Traditional calculation technologies are based on substantial simplifications and do not allow for very important (and in certain cases - crucial) situations related to changes in the design model during the life cycle of a building. The objective of the study was to analyze the processes that lead to changes in the structural design scheme, and to determine general principles of modeling changes in the design model. The study determined a set of basic elementary operations that allow modeling a step change in the design model. The paper presents the analysis of building up the model, and emphasizes the necessity to modify original geometrical parameters of the design scheme elements. The paper formulates modeling principles, presents theoretical foundations and principles of the calculation technology which tracks phase changes of the stress-and-strain state allowing for changes in the design scheme. The article comes up with proposals to implement the computational analysis during the structural degradation for different reasons (wear, corrosion, micro-and macro-fracture under load etc.). The research results can be applied in the analysis of building systems, separate designs and test samples in order to allow adequately for changes in the design scheme.