Determine ultimate moment of resistance of doubly reinforced rectangular section of size 300 x 550 mm (effective) having tension reinforcement of 6 bars of 25 mm ${\phi}$ and compression reinforcement of 3 bars of 20 mm ${\phi}$. Use $M_{20}$ concrete, $F_{e415}$ steel and L.S.M.

Assume 50 mm effective cover to the compression reinforcement.

$b = 300 mm \\ D = 550 mm \\ d = 50 mm \\ To \ find \ M_u =?$

$Ast$ = $6-25mm \\ =6{\times}491=2946 \ mm^2$

$Asc=3-20mm{\phi}=3{\times}3.14=942mm^2 \\ f_ck=20N/mm^2 \\f_y=415N/mm^2 \\ \frac{d_c}{d}=\frac{50}{550}=0.09$