1, when using the elastic theory to calculate the load, it is assumed that the structure only undergoes elastic deformation under the load, and the effects of the load are directly superimposed, and the influence of the load on the structure is linear. At this time, the load calculation diagram is usually a straight line, curve, etc.

2. When the load is calculated by plastic theory, the structure may not only undergo elastic deformation, but also undergo plastic deformation to a certain extent, and the influence of the load on the structure is nonlinear. At this time, the load calculation diagram is usually a curve, parabola, etc. , showing obvious nonlinear characteristics.