$4-8.$ For the beam shown in Fig. P$4-8,f_{c^{\text{'}}}=4000$ psi and $f_y=60,000$psi.

$($a$)$ Compute the effective flange width at midspan.

$($b$)$ Analyze the beam for both positive$-$ and negative$-$moment regions. At the supports, the bottom bars are in one layer; at midspan, the No$.8$ bars are in the bottom, the No$.7$ bars in a

$($b$)$ Beam span supported by $18-$in$.$ wide columns