Cardstock paper bridge competition

In my physics classes at Menlo-Atherton High School, we used a homemade bridge breaker to test the strength of student bridges. Students created bridges out of manila folder paper and hot glue. Maximum height are provided, and the distance between the two landing is specified, but in the end the winners are the groups that can create the best load-to-mass ratio.

Supplies

Manila folders
Hot glue and hot glue guns
Square metal rods
Scissors and/or razor knives

First step: Build a simple truss bridge to develop building skills

After an introduction to tension and compression in bridge members, students develop their construction skills building a simple, single truss bridge.

Long PowerPoint slideshow with introduction to compress and tension, and all sorts of images of bridges, feel free to make a copy and delete the slides you don’t need.
A PowerPoint slideshow with instructions can be found here.
PDF of blueprint can be found here.

Building the competition model

Students now build a bridge to meet the specifications. Suggested specs include:

Length (strongest portions at end of bridge must rest on the wood blocks on the force plates).
Width (determined by the width of your blocks on the force plates).
Maximum height (not required, especially if you measure load/mass).
Number of manila folders.
- We actually pre-cut the folders into a standard width using an electric paper cutter than can cut up to a ream of paper; cutting by hand works, but takes time and is prone to errors in width. Some students may want to cut using a razor knife and a metal straight edge.
Number of hot glue sticks (again, optional, but check your budget to see how many you can afford.

Load testing apparatus

We used two Vernier force plates resting on a platform with a rope and spring below it to apply tension to the center ‘saddle’ in the bridge. The force plates allow students to see a capture of the increasing force being applied, as well as the final breaking load (see screenshot in photo gallery below).

The photos below show the device. I don’t have blueprints for it, but the important components are described in the labels on the photos.

Resources

Sample scoring rubric can be found here.
You’ll have lots of bridges in your room for a few days. We used brown paper shopping bags for students to keep their materials together between days, and each class had a location in the class to store their bags (here are signs I used to identify class locations).