Bridge Building Series - Truss Bridge 1

Truss bridge building instructions 1

We’ll make different truss bridges using two different materials - foam cubes and cut drinking straw pieces.

Design Rules for both bridges:

1.      Bridge must span 10 inches (25 cm)

2.      Bridge must have a place to attach a small cup in the center of the span (preferred).

3.      The ends of the bridge are not taped onto the support structure.

Bridge 1 – Marshmallow/foam cubes/cheese balls & toothpicks

NOTE: The best material for this project is foam cubes. However, a container of foam cubes can get very expensive (I've paid $27.49 for a container of 105 foam cubes), so if you can find more affordable ones, please let me know.

I've done this project with marshmallows, and it's doable (for intermediate grades). And cheese balls get messy, but doable as well.

Supplies:

·         A bag of marshmallows, foam cubes, or cheese balls

·         A box of toothpicks

·         Tape

·         Small cups

·         Paper clips

·         Weights – pennies, paper clips, etc. Anything is OK as long as they weigh the same. You want to compare how much different bridge designs can support

    

Instructions:

1.   Create a square with four foam cube pieces and toothpicks. Create 3 more. Put them together to create a cube. 

2.   Create several more cubes and put them together until you reach 10 inches in length. Remember, your bridge must be longer than the span it needs to bridge (add an inch or two to the total length of your bridge).

  

3.   Place the bridge between two desks, tables, chairs, etc.

4.   Hang a small cup in the middle of the bridge (use hole puncher and paper clips) and load it with pennies, paper clips, etc. to weigh it down and test its strength.

~same number of coins in the cup as the beam bridge project

added another cup of coins

added more coins to each cup

Again, this project works best with these foam cubes. I purchased from Amazon, but they are pricey. I did find some smaller foam cubes from the Dollar Tree store, and they worked well. But it's very difficult to find them consistently. You can see them on their online store, and the store managers don't seem to know when or if they'll ever get another shipment. So, if you find another source of reasonably priced foam cubes, please let me know.

Magnificent Marshmallow Marvels 1 - Adventures in Civil Engineering

In 1991 when I was working for Bechtel in San Francisco, I participated in this program called Engineer’s Week. It took place in February, if I remember correctly, and it was around Valentine’s Day time. Bechtel encouraged their engineers for volunteer to participate in this outreach program. We went out to different schools and spent a couple of hours talking about what we did and led the students in a fun, hands-on project which supposed encouraged the students to see Math and Science as something other than hard or boring.

There were many projects to choose from, but I choose this one because I thought it would be fun and it was easy to get hands on the materials (for Engineer’s Week, I think we didn’t have to do anything except pick up the project supplies from an admin and show up at school). I don’t remember what the project was called, but this is what I call it.

Magnificent Marshmallow Marvels – Adventures in Civil Engineering

For this project, you need mini marshmallows and toothpicks. A lot of toothpicks. I suggest the Dollar Store/Dollar Tree, etc. for the toothpicks because you can get a box of 1000 toothpicks for $1 (you’d be amazed at how many boxes of these toothpicks a kindergarten or a 1^st grade class will go through).

I start the class by talking about living in California, earthquakes in general, then why earthquakes occur and plate tectonics (depends on the grade). I always have a tangible premise for the project. Most often, we’re trying to build inexpensive, yet safe housing for the poor in countries such as China, Chile, etc. The team that builds the safest and tallest house/building wins.

Supplies:

1. Mini marshmallows
2. Toothpicks
3. A shakable flat surface (bigger than shoe box size plastic container lids work great) 

Instructions:

1.       Create a cube with marshmallows and toothpicks.

2.       Create a body-centered-cubic cube with marshmallows and toothpicks.

3.       Place these two cubes on a flat, shakable surface (most often, it’s a plastic container lid I find in class), secure them in place (holding on to them with the lid or lightly tape the bottom toothpicks to the lid) and shake them to see how they react to an “earthquake” of your creation.

4.       Try to build another level on top of the ground level housing.

  

5.       Without much effort, students are able to easily build 2 level high structures, but anything beyond that is a challenge because marshmallows are actually terrible building material (This is why marshmallows are used. It’s inherently and deceptively challenging because they are too stretchy).

6.       To build beyond two levels, first the buildings must be reinforced in the bottom with two toothpicks vertically used in the each corner of the ground floor cube. This applies to both cube designs.

7.       There are infinite ways to build higher than two levels. Try different ways and see what you and your students/kids can come up with.

The key concepts I talk about in class are:

1.       Fatigue Failure – there are some great definitions on the web, but I tell my students that it’s a fancy engineer’s way of saying it just got tired after repeated loading and unloading of weight (in this case, it’s the weight of the building itself).

2.       Dissipation of forces – again, there are some great definitions on the web, but I tell my students it’s spreading out the weight or the burden. If one person is holding up something very heavy, it’s much easier if two or three people share the burden of holding up the same weight (the example of two toothpicks in the same corner instead of just one).

Here are some other neat structures you can build with your kids/students.

Experiment and have fun!