Objective
Construct and test a model bridge that supports the most weight possible.
Description
A structure is something that will support an object or weight and can be natural or man-made. A structure’s construction can be frame or shell. Structures, such as buildings and bridges, have many forces acting on them. These forces – pulling, pushing, bending, twisting, and shearing – must be taken into account by engineers as they research, design, plan, and construct such projects. A lot of problem solving occurs in the design and construction phases. Take bridges, for example. Bridges are designed to get people and their belongings across rivers, valleys, and so forth, and must withstand the forces (people, weight, wind, gravity) acting upon them. Bridges are also designed in three basic types – beam, arch, and suspension – each with its own advantage. One type of problem for engineers to solve is what type of shape to use, and that answer is generally the triangle as it offers the greatest strength.
In this activity, you study one aspect of structural engineering – bridge building. You become an engineer by designing and building a wood model truss bridge. You discover the importance of the truss in structural design and solve problems by designing, creating, and testing a model bridge.
Procedures
- Make several small sketches of possible design ideas for a truss bridge.
- Draw ideas of how the sides, top, and bottom (roadbed) of your bridge design will look.
- Decide on one that is acceptable. The design may include a combination of your design ideas.
- Develop your sketches into full-size drawings on graph paper.
- Construct the model truss bridge using the Balsawood Bridge Kit.
- Use a small piece of tape in each corner to fasten each drawing to a piece of cardboard.
- Next, use a small piece of tape in each corner to fasten the waxed paper in position on top of each drawing.
- Cover each mounted drawing completely with the waxed paper to prevent the wood and glue from sticking to the drawing.
- Use a ruler and pencil to measure and mark the balsawood at the desired length.
- Lay a strip of balsawood on top of the line that represents the roadway (bottom piece) of the side view that you have drawn.
- Mark and cut this piece to match your drawing.
- Use two pins to fasten this piece of wood to the pattern attached to the cardboard.
- Lay another strip of balsawood on top of the line that represents the top piece of the side view that you have drawn.
- Mark and cut this piece to match your drawing.
- Use two pins to fasten this piece of wood to the pattern and cardboard.
- Carefully measure, cut, and glue the remaining structural pieces that make up the side view.
- Measure the angles carefully and pin each wood piece in place.
- When you finish construction of the first side section of the bridge, leave it attached to the cardboard and begin construction on the top section, as explained in the next step, using the same techniques as before.
- Continue the process of carefully measuring, cutting, and gluing the structural pieces that makeup the bridge’s top section.
- Measure the angles carefully and pin each wood piece in place on top of the waxed paper and pattern.
- Continue the process of carefully measuring, cutting, and gluing the structural pieces that makeup the bridge’s bottom (roadway).
- When you finish construction of the bottom section of the bridge, leave it attached to the cardboard and begin construction on the second side section, as explained in the next step, using the same techniques as before.
- Locate the cardboard/pattern with the completed side of your bridge.
- Carefully remove the pins that are securing the side section and lift it off of the waxed paper. Try not to damage the wood pieces as you remove the pins. It may help to slightly twist the pin as you remove it. You need this same pattern to construct the second side of your bridge.
- Carefully place the completed bridge side section in the storage area so that it is not damaged.
- Continue the process of carefully measuring, cutting, and gluing the structural pieces that make up the second side.
- Measure the angles carefully and pin each wood piece in place on top of the waxed paper and pattern.
- After the four sections of your bridge are completed and the glue has dried, carefully remove the pins that are securing any remaining bridge sections attached to the cardboard.
- After all four bridge sections have been removed from the waxed paper, inspect each one for any loose joints, weak areas, or broken wood, and repair as needed.
- Trim away any excess glue from the bridge sections using the hobby knife.
- Test fit each section together for proper fit before gluing.
- Assemble all four sections together using glue to form your completed truss bridge.
- Use pins and clothespins to help hold the sections together while the glue dries.
- Carefully place the completed bridge in the storage area to dry.
Continuation
- Add cardboard to create a roadway to the bridge.
- Create a multimedia presentation to accompany the model.
- Paint the bridge for a finished look.