## Plastic Neutral Axis

Obviously at all stages of loading, the compression force (FC) induced by the applied moment must equal the tension force (FT). This being so, then at the formation of the plastic hinge where all the material is subjected to the same stress i.e. py, the plastic neutral axis must be that axis which equally divides the area into two separate parts, i.e.

Fi— Compression Force — (Ac * py) Tens ion Force — (A j x py)

where

Ac = Area in compression, Ay = Area in tension Py - yield slress and Force in compression=Force in tension i.e. Area in compression=Area in tension

In plastic analysis the neutral axis is the equal area axis.

2.3.3 Evaluation of Plastic Moment of Resistance (M^) and Plastic Section Modulus

In elastic analysis the limiting elastic moment can be expressed in terms of the yield stress and the elastic section modulus, at the limit of elasticity;

Similarly in plastic analysis, the plastic moment of resistance can be expressed in terms of the yield stress and the plastic section modulus.

Consider the section shown in Figure 2.42.

Consider the section shown in Figure 2.42.

Figure 2.42

Cross-section

### Figure 2.42

If the rectangular section is subjected to a moment equal to the plastic moment of resistance Mp of the section then we can determine a value for the plastic section modulus.

Hence for a rectangular section the Plastic Section Modulus

The Plastic Section Modulus £o=1st moment of area about the equal area axis

+1 0

### Responses

• Sheshy
What is plastic neutral axis?
2 months ago