Forces operating on frame can cause three types of internal forces like bending moment, axial force and shear force. Therefore, it is possible to view frame member as combination of truss and beam member.
In a simple term, virtual work method can be defined as “Completed External work is identical to completed internal work”.
In frames, axial deformation is generally small corresponding to bending deformation and it is normal to disregard axial deformations. In this video, all the prospective deformations are considered.
Virtual Work facilitates to work out determinate and indeterminate structures as well as estimate their deflections. Therefore, it can obtain everything that all the other methods can attain collectively.