Method of Joints | Analysis of Simple Trusses Method of Joints
The free-body diagram of any joint is a concurrent force system
in which the summation of moment will be of no help. Recall that
only two equilibrium equations can be written This means that to
solve completely for the forces acting on a joint, we must
select a joint with no more than two unknown forces involved.
This can be started by selecting a joint acted on by only two
members. We can assume any unknown member to be either tension
or compression. If negative value is obtained, this means that
the force is opposite in action to that of the assumed
direction. Once the forces in one joint are determined, their
effects on adjacent joints are known. We then continue solving
on successive joints until all members have been found.