Bridge

Bridges have been used since early times to cross natural barriers. These barriers can take the form of streams and rivers. Sometimes the barrier is simply a gap in the terrain – a ravine or canyon. Over time the design of bridges has evolved. In prehistoric times a simple bridge would have been a fallen tree trunk placed across a stream. Nowadays, large bridges are major engineering works requiring a team of designers and an army of construction workers.

Your task is to design and build a large and safe bridge that will be used by people who need to cross a river.

Motivation
To help in the design process, instruct the students to look at the picture on the front of the unit and read the accompanying text.
Alternatively, let the students search the Internet to learn more about the appearance, structure and function of the 4 types of bridges; beam bridge, cantilevered bridge, suspension bridge, and cable stayed bridge, from now and in the past.
Discuss the constraints and functions they will have to take into account.

Note: You are advised not to share this image with students.

While the activity is in progress, encourage the students to relate their
knowledge, skills and understanding to the task at hand by asking:

Which type of bridge will you base your model bridge on?
What different sorts of parts will your bridge need?
How will you ensure that the bridge is strong?
How will you ensure that the bridge is rigid?
How will you ensure that the bridge is stable?
How will you ensure that the bridge is safe to use?
When the bridge is being used which parts will be in compression and which in tension?

When the activity is almost finished, encourage the students to reflect on both the product that they have produced and the processes they have used by encouraging the students to:

Carry out tests to evaluate the performance of the bridge:

• How much load can it take before breaking?
• How much load can it take before deforming?
• Does uneven loading cause the bridge to twist or fall over?
• Will people using the bridge be in any danger?

Record their design by drawing it or taking digital photos of it.
Add notes describing the way the model works and how this might be improved to get better performance.
Describe how to ensure safe use of the model.
Write briefly on what went well in their design task and what they could have done to improve it.

Look at:

Tower Crane (Building Instructions)

Principle Models: Structures (Building Instructions)