Presentation on theme: "Career opportunity You are a proud junior member of Bridging the gap an up and coming engineering firm. You have been commissioned to approve the construction."— Presentation transcript:
Career opportunity You are a proud junior member of Bridging the gap an up and coming engineering firm. You have been commissioned to approve the construction of a new bridge to be built using 19 th century techniques. Before approving the construction site, you request help from senior members Alexander Ross and Robert Stephenson who have been in the company since 1854 (really senior members). What should you consider before approving the construction site?
What could be considered? What are the characteristics of the site? (elevation, depth of water, current, ice-pack) What is the purpose of the bridge? How big is the expanse of water to be crossed? What kind of bridge to build?
Potential Site Using the topographic map above, what information can you gather about the environment? Port
Purpose of the bridge The bridge must Allow for steam engine trains to cross the river bringing cargo to and from the port
Types of bridges Your company is currently looking at 3 major designs popular in the 1850s: Suspension bridge Wooden Trestle bridge Metal bridge Which type of bridge would you suggest and why?
Engineering Side notes Bridges will always undergo a certain amount of constraints such as… Compression Occurs when a material has a tendency to be crushed or squeezed due to the effects of external forces on an object. Tension Occurs when a material has a tendency to stretch due to the effects of external forces on an object. Torsion Occurs when a material undergoes forces that tend to twist it.
Characteristics Modern Suspension bridges can span up to 2 km Suspension bridges get their name from the deck (roadway, rails) that is suspended by cables strung across the river. Often a truss or trellis structure provides extra support against rippling
How does it work? 1. As the train advances on the bridge, its gravitational force causes the bridge to bend 2. This causes the cables to undergo tension as they stretch to hold up the bridge. 3.Subsequently, the towers, firmly anchored in the ground, will undergo compression, holding up the bridge.
Considerations What are some of the elements that should be considered when building a suspension bridge? a) The length of the bridge b) The weight of the cargo c) The vibrations d) all of the above
Answer: d) all of the above Although the particular region is not renown for its wind, suspension bridges can also have problems with torsion when there is constant vibrations. E.g. Galloping Gertie http://www.youtube.com/watch?v=3mclp9QmCGs
Option 1: Suspension Bridges Based on your site, what are the advantages of this type of bridge? Based on your site, what are the disadvantages of this type of bridge? 1852, St-Johns Newfoundland www.bridgemeister.com
Characteristics Highly inexpensive, due to the abundance of lumber found in the region A trestle is a rigid framework that distributes the weight of overhead objects.
Considerations What is the most important element that one should consider when building a wooden trellis bridge? a) Duration of material b) Cost of the bridge c) Weight of the cargo d) all of the above
Answer: a) Duration of the material In the 19 th century, most of the train tracks were laid over trestle structures to cross rivers and swamps. Although the material was inexpensive at the time, wood does require constant maintenance. On average, an untreated trestle bridge lasts 15 years.
Option 2: Trestle Bridge Based on your site, what are the advantages of this type of bridge? Based on your site, what are the disadvantages of this type of bridge?
Characteristics The Tubular bridge was used in Europe and America for a brief span in the 1800s. Tubular bridges get their name from their appearance. The train basically travels through the middle of a tube made of cast iron.
How does it work? To reduce the amount of deflection (bending), the tubular bridge has many spans.
Engineering Side Note… Deflection is another type of constraint commonly seen in bridges. Deflection occurs when a material is subjected to forces that tend to make it bend.
Considerations What are some of the elements that should be considered when building a tubular bridge? a) The length of the bridge b) The type of engine used c) The material used d) all of the above
Answer: d) The length of the bridge is highly important. Depending on the material used, it will dictate how many sections are required. The type of engine used in the 1850s is the steam engine. This type of train is fuel by the combustion of wood.
Option 3: Tubular Bridge Based on your site, what are the advantages of this type of bridge? Based on your site, what are the disadvantages of this type of bridge? Construction of the Victoria Bridge