Critical Thinking

1

Bridges and Bridge Design

• Critical Thinking
• in Engineering Process

2
Introduction to the different types of bridges

• beam bridge
• suspension bridge
• arch bridge

3
Why are there different types of bridges?

• The major difference between the three types of
  bridges is the distance that they can cover in a
  single span. Span is the difference between two
  supports. Each of the different types of bridges
  holds weight in different ways.

4
Beam Bridge

• A beam bridge is basically a rigid horizontal
  structure that rest on two supports, one located
  at each end of the bridge as shown in Figure (a).
  A simple beam bridge is flat across and supported
  by two ends.

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What happens to the bridge when a load is put on
the bridge?

• When the load pushes down on the beam the top
  edge is pushed together or compressed, while the
  bottom of the beam is stretched or is under
  tension.

6
What factor(s) should you consider when you build
a beam bridge?

• The beam must be strong enough so that it doesn't
  bend under its own weight and the added weight of
  the traffic crossing it.

7
Arch Bridge

• An arch bridge is composed of a curved structure
  with abutments on each end.

8
What happens to the bridge when a load is put on
the bridge?

• The weight of the load is carried outward along
  the curve of the arch to the abutments at each
  end of the arch. The abutments also keep the end
  of the bridge from spreading outward.

9
What factor(s) should you consider when you build
an arch bridge?

• The arch bridge is always under compression
  because the weight of the deck is pushed outward
  along the curve of the arch towards the
  abutments. The rise in the form of the curved
  arch causes the vertical load to have a
  horizontal thrust.

10
Suspension Bridge

• The suspension bridge literally suspends the
  roadbed from huge cables, which extends from one
  end of the bridge to the other. The cables are
  attached to two tall towers and are secured at
  each end by anchorages.

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What happens to the bridge when a load is put on
the bridge?

• The cable carries the weight on a suspended
  bridge to the anchorages that are imbedded in
  solid rock or massive concrete blocks. The cables
  are spread over a large area in order to evenly
  distribute the load inside the anchorages to
  prevent the cables from breaking free.

12
What factor(s) should you consider when you build
a suspension bridge?

• The anchorages help to stabilise the bridge.
  Therefore, the tower must be embedded to earth
  firmly. In such a way, the cables transfer the
  forces to the towers which carry the forces
  directly into the earth where they are firmly
  imbedded.

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Project 2Part A - Custom Bridge 

• Explanation
• The students will research and design their own
  bridge using the Internet. After their research
  of bridges is complete they will come up with
  their own design and construction of a bridge.
  Students are to use the pre-cut pieces of wood,
  glue, and base. Overall dimensional constrains
  will be given at a later time. Duration for this
  project is 6 weeks.
• Student Requirements
• - Internet Research 
• - Select materials
• - Create a design
• - Determine size
• - Create a full scale set of plans with
  dimensions
• - Determine and learn required tools and machines
  to create your stool.
• - Build your bridge 
• Total Points Possible
• Complete custom stool    100 Pts.

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Part B Bridge Construction Term Papers 

• Explanation
• Students will write a short term paper about
  their process in creating their bridge. This
  paper is dived into three areas. Section 1 is
  about student research and design, material
  selection, advantages and disadvantages of
  materials, and cost of materials. Section 2 is
  about the actual bridge building making process
  in the lab, tool, machines, and safety. The final
  part is a summary of the whole process and the
  completion of a shop stool. 
• Student Requirements
• - Students research established stools an
  Internet
• - Students research material selection
• - Students explain why they selected their
  materials
• - Students write first draft of term paper
• - Students revise term paper
• - Students hand in final draft of term paper (3
  pages). 
• Total Points Possible 
• Shop Stool term paper        100 Pts.

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Part C - Bridge Testing 

• Explanation
• Students will test their bridge for maximum
  strength, durability, and materials cost
  efficiency, which means that the most points will
  be awarded to the bridge that holds the most
  weight with the least structural damage and least
  materials.
• Student Requirements 
• To have created a high quality bridge that will
  have the most weight.
• Total Points Possible 
• Total   100 Pts.