Rainbow Bridge STEM Project

It’s March and that means that mischievous leprechauns are sneaking around looking for a spot to hide all of their golden treasures, what a perfect time for a St. Patrick’s Day Activity.  Everyone knows to look for a pot of gold at the end of the rainbow, right?  So what if we try to trick that sneaky leprechaun into leaving his gold right where we want it?!? In this challenge we are going to add a colorful twist to a bridge building activity and build a rainbow colored bridge to try to entice the leprechaun.  The more weight the bridge can hold the better off we will be, so let’s try it!  

Build a Rainbow Bridge STEM Challenge

Rainbow Bridge STEM Activity

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Why Build a Rainbow Bridge?

Building bridges that serve a specific purpose, such as supporting weight, is a fun, easy STEM challenge with some powerful learning opportunities.

In this activity we are building a rainbow bridge. By incorporating the rainbow aspect, we include some powerful lesson plan connections.

First, this project makes an excellent STEM Spring Activity. Spring projects often have rainbow themes.

St. Patrick’s Day is in March and we all know Leprechauns love their rainbows! That makes this project a fun tie in to this holiday. For another fun St. Patrick’s Day activity, check out our Leprechaun Trap.

In Norse Mythology, the rainbow bridge is known as Bifrost and connected Earth (known as Midgard) to Asgard, the home of the gods. Only the gods could cross this bridge. It is believed the mythology of the rainbow bridge Bifrost is connected to the Milky Way. This gives you two powerful lesson plan ideas for some hands on learning in either a Viking Unit Study or even a Space Unit Study.

Whether you are doing this project for Spring or St. Patrick’s Day, a Viking Unit Study, or just as a cool project that looks incredible, bridge building is an excellent STEM challenge for your students.

Key Question: What is a Bridge?

Before we get building I wanted to make sure we understand what a bridge is and the different ways that bridges are constructed. A bridge is a structure built to join two disconnected areas.

It might be over a body of water, across mountains or over a cityscape.

The Science Behind Strong Bridge Designs

Bridges depend on two different forces to make it stable enough to carry the load that crosses it, compression and tension. 

Compression squeezes materials together and allows weight to be spread across it. Think of a spring, when you push the ends of a spring together (or compress it) the spring becomes shorter and the spirals are closer together making the structure stronger. 

The second is tension which expands materials forcing the stresses to be on supports of a structure. Think about what happens with a rope in a game of tug of war.  The outside forces, in this case the people at either end  pull the rope tight making it rigid. Different bridges use these forces in different ways to make them strong and stable. 

What are some types of bridges that we might gain inspiration from to trick our little leprechaun? Here are a few…

Arch Bridge:

An arch bridge uses a curved structure which supports from above by spreading the load from the top across to the abutments on either side of the arch. 

Beam Bridge:

Beam bridges are one of the simplest forms of bridge building.  They consist of a horizontal beam and supports on each end.  The load is directly carried by those vertical structures.  

Truss Bridge:

Truss bridges use a series of triangle supports or trusses to distribute a load across large spans.  You will often see them used as railroad bridges.  

Now that we have some basic working knowledge of bridges, how can we use that information to build a rainbow bridge to attract our friend the leprechaun and all of his shiny gold coins? 

When I am working at home on a fun project I like to let the kids’ minds go where they will and let their creativity run free.  In the classroom it is necessary to put more parameters on the builds and have it a little more structured. 

What do we need?

There are all sorts of rainbow materials out there, I decided to stick with easy to find items you likely already have in your classroom, crafting drawer or tinkerspace.

Rainbow Bridge Project Construction Supplies

Materials for your Rainbow Bridge:

Construction Paper
Craft Sticks
Pipe Cleaners

Possible Connectors: 

Glue Gun
Glue Sticks or School Glue
Paper Clips

Working Tools 

Paper & Pencils


Pot of Gold
Gold Coins

Classroom Worksheet

Members of the STEAM Powered Family can download a worksheet to go along with this classroom project. The printable includes information on the different bridge types, how to make paper stronger and a STEAM design process sheet to fill out. Simply enter your email in this form to unlock the printable.

Rainbow Colors

Just as a quick reminder, the order of the rainbow colors is ROY G BIV – Red, Orange, Yellow, Green, Blue, Indigo, and Violet.

Craft Stick Bridge Challenge

Our first attempt was a dream big moment. I gave my daughter free reign to come up with a rainbow bridge that she thought would attract a leprechaun to bring his gold.  She decided on a craft stick bridge challenge and chose to build a truss bridge with the colored popsicle sticks, and (no surprise) her connector of choice is a glue gun.  (As with any project hands on help may be necessary with tools like a glue gun, safety first!)

Craft Stick Bridge in Rainbow Colours
Rainbow Craft Stick Bridge

To start, she built a series of trusses (triangles) deciding on one color for each triangle. 

The deck part of her bridge is a beautiful rainbow path.  She used alternating popsicle sticks in every color of the rainbow.  Then she repeated the pattern three times connecting the deck on the underside with additional popsicle stick cross beams. 

She opted to stack her trusses to raise the bridge platform off the ground and to build a rainbow staircase and rainbow colored and St. Patrick’s day  embellishments to entice the little leprechaun to climb onto the bridge. 

She also added a small ladder to the backside for easy access to grab the treasure. 

The trusses make the bridge nice and strong and it easily held a pot of gold coins.  

Paper Bridge Building Challenge

Our second attempt is the paper bridge challenge.  This is the challenge that works well in the classroom, it has more structure and defined parameters.

For classroom STEAM projects we use the STEAM DESIGN PROCESS: Ask, Imagine, Plan, Create, Test, Improve.  Working through the design process allows the students to really think through the problem or challenge, thoughtfully collaborate on design and construct with a set goal and plan in place.  

Our key question: How can we build a strong bridge using only 6 sheets of construction paper (one in each color of the rainbow) and one chosen connector? (I like to let the groups choose what connector that they think will work best in their design).  Your goal is to make a bridge that will hold a plastic pot and as many pennies as we can add without the bridge failing.  

How To Build A Strong Bridge with Paper

So how can we possibly make a strong bridge with just paper?  Here’s a little brainstorming on how we might make paper stronger.

How to make a strong paper bridge ideas
Paper Bridge Construction Ideas

Fold It!

Folding paper into different shapes and thicknesses will give the paper more structure and strength.  A tip: Run your ruler along the folds to make them strong folds (this is called scoring the paper)

Roll It!

Rolling paper into a tube shape makes it stronger because it adds layers to the paper to make it more rigid. 

Stack It!

Stacking paper into a pile gives it added strength by making it thicker. 

Weave It!

Whether you use plain strips of paper or you fold pieces into thicker pieces and then weave them together, the act of crossing paper over and under other pieces lets all of the pieces work together to give the paper more strength. 

Twist It!

Rolling a piece of paper into a long stick and then twisting that stick gives added strength because you’ve essentially stacked those twists on top of each other.

Crumple It!

Crumpling paper into a ball or other shape gives it more structure and therefore more strength.  Connecting crumpled papers could be the same as stacking rocks! 

Paper Bridge Designs

Paper Bridge Design #1: Folding and Rolling

In our first bridge we tried some simple folding and rolling techniques to try to make a beam bridge. Our only connector on this bridge was a plain school glue stick.  

Paper Bridge Design 1
Paper Bridge Design #1

We decided early in the design process that an entire piece of paper wasn’t necessary and we could stretch out materials by cutting the paper.  All of the decking strips are a half a piece of paper cut lengthwise and then folded in thirds. 

The same cutting and folding technique was used for the arches we placed above the decking to keep the sides in place. 

For the support posts, we rolled the other half of the sheets into tubes about the width of paper towel tubes. 

To attach them to the bridge we cut and folded flaps so we had something to connect the two pieces together. 

Paper Bridge Connectors
Paper Bridge Connectors

The bridge looked nice but ended up not being as strong as the other designs. 

Paper Bridge Design #2: Rolling Tighter Paper Tubes

For this post and beam bridge we decided to use the rolling technique again, but to roll tighter, smaller tubes. 

Paper Bridge Design 2
Paper Bridge Design #2

Again we cut the paper, this time cutting off one third across the width before we got started. This method of rolling the tubes longer and smaller made the tubes really strong because we ended up with so many layers in each one. 

To keep the rolls nice and tight we decided on clear tape wrapped around each end of each piece. 

The decking consisted of one roll per color of the rainbow. We flipped them seam side up and taped across the width of the tubes.  A strip of tape at each end and one in the middle.

To make support beams we tightly rolled the remaining pieces of paper and taped them the same way as the longer ones. 

From there we lined three tubes together and taped them securely together, then taped those three section posts to the underside of the bridge.  Then repeated with another three section post on the other end. 

This design was great! Nice and sturdy and looked a lot like a rainbow too! 

Bridge Design #3: Arch with Folding and Stacking Paper

For the third design we really wanted to try an arch, because a rainbow is naturally arched.  There was a lot of discussion about how we could make the paper strong enough to hold the pot of gold.  We decided on a folding and then stacking method to make the paper thicker and stronger. 

Paper Bridge Design 3
Paper Bridge Design #3

We started by cutting the paper in half across its width.  Half of the paper would be used to make the rainbow and half folded and taped to make the base stronger.

We took one pile of the paper and folded each piece into a fan or accordion and taped it at each end. For the second stack of paper we spread it out a little to make an overlapping rainbow path and then taped it together so that it stayed flat. 

Now for the rainbow! We started with the bottom of the rainbow with the blue and folded the two ends out flat so we could secure it to the paper, arched it in the middle and then taped it in place. 

We repeated this same process for each color of the rainbow using a little less of a flap on each side each time to make room for the growing stack of paper.

The result definitely said rainbow, it turned out so cute! It was surprisingly strong for being just arched paper and easily held that pot of gold! .  If we were going to do this at home I would love to see some cotton added to each side for clouds!

Troubleshooting and Tips

This project is so fun and colorful!  I love to see all of the different design ideas come to life.  As with any project we want to be ready for students running into issues. 

Some challenges you may run into – your chosen connector isn’t holding.  Glue can be tricky – it holds nicely but takes some drying time to hold well. Paper clips hold nicely but can slip under pressure.  Staplers can be hard to get into tight spaces and could rip through the paper under tension.  

These are great talking points to have a follow up discussion after the competition.  What designs held up the best, what techniques made stronger structures.  Let’s not forget our friendly neighborhood leprechaun either – what bridge is the most colorful and attractive to a leprechaun looking for a rainbow to hide his pot of gold!  

I hope these ideas get you excited about this colorful challenge! 

Happy St. Patrick’s season everyone!  May the luck of the Irish be with you! 


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