6.6 : Zero-Force Member

A truss is a framework that comprises slender members connected at their ends by joints. Trusses are widely used in engineering and architecture to stabilize and strengthen structures like bridges, roofs, and towers. Truss members are designed to carry loads through tension and compression, enabling the truss to withstand external forces.

One critical concept in truss design is the idea of zero-force members. It refers to a truss member that experiences no stress under loading conditions. During the analysis of a truss, certain members may have zero force, indicating that they do not contribute to the overall load-bearing capacity of the structure. Identifying zero-force members is essential for optimizing the design of truss structures.

There are two conditions for the existence of zero-force members. First, if only two non-collinear members form a truss joint, and no external load or support reaction is applied to a joint, both members must be zero-force members. Second, if three members form a truss joint, and two are collinear, the third member is a zero-force member, provided no external force or support reaction has a component that acts along that member.

Consider a truss with a roller and pin support and an external load at joint E. Here, joints H and G are three-member joints with two collinear members. Applying the second condition, EH and FG are zero-force members. Using the zero-force condition to the joint F,  DF is a zero-force member. However, due to the external load, ED cannot be a zero-force member.

Zero-force members are vital in maintaining truss stability and equilibrium, optimizing structural design, and reducing material and construction costs.