Question

The distance between elastic neutral axis and plastic neutral axis for the cross-section as shown in figure below is ______.

Answer 1

Elastic NA is the CG axis.

Let elastic NA is located at a distance $y_c$ from top.

${\overline{y}}_c=\frac{150\times 30\times 15+150\times 20\times 105}{150\times 30+150\times 20}=51\text{mm}$

Plastic NA is equal area axis and let plastic NA is located at a distance $y_p$ from top.

Assuming plastic NA lies in flange.
$\frac{A}{2}=150\times y_p$
$\Rightarrow \frac{150\times 30+150\times 20}{2}=150\times y_p$

$y_p=25\text{mm}<30\text{mm}$
Thus plastic NA lies in flange.

The difference between elastic neutral axis and plastic neutral axis for the given cross-section is
$\Rightarrow 51-25=26\text{mm}$