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Everything You Need to Know about Building Bridges

Not too long ago I wrote a post about building bridges and my focus was on one style of bridge for each grade level. While looking through my array of bridges I realized I had even more types that were not going to be part of that post.

Note to self: Add a post about the other bridges some day! Today’s the day!

I will add that building bridges is quite exciting. Kids love to drive little cars across them and they love to add weight to the bridge to see how well it will support it.

Let’s get going- with kinds of bridges and the mistakes I made in the beginning! Tips for not making those same mistakes will be included!

STEM Challenge- tips and tricks for building bridges in STEM class! This post features many different types of bridges.

The First Bridge

The first bridge we built was … interesting. My part was to determine the materials we would use and also determine what the bridge would span. I decided each team needed two boxes. The bridge would rest between the boxes – what I call the span or the roadway.

Check the photo below- we taped two tissue boxes about six inches apart.

This is a bridge made from straws, toothpicks, string, and paper clips. They were quite flimsy and only a few groups were successful.

My mistake: Those boxes we used were not the best bridge span. We also had a rule that the ends of the bridge could not be attached to the boxes. They collapsed in the middle easily.

So, before we tried this again I re-thought the span and the materials. Take a look below.

STEM Challenge- Build a bridge that will span a six-inch gap and hold weight. Check this post for the details.

I took toothpicks out of the materials – due to a safety issue (for me). Students (these are 5th graders) will try to pierce the materials with toothpicks and I really don’t want to see them accidentally pierce their fingers! And, I changed the bridge span device to a plastic bin. These bridges are longer- we built them the length of the bin and we used the string in very clever way. Most teams opted to use the string as a form of tie-down which added stability to the span. These held a lot of weight!

Marshmallows

This is the one we call the marshmallow bridge. The materials are toothpicks and marshmallows. Yes, I know I just said I didn’t like using toothpicks. But here the students are only stabbing a soft marshmallow- not a straw or cardboard box.

What do you think my mistake was with this one? If you think it is using marshmallows as a building material, you are partly correct!

The real mistake is buying good marshmallows. Buy the store brand and open them the night before you use them. The stiffer the marshmallow the better these bridges work!

You can see in the photo below that the bridge completely collapsed as the students tried to move it . Those really soft marshmallows are hard to work with!

Originally, this challenge was also tried using two tissue boxes. We did discover that the bridge works better using the plastic bins.

Notice the one in the photo below has sides in triangle shapes!

STEM Challenge- Build a bridge that will span a 9-inch gap using marshmallows! Check this post for the details.

This marshmallow bridge is fun. Have wet washcloths on hand to help clean up their gooey fingers and your tables!

Index Cards

You cannot get much easier than this one. You just need index cards and something to use for adding weight to the bridge.

My mistake with the rules on this one was something I did not foresee as a rule we needed. The first class that tried this took several cards, rolled them into a tube, and then sat the weight bowl on top of the cylinder. We completely filled the bowl with pennies and that cylinder would not collapse.

But, is that a bridge?

STEM Challenge- Build a bridge using only index cards. It must hold weight! Check this post for the details.

Well, no. So, we had to back up and talk about what this bridge would resemble. It needs to have a roadway. Several columns can hold the roadway aloft. Ok, the kids got busy and had a new bridge in 2 minutes. They made a long roadway with about 5 rolled card columns and placed the weight bowl on top of one of those columns.

Clever students, right? So we changed the rules again. You do not drive your car only on the columns holding it up. The weight bowl has to be placed on the actual roadway! This (finally) turned out to be very challenging!

Suspense, anyone?

I wanted to build a suspension bridge for a long time and had to build one on my own first. I needed to see if this was a task students could tackle.

Here is what I found. Tape will not hold the bridge pieces together. The tension in the string pulls taped pieces apart. White glue will work, but the drying time for white glue is prohibitive in a 45-minute class session.

Could we handle hot glue?

STEM Challenge- Build a suspension bridge! Check this post for the details.

Yes! And I can proudly say I thought of everything with the rules of this one. We had hot glue rules! We also had rules for how to make holes in the cardboard.

I bought low temperature glue guns and we used wide craft sticks. Students had to mark the spots on cardboard for the holes (the strings went through those holes) and I made the holes with my tools.

TIP: These need a good base to place the bridge on- we used stiff poster board one year and foam board another year.

The Ultimate Bridge

This bridge is the best invention ever! Straws and tape.

Two rules- it has to span a 12-inch gap and it has to look like a real bridge. (If you think the “real bridge” comment is silly, go back and look at the very first photo. That bridge was a mess.) The gap is across two lab tables that are 12 inches apart. This is an excellent way to create the roadway. The bridge has to be sturdy because the floor is too far away to make support columns!

STEM Challenge- Build a bridge that will span a 12-inch gap and hold weight. Check this post for the details.

Here’s what I did for this one- I gave the students a handout that had drawings of real bridges. The teams chose the model they wanted to build and then determined a way to use straws and tape. Just look at that one in the photo! Awesome!!

Alright, folks, I hope you learned a few things not to do when building bridges! Click on any of the images to see them in my store! And follow me- did you know you will get an email anytime I add something new to my resources? Yep!