Truss Analysis: Method of Joints

[JordanIV]

I'm doing this truss analysis by method of joints and I have determined the forces at "A" and "G" and have moved on to determine the loads at each joint. I have determined the angle to be 63.34 for the 10' and 53.13 for the 15'(I took the inverse tangent of 20/10=63.34 and I took the inverse tangent of 20/15=53.13). As you can see I have calculated the forces at joint "A" and i then moved on the joint "L". For Joint "L", I feel that I have made a mistake somewhere and this may have made my other calculations wrong. I want to know if my calculations made at "L" are correct. Also, I believe that "AL" would actually be symmetrical to "KL", but am not sure of that. The truss is also in symmetry so the other side will just match up with the other side.

 

[Valkarie]

Your calculations for joint "L" appear to be correct. The forces in the truss are indeed symmetrical, so that AL = KL. That means that the forces at "L" will be equal in magnitude but opposite in direction. Thus, the force at "A" will be equal and opposite to the force at "K". The angle at "L" is the same as the angle at "A" (63.34°) since they are connecting the same two members.