$1.$ Fig. $2-$D$29$ rebar is placed. For beam section of $1,($fck$=28$MPa, fy$=500$MPa$)($D$29$ Nominal cross$-$sectional area$=642\mathrm{.}4$mm$^2,$ D$35956\mathrm{.}6$mm$^2)$

$1)$ Calculate the neutral axis of the cross section for the following three cases, indicate the positions of the three values on the cross section, and observe the change in the neutral axis.

$-$ For non$-$cracked sections

$-$ In case of concrete strain Ec$=$Ecu on the compression side

$2)$ Calculate the strain of the reinforcing bar in each case of $1)$ and compare the size by expressing it as a ratio to the strain of the reinforcing bar in the case of a non$-$cracked cross section.

$3)$ What must be the cross$-$sectional area of the lower rebar for this section to fail in equilibrium?

$4)$ What are the nominal bending strength and design bending strength?

$5)$ In the picture, $2-$D$35$ was placed instead of $2-$D$29.$ What is the design flexural strength of this beam?

$6)$ What is the minimum cross$-$sectional area of the tension rebar in this cross section?