# 3D Printing Truss Bridges

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This project has been adapted from STEAM trax, a division of Polar 3D, and is intended for use with 7-8 graders in a classroom setting.

Bridge design is a beautiful combination of math, engineering, design and architecture! In this instructable, you will be learning about a specific kind of bridge — the Truss Bridge. You and your group will work collaboratively to create a model truss bridge that spans two objects in your classroom and then pit your bridge against other teams in a head-to-head competition to see whose can hold the most weight.

This project focuses on a specific kind of bridge ― the truss bridge ― often used for fairly short spans carrying heavy loads like trains. The truss bridge represents a unique structural solution that combines simplicity of design and economy of material in a way that prior bridge designs did not. Before we explore the truss bridge, let’s take a look at other types of bridge to see how engineers use basic geometric principles to span distances — large and small — with bridges.

DURING THIS PROJECT-BASED LEARNING ACTIVITY, STUDENTS WILL BE LEARNING ABOUT:

• Structural engineering
• Geometric design
• 3D Printing
• Collaboration
• Documentation

### Supplies:

• Computer with internet access
• 3D Printer
• Skewers or other material to connect components
• Scisors
• Masses (Optional)

### Teacher Notes

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## Step 1: Design of Truss Bridge

During the Design & Explore section of your project, students will be challenged to create a Proof-of-Concept (POC) Prototype for your Truss Bridge. All of the 3D printing files and instructions you will need to complete your proof-of-concept model are housed here! Step-by-step BlocksCAD instructions are provided for each component to help you learn the basic functions you will need to design your own bridge in the design phases of your project. Once you have successfully used the instructions, you can make changes to an existing design or make a new design from scratch!

TRUSS BRIDGE DESIGN
There is one main component to the Truss Bridge proof-of-concept model. It can be downloaded below, in STL format. For users who will be creating their own components, step-by-step instructions are included for every part.

This is the main joint that will hold together the various struts and form the Truss bridge. Instructions for the design of this piece are also included so students can deign their own file.

For the example shown 14 connectors will need to be printed. The size of this connector may have to be changed depending on the size of the skewer that is being used.

## Step 2: Cutting Skewers

Once the bridge connectors have printed it is time to begin construction of the bridge!

Using scissors or a razor blade cut the skewers. Cut 19 pieces of skewer at 4 inches and 10 pieces at 5 and 7/8 inches.

## Step 3: Beginning Construction of Bridge

Once the skewers have been cut to the correct length begin assembling them with the connectors into a triangular pattern as seen in photos above. Make sure all connections are snug and that the skewers have been cut to the appropriate length.

## Step 4: Finishing the Truss

Continue the Triangular pattern until one half of the bridge is completed as seen in the photo above. If desired the bridge may be made larger than the example by simply adding more skewers and connectors. Once the first half is done simply repeat the process to produce the second half

## Step 5: Completing the Bridge

Once both halves have been constructed it is time to put together the bridge!

Add seven sections of 4 inch skewers to one side of the bridge then combine the two halves together to finish construction. Ensure that all skewers are firmly in place and that the overall structure is sturdy.

## Step 6: Testing and Evaluation of Bridges

Once students have designed and assembled their bridges it's time to test them!

Students should set up their bridge across a span or gap. Gradually apply weights until the bridge collapses. Record the largest amount of weight that your bridge was able to withstand.

After Testing their bridge students should be asked questions such as

• Why did your bridge fail where it did?
• What was restricting your bridge from holding more weight?
• How could the design of your bridge be improved?

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