How to build a Straw Bridge – STEM Activity

Stem Straw Bridge Blog Title

Who isn’t fascinated by bridges ? Staying in California gives us the opportunity to drive across different bridges and be amazed at these engineering marvels. So, we decided to learn more about the various types of bridges for today’s stem activity, design and build a straw bridge model and test it by placing some weight on it.


To begin the activity, we looked at a couple of pictures of various types of bridges ( Golden Gate Bridge in San Francisco , The Tower Bridge in London , Sydney Harbor Bridge, and different bridges especially in California HERE ) and I asked my kids.

  • What shapes do you see in these structures?
  • Which parts of the structure do you think help most for making it really strong? Why?
  • Which shapes do you think most help the structure become strong?

Introducing the Mathematical Idea

We talked about how triangle is the strongest shape and used in most of the bridges. And we tested it ourselves before building the bridge model. Kids quickly grabbed some toothpicks and clear tape and made different shapes to check and see which shapes are rigid or flexible when gently pushed on one corner.

I then showed them a simulation of the strength of different shapes in a building HERE.

Types of Bridges

Now it was time to look at the different types of bridges and the forces acting on them before beginning to build one : Beam, Arch, Cable-Stayed, Cantilever, Suspension and Truss.

Beam: Beam bridges are the oldest bridges known and prove to be the easiest to design and build. These bridges are horizontal and supported at the end of each side. This form of bridge rests on the top of the beams that pressing straight down on both ends of the bridge.

Arch: Arch bridges are arch-shaped. They have supports on each end, and the both ends of the abutments bear the center weight of the bridge.

Suspension: Cables are used for carrying suspension bridges. The cables are suspended from towers connected to cofferdams. Such blocks are deeply mounted. in the water’s surface or body.

Truss: Truss bridges have a sturdy deck and a frame of girders on the sides. They are build either by putting many triangle frames together or by using a pyramid style frame.

Cable-stayed: Closely resembling suspension bridges, cable-stayed bridges are supported by cables except they use fewer cables. The towers that hold the cables are much shorter than suspension bridges. (Tatara Bridge) 

STEM Activity – Build a Straw Bridge

Kids were eager to start their STEM activity and build a straw bridge of their own. They first made a design on the paper, discussed and tweaked it, and went on to build their own bridge, tested it and then made modifications to make it stronger.

It was time to test both the models.

and both the models did fairly well under the weight.

Further Discussion

We then discussed about the engineering element behind the design of a bridge.

  • How you think this information is used by engineers and architects while they are building ?
  • Which sorts of events are likely to push and pull on real life structures ( Gravity, water, wind etc ).
  • What factors the engineers take into consideration before constructing the bridges.
    • How far does the bridge need to stretch? A very short span or fairly long distance.
    • Does the location where a bridge is being build a crucial factor ? Is the ground firm enough to take large abutments for an arch? Is there a good bedrock where suspension cables can be anchored ?
    • If the bridge needs to cross a river, how can piers and towers be safely plunged into its bed so the flowing water doesn’t scour them away.
    • How much load the bridge has to bear ? Will it hold railroads, cars and pedestrians.
  • How will architects and engineers decide to have rigid structures ? When could they want them to be flexible?
    • Most bridges are designed to be primarily rigid, but with an expected amount of flexibility so that they can withstand strong wind or earthquake.
  • How can engineers increase the ability of a building to withstand earthquakes ? What is a cross brace ?
    • Using the square shape kids made before, add a 5th toothpick diagonally. The shape is now divided into small triangles and gives the initial square model more stability. This is called cross brace.

The kids then watched the video to learn more about the strength and weakness of each type of bridge.

If you’re looking for more STEM activities for kids, check them out HERE.

6 Replies to “How to build a Straw Bridge – STEM Activity”

  1. What a fun project! This takes me back to middle school, when we had to design a bridge and compete in class to see which bridge could support the most weight!

  2. I am going to try this with my two little ones! They love these types of activities and I love keeping them busy 🤣

  3. Looks like a great project. We were just learning about bridges in my history of technology class — maybe this will help to reinforce some of the basics that I learned and help teach my kids.
    Thanks for sharing!

  4. This looks like an amazing stem activity. Hope I can do it with my toddler, we will have to rely greatly on instructions! Great post!

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.