"Method of Joints" for truss structures in statics?

Question

1. Is there any rule about the first joint to start with when adopting this method? Does it matter which joint is evaluated first? Please explain...

2. Is the method below the correct way to approach questions when using the "method of joints"?

- First take the moment about a joint/point (usually about a point which is connected to the external environment) and let it equal 0.

- Next take the sum of all external forces in both the x and y direction and let them be 0 and solve for the forces caused by the external environment.

- Then start working on a joint to find the forces in the members of the truss.

NOTE: When i say "the forces caused by the external environment" i mean the forces by the places where the truss is connected to the earth, like at pin connected joints & roller joints etc.

Answer 1

no there is no any rule to start with the first point while analyzing the truss by method of joints.as in case of joints where three members meet, two being horizontal and one vertical forming a right angle, the axial force at the vertical member is directly equal to zero provided that no external forces(may be vertical or inclined) are acted directly upon or below it.  but ,generally, first  the reaction due to the external forces are found out before start finding the internal forces(axial forces).

yes the method u described is correct but as i said in case of three members meeting about u can directly say the vertical member has zero force. these members are  called zero members i guess. and in some the problems its easier to start calculating thru these zero memeber and finally end at the joint which is connectd to the earth. this help u save time from determining the external forces at the begining.wat i mean to say is the forces due caused by external environment can also be determind by starting from zero member.