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Zero Force Members | How to Identify Zero Force Members in Trusses

What is Zero Force Members

zero-force member can be defined as a structural member (a single truss segment) in a truss structure that, when the load is applied to the structure, is at rest (no tension or compression forces). Zero force members are members in a truss/frame that theoretically have no force in them.

Zero Force Members Identifications

These members in trusses are typically found at pins where no external load is applied, and three or fewer truss members meet. Identification of basic zero force members can be made by analyzing the forces acting on an individual pin in a physical system.

When an external force or moment applied to the member, then it means the members attached to that member are not zero-force members unless the external force acts in a manner that fulfils one of the following conditions:

  • If two non-collinear members meet in an unloaded joint, both are zero-force members.
  • If three members meet in an unloaded joint of which two are collinear/parallel, then the third member is a zero-force member.

Reasons for Zero-Force Members in a Truss System

  • Zero force members contribute to the stability of the structure, by providing buckling prevention for long slender members under compressive forces
  • Zero force members can carry loads if variations are introduced in the normal external loading configuration

In summary for a truss joint with two non-collinear (not at the same line) members only with no external force.

Given that two collinear members, the third member, will be a zero force member. Identifying zero force members will save the time and effort required to analyze a given truss. Also, it will simplify the analysis by eliminating zero-force members.


How to Identify Zero Force Members in Trusses

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