Situation $5$: Design the smallest circular spirally

reinforced column having not more than $4\%$

reinforcement to carry an axial compression of

$P_D=1800kN$ and $P_L=1400kN.$ Use $f_c^{\text{'}}=$

$25$MPa and $f_y=400$MPa.

What is the required diameter of the column?

a$.450mm$

c$.475mm$

b$.500mm$

d$.425mm$

How many $20mm$ diameter bars are

required?

a$.14$

c$.16$

b $15$

d $17$