In Hibbeler's book, Engineering Mechanics: Statics, on pages 264-265 it is mentioned that two assumptions are made in the design of a truss:
- All loadings are applied at the joints
- The members are joined together by smooth pins
Hibbeler goes on to say that because of these two assumptions, each truss member will act as a two-force member, and therefore the force acting at each end of the member will be directed along the axis of the member.
But why do these two assumptions lead to this conclusion?