Yield Penetration Model
A yield penetration model is used to compute the yield penetration lengths at the end sections of an element as shown in Figure 2. Yield penetrations parameters ад and ав specify the portion of the element where the acting moment is greater than the corresponding yield moment of the section. For simplicity, a linear moment distribution is assumed even in the case of the presence of distributed loads. However one can subdivide each structural element into a number of elements in order to capture closely a parabolic variation.
As long as the current moment distribution is defined, a set of geometrical oriented rules is used in order to define both the yield penetration lengths and the stiffness of the central part of the element. The yield penetration parameters are checked with the previous maximum penetration lengths, while the plastic regions of the element are considered only to expand and not to contract.