# How to Build a Suspension Bridge Model

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

In this project, you'll be creating a suspension bridge. Through building this model, you'll understand the principles of force distribution and how engineers use cables to accomplish this in suspension bridges.

## Introduction

 Goal: To create a model suspension bridge Age: Middle school and up Safety concerns: None Time: 3 days

Picture a standard beam bridge, one with large columns underneath to support it and a flat roadway. The bridge might seem solid as cars and trucks pass over it daily, but now picture that bridge in the middle of an earthquake. The sturdy supports attached to the ground are now torn apart, shredding the bridge.

In areas that have frequent earthquakes, like California, this presents a problem for bridge engineers. One type of bridge that withstands earthquakes well is a suspension bridge, or a bridge supported by a cable system. The cables are anchored to the land on either side of the bridge and towers in the middle.

Since the bridge is supported mainly by a cable system, it remains flexible while the earth shakes. Even though the bridge might twist and shake during an earthquake, it should return to a useable condition once the tremors stop. Today, you'll learn how to make your own suspension bridge using popsicle sticks, glue and string.

## Materials

• 200 popsicle sticks or more, depending on how big you want your bridge to be
• 6 ft of string, again depending on how large your bridge is and how many cables you want to use
• 1 bottle craft glue
• Scale, if you'd like to know exactly how much weight your bridge supports

## Steps

1. First, you'll want to construct the deck, the flat part that people and cars move across. You can glue the sticks vertically, horizontally, or even stack them. It's up to you to make the strongest deck. Make the deck about 2'' longer than you want it to span.

2. When your deck is fully dry (this may take overnight), you can start to build the towers, which connect to the deck and will hold the cables. You'll need at least two towers, but you can add more. Again, its your choice how to design the towers, but a few popsicle sticks glued together vertically works well. Once your towers are built, glue them to the deck securely.

3. Once that structure is done, it's time to add the main cables. Anchor the cables firmly to one side of the bridge. You can wrap them underneath and secure them by tying them to the underside of the bridge, taping them, gluing them, or placing a heavy object on top of them. Attach the cables to the first tower, and then string them to the second tower, and then to the end of the bridge on the other side. Do this on both sides of the bridge.

4. Now, add suspender cables running from the main cables on the outside to the deck. You'll need to measure the distance between the top of the cables and the deck, then cut your string with an extra 2'' included. Now, tie one end of the string to the cable and anchor the other one to the deck by tying, taping or gluing it.

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