The paper includes the following models for nonlinear structural analysis purpose: (1) uniaxial spring mode (or one-component model);(2) multi-axial spring model (MS model). Moment-curvature relation model considers distributed nonlinearity as well. By specifying the relation of moment and curvature at critical sections, it is not a discretized-section but similar to the uniaxial model in including no interaction among bending and axial tension/compression. This paper describes the models and presents the related formula.