...
Frame objects, used to model beams, columns, braces, and truss elements in planar and 3D systems, are straight lines which connect two nodes. Biaxial bending, torsion, axial deformation, and biaxial shear are all accounted for in the beam-column formulation (Bathe and Wilson, 1976) which characterizes frame behavior. Material nonlinearity may be modeled through the assignment of frame hinges. Multiple straight segments may be used to model curved members, and features are available for non-prismatic members. The CSI Analysis Reference Manual (Chapter VII: The Frame Element, page 89) provides additional information on frame objects.
...