Warren Truss Popsicle Stick Bridge

Hello there! In this informative step-by-step guide, I will take you through the procedure done by me and my team in order to develop an effective and cost efficient Popsicle stick bridge using a warren truss pattern. Whether you're reading this to pass some leisure time or are attempting to build a bridge of your own, I hope this guide leaves you very informed and that executing this project was as much fun for you as it was for me and my team!

Step 1: Organizing a Team

The first order of business for any team is to make sure everyone is assigned a part in the project. The following is how our team was organized (it includes roles and dates for each job to be done) :

Justification for bridge design (December 5th) : Andrea Castillo and Stella Bagno

Math for the bridge (December 5th): Juan Zapata

CAD sketches (December 11th): Juan Zapata and Thatcher Strand

Bridge building (December 17th): All members

Putting together the booklet (December 17th) : Kiara Vargas

Video production (December 20th): Oliver Perez

Narrating the video (December 19th): Thatcher Strand

Step 2: Why a Warren Truss Pattern?

The Warren Truss design has equilateral triangles in the framework to spread out any load of weight placed; loads on the diagonals alternate between compression and tension (approaching the center), with no vertical elements. While elements near the center must support both tension and compression in response to live loads. This configuration combines strength with resourcefulness of materials and can therefore be generally light and efficient. Because it spreads out the load equally throughout the bridge and it is relatively simple to build, my team and I chose the warren truss design to build in order to complete the project.

Step 3: The Math Behind the Reason

What's engineering without some math to back up our project? We took into account the math that goes into building our bridge. These are our findings:

We wanted to be putting 105 lb of force on our bridge, which translates to 467.063 Newtons. This means that if the weight is distributed evenly, every triangle will be receiving 38.9N of force, and the four corners touching the table will get 116.7N each. To find how much force of the 38.9 Newtons is going into each side of the triangle, we use tangent and cosine times the force in Newtons. To do this, the equilateral triangle must be divided in two, creating two right triangles, as demonstrated by the imaginary line.

To find the force going on the popsicle sticks on the bottom per triangle:

Since the new side is going straight down, like the force, we can use tangent to find the force applied on the opposite side of the angle.

Tan(30) = (x/38.9)

Multiplying the whole equation by 38.9 and solving gives us

38.9 tan(30) = 22.45N

Which is how much force half of the bottom popsicle stick is holding. Multiplying by 2 tell us that the popsicle sticks at the bottom are holding 44.90N per triangle, but this force is divided equally by the 3 popsicle sticks that are at the bottom of each triangle.

To find the force going on the popsicle sticks on the side of each triangle:

We can use cosine since we already know the force applied on the adjacent side of the angle and the goal is to find the force applied on the hypotenuse.

Cos(30) = (x/38.9)

Multiplying by 38.9 yields

38.9 cos(30) = 33.68N

Which is how much one side of a triangle is holding. Multiplying this by 2 reveals how much force is applied to both sides of the triangle, 67.38N.

In conclusion, each triangle will support 44.9N at the bottom and 67.38N at the sides.

After doing this math, my team and I were certain that the warren truss design was the best option.

Step 4: Does This Mean the Design Is Flawless?

Of course not, nothing is perfect! One particular weakness was taken into account. The bridge will most likely to fail at the circled locations shown in the picture above, since it is when the gap begins and will push against the table, acting as a lever where the force input in the middle of the bridge yields an output of about 2 times as much if the force is applied directly to the middle.

Step 5: Sketching Out a Plan

Before physically constructing the bridge, we decided to create computer generated sketches in order to have some blueprints and to see what was to be expected. The pictures above show the 4 sketches done.

Left picture: 3D sketch of the bridge

Top right picture:Front view sketch of the bridge

Middle right picture: Side view sketch of the bridge

Bottom right picture: Top view sketch of the bridge

Step 6: Materials

Now that a plan has been laid out, it's time to get building! The following is a list of materials needed to create the bridge:

.Popsicle sticks (Approximately 160 sticks)

.White liquid glue (1 bottle)

.A hot glue gun

.Glue sticks for a hot glue gun (numbers of sticks vary depending on the size of glue gun that will be used)

.Rulers (2 in order to measure a total of 24 inches/60 centimeters)

.Clothespins (At least 12)

.A pair of scissors

.A pen or pencil

Step 7: Building the Side of the Bridge

1. Begin with making 11 triangles. Take 3 Popsicle sticks and lay them out in a triangle shape. Attach an end of one side stick to an end of the bottom stick with hot glue (be sure to place the side stick at a 45 degree angle). Repeat this with the other side stick. The point where the two side sticks meet should not have the sticks overlapping, but rather side by side (This is shown circled in red on the top picture on the right). Repeat the entire step 10 more times.

2. Attach the triangles. Get two triangles and turn one upside down (One triangle should have the bottom stick facing down while the other should be facing up). Attach 1/3 of Popsicle stick with white glue on the middle of a triangle side where it will overlap with the other. Add hot glue on the Popsicle piece and the ends of that side and attach the other triangle. Add a clothespin to the part with white glue. Repeat this step until all triangles are attached.

3. Wait 30 minutes for white glue to dry; afterwards, remove clothespins.

4. Connect the top and bottom of the structure. Glue 1/3 pieces to the middle of the bottom stick (seen circled in blue in the picture on the top right) of each triangle with white glue. Glue down Popsicle sticks to connect the triangles together with white glue (specific alignments seen circled in red in the picture on the left). Secure the glued parts with clothespins.

5. Wait 30 minutes for white glue to dry; afterwards, remove clothespins.

6. Add reinforcements. Apply hot glue on points shown in the middle right and bottom right pictures. Your end product should look like the picture on the left.

7. Repeat steps 1-6 once more.

As an end result, you should end up 2 sides for your bridge.

Step 8: Attaching the Sides

1. Lay out the pattern (shown in the picture on the right). Stand both of the sides upright.

2. Connect the sides by gluing (using hot glue) the sticks following the pattern. A total of 19 sticks should be used.

3. Add reinforcements. Go back with the hot glue and apply some to all the points that had been glued done previously.

4. Once the glue is all dried up, flip the bridge upside down and repeat steps 2 and 3.

5. Wait for glue to dry.

Viola! Your bridge is now finished.