Why Triangles in Bridge Design?

This is because triangles are resistant to forces from any direction and are not easily deformed.

A square, for example, would

Photo: Creative Commons 0

It is easy to deform like this.

However, if we add a diagonal bar to this rectangle, it becomes less deformable.

Photo: Creative Commons 0

And this figure is a combination of two triangles, right?

Triangles are strong against forces from any direction.

Photo: Creative Commons 0

Therefore, triangular shapes can be found on large bridges across wide rivers and straits.

Please look for them.

Photo: Creative Commons 0