Which geometrical shape do you suggest for building bridges? Justify your answer.
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Introduction to Unit
What would our world be like without bridges? There are over half a million bridges in our country alone. Do you know how they work? Why are some curved while others are not? Some are delicate, ingenious and innovative while others are sturdy, functional and dull. Each is the result of centuries of creative design, constant technological development and of imagination held in check by the need for safety, reliability and peer approval. Every bridge grows out of people's needs. The story of bridges is a story of materials. Engineers must consider many things before determining the size, shape and overall look of a bridge. The next time you see a bridge after completing this unit, you will see it with a fresh sense of understanding and a greater level of appreciation of all that went into its construction. Engineering is an art as well as a science.
These lessons will enable the students to learn the history of bridges, identify the basic types of bridges, understand bridge vocabulary, determine the most appropriate type bridge for a specific area based on factors like cost, climate, and function, research and apply information on the internet, understand the construction, explain the forces of compression and tension, use model software to discover the physics in bridge building, create scale drawings, measure and compute math problems accurately, build a model bridge to test load bearing and design a community bridge that will inspire hope and friendship.
This unit is written for grades nine and up average math students. The students in New Haven are from a wide variety of backgrounds but mostly inner city. Their mathematical skills are often below grade level and their interest in school and math is low. There is a pressing need to improve academic performance, proficiency on the CAPT test, and completing high school. The development and use of a curriculum that focuses on the application of math and problem solving of the real life problems in the building of bridges should help inspire and motivate learning.
The unit will begin with the history of bridges, discuss some famous bridges, disasters and bridge facts, explain the basic types of bridges, bridge parts, explore the basic forces at work, truss designs, research and experience the multitude of designs, materials and constructions, find and graph information on bridges, and draw a blueprint. It will conclude with the students designing a bridge for their community that will bridge diversity and promote understanding and community.
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Unit Objectives
1. Describe the common bridge types, including beam, truss, cantilever, arch and suspension.
2. Understand some of the basic design considerations bridge engineers take into account.
3. Understand basic bridge building vocabulary.
4. Understand the function of bridges in modern society.
5. Use the Internet as a tool in research and design.
6. Identify and explain the forces of tension, compression, torsion, shear, and stress and strain as they relate to bridges.
7. Measure, calculate and follow directions accurately.
8. Draw and label tables and diagrams to display information.
9. Design or choose a bridge for a specific cause
10. Explain the principles behind supporting a beam using the truss, arch and suspension method.
11. Understand the history and development of bridges
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The History of Bridges
The history of bridges is fascinating. The oldest and simplest type is the post and beam which the Trojans used over 3,000 years ago. The Roman Empire contributed the arch, cofferdams (encircled watertight walls from which water is removed and bridge foundations dug inside), concrete, and the concept of public works which enables an empire to flourish. The Dark Ages that followed collapse of the Roman Empire was a confusing time of battles, famines, and epidemics. The great bridges of the Romans seemed superhuman to those living in a simple feudal system. Myths sprang up about evil spirits in the streams and bridges. The Roman Catholic Church became the best bridge builders in Europe. The religious orders had the education and travel to research bridges so every bridge had a chapel and an alms (donation) box (for those evil spirits).
In the twelfth century the first London bridge, across the unruly tidal Thames River, was begun with twenty cofferdams to build the piers. There were nineteen pointed arches for a distance of 937 feet. Piers blocked two-thirds of the river which twice daily rose up to 15 feet with the tide. Water rushed through the remaining one third and a dangerous sport evolved called "shooting the bridge" (riding a boat in the fast current between the piers was extremely dangerous). Dozens of tall buildings with shops and homes perched on the bridge. It was a small village on a bridge and the best address in town. By the late 1700's the bridge had to be rebuilt and two more since then.
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Triangles
Truss bridges rely heavily on triangles. Used properly, triangles evenly distribute weight throughout the bridge. Triangles are used on the sides and sometimes even the top of the bridge.