Deck truss or through truss: which is better for a balsa bridge?
What the two terms mean, how the roadway position changes bracing and clearance, and how your contest's rules usually decide.
Updated · 1 min read
Short answer: neither is better in general. The rules, usually the clear space and the load position, decide. A deck truss has the road on top of the truss. A through truss has the road between the sides.
The two layouts
- Deck truss: the roadway or loading surface is on the top. The truss is below it. Bracing between the trusses is simple, and nothing is above the road.
- Through truss: the roadway is at the bottom, and the truss rises on both sides above it. The top is open, or braced across the top if there is clearance. A vehicle or rod passes through the middle.
How to decide
- Check the clear space the rules require. If a car, a rod or a loading plate must pass through, a through layout may be needed.
- Check where the load attaches. A hook below the deck suits a bottom-chord roadway. A platform on top suits a deck.
- Think about stability. A through truss with no top bracing can lean sideways. See why bridges fail.
- Compare heights. Rules may set a maximum height, which limits how deep the truss can be.
Draw both against the rules before you commit. See truss basics.