before selecting the construction materials?
What to consider? What are the stresses/external forces the material will undergo? (Constraints) How do we want the material to react to such stresses? (Deformation) How will the material react? (Material properties) Will the material last a long time? (Degradation)
Constraints What external forces are at play?
Constraints A constraint is the effect external forces have on a material/object/system. Examples of constraints: Pulling an elastic band Squishing a sponge
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?
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
Types of Constraints Torsion When a material is subjected to forces that tend to twist it Shearing When a material is subjected to forces that tend to cut it Deflection When a material is subject to forces that tend to bend it
Types of Constraints Which constraints would a bridge most likely be subjected? Explain your reasoning. 5 Constraint reminder: Compression Tension Torsion Shearing Deflection
Deformation Ways that materials react to the constraint
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?
Types of material deformation Elastic: When the constraint leads to a temporary change in the shape or dimensions of the material. When the constraint is removed, the material returns to its original form.
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
Types of Material Deformation Fracture: The constraint is so intense that it breaks the material
Types of Deformations What are some of the deformations that a bridge is likely to undergo? Explain your reasoning.
Properties Characteristics that will help determine how a given material will react to a constraint.
Properties The reaction of a material to constraints depends on its mechanical properties. Types of Mechanical Properties: Hardness Elasticity Resilience Ductility Malleability Stiffness Which properties do you believe were considered in the selection of the building material for the Victoria Bridge?
Definition of mechanical properties Hardness Ability to resist indentation Elasticity: Ability to return to their original shape Resilience: Ability to resist shocks
Ductility: Ability to be stretched without breaking Malleability: Ability to be flattened or bent without breaking Stiffness: Ability to retain their shape when subjected to many constraints Definition of mechanical properties
A material can also undergo chemical changes, such as rusting and corrosion. What kind of properties should a bridge possess?
Other properties Resistance to corrosion: Ability to resist the effects of corrosive substances which cause the formation of rust, for example. Electrical conductivity: Ability to carry an electric current Thermal conductivity: Ability to transmit heat
Degradation How will a material age?
Degradation The degradation of a materials is the decline in some of its properties due to its environment or time
Degradation of the Victoria Bridge In 1897 the Victoria bridge was renovated To accommodate the increase in the demand of transportation To repair the degradation of the bridges superstructure. The piers only required minor changes.
Common materials used in the 1800s
Wood Wood is a ligneous (fibrous) material whose bark has been removed. The mechanical properties differ depending on the type of wood Two types of wood Hardwood (deciduous trees) More resistant to wear and harder than softwood Softwood (coniferous trees)
Wood (general properties) Hardness, elasticity, resilience Low thermal conductivity Easily shaped and assembled Light weight Would these properties be useful during the construction of a bridge?
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.
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)
Metals (properties) The properties vary on the metal used Out of the list provided to you, which metal or alloy would you consider in the construction of the Victoria Bridge. Justify your answer.
Please keep in mind… The Victoria bridge is a Tubular Bridge It is feet in length The superstructure alone weighed 9044 tons. That is kg Due to the use of the steam engine, temperatures inside the tube could reach up to 125 F That is 52 Celsius
MetalsDescriptionPropertiesCost * AluminumWhiteMalleability2.508$/kg SoftLightness Abundant in natureResists corrosion Very good electrical conductor IronSilver in colorDuctility0.21$/kg Can rust in the presence of Oxygen Malleability NickelGreyHardness1.43$/kg Malleability Resists Corrosion TinSilvery whiteDuctility16.214$/kg Malleability Relatively low melting point (239C)
AlloysDescriptionPropertiesCost* Cast iron (iron and carbon mixture) Made of more than 2% carbon Hardness0.18$/kg Steel (iron and carbon mixture) Made of less than 1.5% carbon Hardness0.52$/kg Resilience Malleability Brass (copper and steel) Mixture of copper and steel Color varies according to mixture Ductility2.37$/kg Malleability Resists Corrosion Excellent electrical conductivity