Warren, Pratt and Howe trusses: what's the difference?
How the three common truss layouts differ in the direction of their diagonals, which members are pushed or pulled, and which suits a balsa bridge.
Updated · 1 min read
Short answer: all three are triangulated frames. They differ in how the diagonals are arranged, which changes whether each diagonal is pushed or pulled.
| Truss | Layout | Under a downward load |
|---|---|---|
| Warren | Diagonals zigzag, with no verticals (or few) | Diagonals alternate between push and pull |
| Pratt | Verticals plus diagonals sloping down toward the middle | Diagonals are pulled, verticals pushed |
| Howe | Verticals plus diagonals sloping up toward the middle | Diagonals are pushed, verticals pulled |
Which to choose?
- Warren has the fewest members and joints. It is simple and light, and a common starting point.
- Pratt keeps the long diagonals in tension, so the pushed members are the short verticals. That works well for slender balsa sticks, where long pushed members buckle.
- Howe puts long diagonals in compression, which makes buckling more of a concern for balsa.
For other loads or load positions the pattern can change, so check which members are pushed in your own design. See which members are pushed or pulled and truss basics.
The rules, especially the clear space and the load position, matter more than the name. See the best truss design.