Truss Analysis - Sections Method

[aaronfue]

I was analyzing a truss and when I checked my answer there was a "new" point where the moment was taken about that was not in the original diagram. After reading the text I could not find anything that stated why, when, or how to do this? I've attached the image of the answer.

Can I figure out the forces without creating this alternate point? If I were to create an additional point, how would I know what lengths to use?

 

[Mech_Engineer]

I'm sure it was probably described in the original problem statement. My guess is it's a hypothetical modification- if these extra trusses are added how does it effect the forces, etc.

 

[Studiot]

Hello aaronfue.

You can take moments about any point or line you like.
The moment of any force is given by the force time perp distance as usual.

Obviously if the line of action of a force passes through a point its moment is zero about that point.

So when analysing mechanisms or structures taking moments about such points eliminates forces from the equation.

In your case F_bc, F_hg, A_x, all pass through O.

This leaves an easily soluble moment equation with a single unknown.

Cool or what?



As to the distances well that's a matter of geometry.