$(1)$

$f_c^{\text{'}}=4000$

Grade $60$ steel

NWC

$M_n=?$

$(2)$

$f_c^{\text{'}}=4000$ psi

Grade $60$ steel

NWC

$M_n=$

spiral stirrups.

$(3)$

$f_c^{\text{'}}=3000.$

Grade $60$ steel

NWC

$M_n=?$

$(4)$ Why does the ACI code specify that a certain mininum percontage of Reinforcing be useld in beams?