Why are bridge and roof trusses built from triangles?
A pinned triangle cannot change shape without changing a side's length, so it stays rigid.
- Triangles use the least steel of any shape
- Triangles are easier to paint
- A pinned triangle cannot change shape ✔
Why: A square with pinned corners folds into a diamond. A triangle with pinned corners can only deform if a member stretches or shortens. Planar trusses are built from triangular subunits for this reason.
Huh, didn't know that: Three-dimensional space trusses use the tetrahedron, a triangular pyramid, as their basic unit.
Why do engineers love triangles? Every other shape keeps folding under pressure.
References
Answer: A pinned triangle cannot change shape. A square with pinned corners folds into a diamond. A triangle with pinned corners can only deform if a member stretches or shortens. Planar trusses are built from triangular subunits for this reason.
- Engineering Statics (Baker and Haynes): 6.3 Trusses engineeringstatics.org/Chapter_06-trusses.html
Simple trusses are made of triangles, which makes them rigid when removed from supports.
Checked 2026-10-10. - Engineering Statics (Baker and Haynes): 6.3 Trusses engineeringstatics.org/Chapter_06-trusses.html
Planar trusses are two-dimensional trusses built out of triangular subunits, while space trusses are three-dimensional, and the basic unit is a tetrahedron.
Checked 2026-10-10.
Think this answer is wrong? Tap "Challenge this answer" on the card in the game and tell us why.
More stuff everyone should know
That's stuff everyone should know.