Structures

Bridges are super cool structures that can be used for all sorts of things. They can be used to span two sides of a canyon to allow cars to drive over. They can be used to span an area where the ground is very un-level and a level span is needed to move goods such as coal or water. They can be used to provide a pass over and under so that opposing traffic does not have to meet on the roadway. They can be used to create an isolated entrance like in a castle. Bridges have many uses and can be studied for their strength and design to make stronger, simpler, or more efficient designs. If you are interested in any of the stuff described above consider looking into civil engineering (civil engineers design, figure out how to build and how to maintain all sorts of different structures), architecture (architects are people who design buildings, bridges, etc…) or transportation processes (transportation is moving things from one place to another, aqueducts are an amazing example of moving water simply using gravity for great distances).

Experiment Title:

Bridges, can I build one strong enough?

Objective:

The objective of this lab is use the basic principles of bridge/strength design based on the strength of different shapes in order to build you own bridge that can support the weight of a car, a train, or a squishy meteorite traveling very slowly (bean bag).

Background on Strength of Shapes:

When buildings or structures are designed they typically create a geometric shape with their general shape. Think about a house, a house is typically a rectangular block or a cube (a rectangular block has 2 sides that are equal in height and width and 4 sides that are equal in height and width, a cube all six sides are equal in height and width).

Rectangle (rectangular block) - A rectangular structure with the long side on the bottom is very stable when resting on the ground.  An object that has a rectangular shape, with the long side down, is not easy to push over.  Tables, desks, and many buildings are examples of such a stable structure.  Rectangular shapes are especially good for buildings because they are easily divided into rectangular rooms.  Rectangular rooms are ideal for furniture placement and saving space. A narrow rectangular structure with a short side at its base is not very stable.  Structures having this structure are easy to push over.  A television aerial support pole is an example of a narrow rectangular structure.  Often these narrow structures must have their bottoms sunk into the ground to give added support, or be supported by outside wires or buttresses.

Square (cube) - A square structure is a stable structure that is not easy to push over.  It has flat surfaces, which may make it useful for some functions.  Some tables, TV sets, stools, tables, and smaller houses are square structures.

Triangle (pyramid) - A triangular structure is very stable because it has a wide base.  The Eiffel Tower is a good example of a triangular structure.  Occasionally, triangular structures, with a point at the bottom, are used for hydroelectric power towers.  Such an inverted triangular shape is strong, but not stable and must be supported by extra guy wires to keep the tower from falling over.  This shape enables many power lines to be strung across the wide top, while keeping a safe distance between the lines.  Very little space is needed on the ground for such an inverted triangular structure.

Circle (sphere) - Circular structures, or more accurately, spherical, are ideal structures for submersibles, which must support the tremendous external water pressure.

Materials

• Gum drops
• Cardboard blocks
• Keva Planks
• Legos
• toothpicks
• lab notebook

Method

Prepare Experiment

1. Collect your materials from your STEM kit and from your teacher
2. Write out your experiment in your lab notebook
3. Draw a detailed design for your bridge (this way you can look back at your idea and build it as you initially intend to verses winging it.

Run Experiment

1. Using your bridge design
2. Write out your experiment in your lab notebook
3. Draw a detailed design for your bridge (this way you can look back at your idea and build it as you initially intend to verses winging it.
4. From here, going to the various stations set up in the lab space and build your bridge design using the different materials
5. Build your design and test its strength with the strength testing materials at that station
6. Write down your results
7. If you have time, try changing your design and see if that increases or decreases the strength of your bridge
8. Move to the next station and repeat

Analyze Data

• Which materials made for the best bridges?
• Which materials made for the weakest bridges?
• Did changing your design help or hinder the strength of your bridge?

Conclusions

Different shapes have their own strengths and can be used in conjunction with one another to create very strong or very week structures. The shapes used in the structure do affect how strong a structure is but so do the materials that are used in the structures composition. The key points to take away from this lab are simple: structures have many facets that make them strong but can also acts as weaknesses. A good design and good materials can make a very strong structure.

Make It Your Own

Think about the different stations that we set up and the different materials that you were allowed to use, what do you think you could do with the materials if you were allowed to combine stations? How about if you were able to do your own strength testing, what would you do to test the strength of your different materials and designs?

Extension Activities to do at home

With your parents’ permission go home and use various materials from the kitchen to make a few more prototypes of your bridge. See if your parents have some rubber bands. Rubber bands may seem weak but can make very strong bridges if given the chance.