In the field of engineering mechanics, a zero force member is a member (a single truss segment) in a truss which, given a specific load, is at rest: neither in tension, nor in compression.
In a truss, a zero-force member is often found at pins (any connections within the truss) where no external load is applied, and three or fewer truss members meet.
Basic zero-force members can be identified by analyzing the forces acting on an individual pin in a physical system.
If the pin has an external force or moment applied to it, then all of the members attached to that pin are not zero-force members unless the external force acts in a manner that fulfills one of the rules:[1] Restated for clarity, when there are no external loads at a pin joint, the two rules that determine zero-force members are:[2] It is a common practice to eliminate zero force members from a truss to simplify analysis.
Although an absolute minimalist design might eliminate all zero force elements from a truss, there are still sound reasons to retain some of these components in actual built systems: