$4-7$ Compute the negative$-$moment capacity, $M_n,$ and check $A_{s,\text{m}\text{i}\text{n}}$ for the beam

shown in Fig. P$4-7.$ Use $f_c^{\text{'}}=4500$ psi and $f_y=60,000.$

Compute the nominal moment capacity of the beam, $M_n,$ and the strength reduction

factor, $.$ This section is subjected to negative bending, so tension will develop in the top

flange and the compression zone is at the bottom of the section. ACI Code requires that a

portion of the tension reinforcement be distributed in the flange, so assuming that the No$.$

$7$ bars in the flange are part of the tension reinforcement: six No$.7$ bars