Should I build a truss bridge or a beam bridge?
For most balsa bridge contests a truss is lighter for the same strength. When a simple beam still makes sense, and how to decide from the span and rules.
Updated · 1 min read
Short answer: for any span longer than a hand's width, a truss is usually lighter for the same strength. A solid beam bridge is easier to build but wastes wood.
Why a truss wins on weight
A beam bends. Under load, the top is squeezed and the bottom is stretched, and the middle of the beam does little work but still weighs the same. A truss puts wood only where the forces are, in straight sticks that are pushed or pulled. That is how it holds more load for the weight. See truss basics.
When a beam can make sense
- A very short span, where a truss has no room for its triangles.
- A contest that restricts the shape or demands a continuous deck.
- A first attempt, to learn gluing and testing before a harder build.
How to decide
- Check your rulebook for allowed shapes and the clear space.
- Estimate how many triangles fit in the span. Too few and a truss is not worth it.
- Build a quick model of each and test both.
See also the best truss design.