"Bridging the Gap" Material Selection

1. "Bridging the Gap" Material Selection

2. 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.

3. The Victoria BridgeA quick overview of the Tubular design

4. 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.

5. What to consider? • What should one consider before selecting the construction materials?

6. 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)

7. Constraints What external forces are at play?

8. Constraints • A constraint is the effect external forces have on a material/object/system. • Examples of constraints: • Pulling an elastic band • Squishing a sponge

9. 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?

10. 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

11. 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

12. Types of Constraints • Which constraints would a bridge most likely be subjected? Explain your reasoning. • 5 Constraint reminder: • Compression • Tension • Torsion • Shearing • Deflection

13. Deformation Ways that materials react to the constraint

14. 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?

15. 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.

16. 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

17. Types of Material Deformation • Fracture: • The constraint is so intense that it breaks the material

18. Types of Deformations • What are some of the deformations that a bridge is likely to undergo? • Explain your reasoning.

19. Properties Characteristics that will help determine how a given material will react to a constraint.

20. 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?

21. Definition of mechanical properties • Hardness • Ability to resist indentation • Elasticity: • Ability to return to their original shape • Resilience: • Ability to resist shocks

22. Definition of mechanical properties • 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

23. A material can also undergo chemical changes, such as rusting and corrosion. • What kind of properties should a bridge possess?

24. 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

25. Degradation How will a material age?

26. Degradation • The degradation of a materials is the decline in some of its properties due to its environment or time

27. 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 bridge’s superstructure. The piers only required minor changes.

28. Common materials used in the 1800’s

29. 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)

30. 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?

31. 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.

32. 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)

33. 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.

34. 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