Why bridges are made of triangles: a square folds, a triangle cannot
30seconds
A square made of four pinned rods folds flat at the slightest push, but a triangle of three rods cannot change shape at all. That one fact is why bridges, cranes and roof frames are built from triangles.
Drag the joints of a rod frame, add and remove rods, and watch a live count of how many rods a shape needs to stay rigid (2 × joints − 3). Then chain triangles into a Warren truss and try to fold it.
Deep dive · 3 min
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