Balsa Bridge Building

Bridges- Balsa Wood

Here below is a rough outline of steps in which you have to follow to make a truss bridge.

Step 1: Complete truss design and sketch ideas.

Step 2: Complete a three-view sketch (top, side, and end) of the bridge you plan to build.

Step 3: Build the model truss bridge you designed.

Step 4: Test the model truss bridge you designed.

Safety

Be safe when using an Exact-o knife, avoid cutting yourself

Don’t touch your eyes when using glue

Objectives

Understand how a bridge works with tension and compression

To know what it takes to build a sturdy bridge

Building a truss bridge

To effectively design a truss bridge, several of the fundamental systems used by engineers will be taken after. The first step in which you have to take is to sketch designs, that follows the basic structure of a truss bridge. By creating a model, you are able to test the design and determine its stability.

By determining the stability of your model that your bridge holds, you are able to find the failure mass. The efficiency of your bridge can be found by dividing the failure mass by the mass of your bridge in grams. The formula looks like this:

Efficiency = Failure Mass (g)/Mass of Structure (g)

Step 1: Sketching ideas

Sketching helps engineers build up on different designs. Through this engineers are able to narrow down their choices and carefully plan on which design is better.

Below is a miniature design in which you can use as a reference. You can change up the design and add other structures so to make it more stable.

Step 2: Draw a three-view sketch

Now that you’ve decided on a design, the next step is to make a three-view sketch of your chosen design. To make a three-view sketch of your design, draw the top, side, & end view of your design. Don’t forget to draw your design to full scale for this is how you’re going to assemble your bridge. Look to the picture below for reference.

Step 3: Build the model

The materials needed to build the bridge are listed below

• Balsa wood or basswood strips

• Tweezer set (optional)

• Hobby knife or Pitsco Timber Cutter

• Pitsco Construction Caddy II (optional)

• Structure-Building Pins or T-pins

• Pitsco Accu-Fixtures Set (optional)

• Three-view sketch or drawing (full scale)

• Pitsco Timber Tester (optional)

• Waxed paper (12" x 18")

• Pitsco Lil’ Termite Sander (optional)

• Masking tape

• Foam board (minimum 12" x 18")

• Pitsco Colored Structures Glue or HD Bond II

• Square

• Ruler or scale

• Small clamping devices such as Bridge

Construction Clips or clothespins (optional)

(Tips)

Different types of joint to keep in mind when you are constructing the bridge.

Step 4: After the bridge has been fully built and can support itself, it’s time to put it up to the test. Make sure your bridge is placed evenly on the bridge tester and have the hanging mass in the middle, so the weight can be disputed evenly throughout the bridge. Slowly add weighs, around 1kg every couple seconds or so, to make sure the bridge doesn’t take a large amount of force in a short time. After the bridge breaks, answer the following questions.

1. How much weight did the bridge hold?

2. If you were to change something about the bridge to make it more efficient, what would it be? Why?

3. Why do you think suspension bridges can hold tons? Which law of physics do you think supports this idea?