The best balsa wood bridge designs

Written by susan macdowell
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The best balsa wood bridge designs
Selecting the right glue is an important consideration in your balsa bridge design. (NA/ Images)

Whether you are designing your balsa bridge for a classroom project, a scout activity or as a team member for a local, regional or even national balsa bridge competition, the best balsa wood bridge designs will all include the same components. First, your bridge must be designed to meet the problem's specifications. Next, you need to use high-quality balsa wood and glue that provides a good joint. Finally, all components of the bridge need to be straight and level.

There is no single best balsa bridge design, as each competition has different specifications, but the best bridges designs share some similar components. They satisfy the specific bridge problem's requirements, carefully consider dimensions, are one solid structure and incorporate trusses for additional strength and stability.

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Meet the Problem's Specifications

Balsa bridge design competitions require a set of specifications that must be met. These may include the maximum or minimum weight of the structure, if a specific size or shape of balsa wood must be used, the types of glues permitted, whether anything other than wood or glue can be added and the maximum or minimum dimensions of all aspects of the bridge. Make sure you understand these specifications so that you can ensure your design meets all the requirements.


Every balsa bridge problem will provide a range of acceptable dimensions. The builder may be given a choice of having a bridge with a height of 2 to 4 inches, and a span of 10 to 12 inches, for example. In all cases, using the smaller dimension for both the height and the span will create a bridge design that holds the most weight. The closer to the ground your bridge sits, and the shorter the span, the stronger your bridge design will be.

One Solid Structure

All components of a balsa bridge should be securely fastened to each other with glue, if permitted, or with pegs, pins or interlocking components, if the problem specifications do not permit glue. A bridge designed as one solid structure will not be subject to dynamic moment, which can lead to structural instability when load is applied. It will hold more weight as a result.

Truss Design

Triangular units of balsa can be used to create a truss bridge. The diagonals in the trusses spread the loads, reducing the force of compression on the load-bearing members of the bridge. Including trusses in the bridge design enables a balsa bridge to bear more weight than a bridge made solely of vertical members. Trusses can be included to reinforce the span, as well as to increase the load-bearing ability of the columns supporting the bridge deck.

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