A three dimensional 2-node frame element ( XFRAME ) can be used for the linear dynamic analysis of 3-D framed structures. Nonlinear straight 2  n-node beam elements ( XBEAM2Q) are based on the thin walled Vlasov beam theory and include transverse shear deformation. The elements are capable of representing any open and closed sections.

The beam and shell elements can share the same nodes in stiffened shell structures or use the eccentricity effects with offset option. The seventh degree of freedom, the warping distortion of the beam is included at the nodes where the beam is presented. The material inelasticity is based on the elasto-plastic multi-layer techniques and uses the von Mises yield criteria.

< Fig. 11 2-nodes beam element >

Example Lee's frame in the following Fig. 12 is a good example of unattainable response using beam element. A Large displacement of elastic and elasto-plastic analyses of Lee's frame are carried out to validate the nonlinear performance. It shows good postbuckling behaviour.

< Fig 12.3 Deformed shape of at limit points >