Discretization of the basic-shape areas is described in the paper. Using Multi-axial spring model (called MS model) or fiber model for structural member idealization, the critical sections of the member are discretized in to a number of small elements (represented by springs or fibers) according to the section properties and materials (steel and/or concrete) properties.

For single material element, the same material element is comprised of Relatively Non-Disturbed(RND) state and Relatively Complete Disturbed (RCD)state is considered. The ratio of the two kinds of state changes with the loading level. The affection of the interaction between RND state and RCD state to the apparent behavior of 0 F is considered in the analysis of equilibrium equations. The key point of the method is that the response of RND state and RCD state can be defined by the apparent behavior of same material element. But the theory of duality disturbance can also be applied to the material element that is comprised of two(or more than two) kind of materials. [3-5]