The virtual distortion method (VDM) of truss analysis is extended to simulate structural modifications in rigidly jointed frames. An analytical formulation is derived for the displacements of the modified frame. The formulation is applicable to modifications of material distribution (change in moment of inertia of members), but can readily be extended to cover the changes in physical properties (e.g. generation of plastic zones) in a design or loading process.Two practical examples are given to show that the" exact response of the modified structure can be obtained efficiently from the results of the analysis of the original structure. The application of the developed formulation in iterative optimization procedures and its extension to elastic-plastic analysis are described. Finally, sensitivity related applications of VDM are discussed.