Bar and truss finite elements are one-dimensional structural elements that carry axial force through nodal translational degrees of freedom.
How They Work
The local bar element assumes an axial displacement field along the element length. The strain is the derivative of that displacement, the stress follows from Hooke's law, and the local stiffness has the familiar axial form proportional to AE/L.
For truss analysis, local bar stiffness is transformed into the global coordinate system using direction cosines. Plane truss members use two translational degrees of freedom per node in the global plane, while space truss members extend the same transformation idea to three dimensions. After transformation, each member contributes to the global stiffness matrix through the Direct Stiffness Method.
Modeling Assumptions
The member carries axial tension or compression.
Shear force and bending moment are neglected.
Transverse displacement effects are ignored within the element formulation.
Pin-connected truss idealization is appropriate for the structure being modeled.
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