How Do Moments and Lines of Action Relate to Equilibrium?

[qazxsw11111]

Ok, so for equilibrium (no moment about any point), all the lines of action must pass through a single point right? But what about a plank, balanced at its centre, with forces on both sides of the plank so the forces are in equilibrium, and there is no moments also. But what about the line of action meet at a point thing? This confuses me lol.

 

[Doc Al]

Ok, so for equilibrium (no moment about any point), all the lines of action must pass through a single point right?

Not necessarily. A special case is when the three forces are coplanar and parallel, which applies to your plank example.