Determine the positive design moment capacity $(\backslash$Phi Mn$)$ for the continuous T$-$beam shown below. Assume the clear span of the beam $($ln$)$ is $23$ and the clear spacing between adjacent T$-$beam webs $($sw$)$ is $9$ when determining bf$.$ The concrete compressive strength is $4,000$ psi and the steel rebar is Gr$.60.$