What is the best truss design for a balsa bridge?
Warren, Pratt, Howe or something else? Why no truss wins everywhere, and how the span, load point and clear-space rule choose for you.
Updated · 1 min read
Short answer: there is no single best truss. A Warren truss (zigzag diagonals) or a Pratt truss (verticals plus diagonals) is a good starting point for most contests. The best one for you depends on your span, where the load is applied and the clear space your rulebook requires.
How to choose
- Start from the rules. The clear-space requirement and the load position often rule out some shapes. Check them first.
- Prefer fewer, shorter compression members. Sticks being squeezed fail by buckling, so a shape that keeps them short wins. See truss basics.
- Keep joints simple. Every joint you add is a place for the bridge to fail and glue to add weight. A design with fewer joints that you cut well beats a clever one you cut badly. See cutting joints by hand.
- Match the load path. The load should reach the supports through straight paths, with no bending in the sticks.
- Build a quick model and break it. What bows and what opens first tells you more than any chart.
Common starting shapes
- Warren: simple, light, few joints.
- Pratt: under a downward load, the diagonals are pulled, so the long members are in tension.
- Howe: the mirror of Pratt, with the diagonals pushed.
Our contest pages put each contest's rules in plain words, which is the first step to picking a shape that is legal.