How do you identify zero-force members in a truss?

Zero-force members carry no load under a given loading condition. They can be identified using two rules: (1) at a joint with only two non-collinear members and no external load, both members are zero-force; (2) at a joint with three members where two are collinear and no external load acts along the third member, that third member is zero-force. These members provide stability and may carry load under different conditions.