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Bridge Building Project

Instructor: Amanda Robb
The goal of this project is to apply concepts in physics to build a bridge that holds the most weight. At the end of this project, you will understand basics in engineering bridges and create your own bridge.

Introduction

Goal: To build a bridge from 200 popsicle sticks and craft glue that will hold at least 20 pounds
Age: Middle school and up
Time to complete: Two days or more
Safety concerns: Don't stand under the bridge while you test the weight! It could break and fall on your feet.

Have you ever thought about how a bridge stays standing? Enormous bridges like the 26.4 mile bridge spanning Jiaozhou Bay in China support thousands of cars and trucks each day. One trailer truck alone can weight 80,000 pounds! So how do engineers make this work?

The answer depends on the purpose of your bridge. Short distances, like across a creek or stream, can be spanned with a beam bridge, a simple bridge with a straight deck and two pillars, or abutments, on either end. These bridges are easy and cheap to build, but they aren't good for long distances and their weight will eventually cause them to collapse.

Beam bridges are the simplest type of bridge
beam bridge

To solve this problem, engineers have created other types of bridges. Reinforcing the beam bridge with diagonal beams in a truss bridge can extend the distance and load a beam bridge can hold. The diagonal reinforcement beams are referred to as a truss, thus the name truss bridge.

Truss bridges use diagonal beams to reinforce the bridge
truss bridge

Suspension and cable-stayed bridges can span even farther, using cables anchored to abutments or into the bedrock on either side of the bridge to support the weight.

The Golden Gate Bridge in San Francisco is a suspension bridge
suspension bridge

Today, we're going to make a bridge of our own using popsicle sticks and craft glue. In real life, there are always constraints in engineering based on the budget, where the bridge is located and how much weight it must hold. Your budget is 200 popsicle sticks and one bottle of craft glue, and your bridge must hold at least 20 pounds (about the weight of a car tire) and span two feet in length.

Materials

  • 200 popsicle sticks
  • One bottle craft glue
  • Four or more binder clips
  • Newspaper to protect your surface from the glue
  • Six feet of string if designing a suspension bridge
  • 20 pounds of weight (you can use household objects, like cans, that equal 20 pounds, or two, ten pound athletic weights)
  • One ruler

Steps

1. First, decide which type of bridge you want to build. Beam bridges are easy to assemble, but don't hold a lot of weight. However, they can be supported with trusses. Suspension bridges are harder to make, but will support more weight. Only you can decide which bridge will be best!

2. Make a sketch of your bridge and get ready to build. You'll want to start building near where you want to test your bridge, so you don't have to carry it.

3. Assemble your bridge using the popsicle sticks and craft glue, making sure to work on the newspaper to protect your table. As you glue, you can use the binder clips to hold the popsicle sticks together as the glue dries.

Safety Tip!! Make sure the area under your bridge is free of hands, feet and other body parts when you test it. It might break!

4. Now, start applying your weight to the bridge and watch what happens.

Troubleshooting

If you're stuck on where to start, consider building your deck first. Then you can add your structural supports, like abutments, trusses, or suspension cables.

If you test your bridge and it keeps breaking, don't despair! A beam bridge is the weakest type of bridge, so try adding some additional support like trusses or cables.

Suspension bridges work because the cables are firmly anchored in the bedrock on the ends of the bridge. Did you anchor your cables to something solid on either end?

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