Method of Joints: Struggling to Understand?

[Satoy]

I am struggleing here. Can anyone explain this concept to me? I don't understand how to first find the forces the supports exort and even if I did I don't know I I could proceed. Does anyone know a website that has a non-symetrical triangle that I can re-learn the basics off of. Or if some one on here could explain it to me that would be great.

Thanks

 

[Satoy]

never mind I found a website before I even got one view...thanks anyways

 

[Cyrus]

The only point to the method of joints is that the sum of all forces at ANY joint MUST equal to zero. In addition, all the memebers of the structure are two force memebers, and any forces that act on the structure MUST act on a JOINT. This makes good practical sense when you think about it too. If a member were NOT a two force memeber, then there would be a torque as well. And since there are no external torques to cancel out this natrual torque, the member would have rotation. So the ONLY force can be a two force, which means the forces are in the direction of the structual members.
When you do the method of joints, you start from whichever joint you can solve for all the unkowns, and then you work your way to the next joint, once you have figured out the forces in some of the members, until you find whatever force you were asked to find. (Sometimes it is necessary to look at the entire structure first to find the reaction forces so that you can first find a joint to work with though!).
I hope that helps.