Trusses
Why a bridge is made of triangles and not of squares.
A triangle of bars pinned at the corners cannot change shape without a bar changing length. A square can: push one corner and it folds into a diamond. That is the whole reason every bridge, roof and crane is made of triangles.
In a truss, each bar is either pulled or pushed and nothing is bent, which is what makes it light: a bar is far stronger along its length than across it. The bars in tension and the bars in compression can be worked out corner by corner, and that is how bridges were designed before computers.
| What | What it means |
|---|---|
| Tension | the bar is being pulled and holds itself together |
| Compression | the bar is being pushed and may buckle |
| A pin joint | passes force but no turning |
The app's bridge is rods between pinned bodies. Give the rods a strength and load it until something goes: what breaks first is the answer.
Open the truss scene in the app to watch this one run.