The four$-$span slab shown supports a live load of $3k\frac{N}{m}2,$ plus floor finishes and ceiling load of $1k\frac{N}{M}2.$ Assume $1hr$ fire resistance and mild exposure. The Fcu$=30\frac{N}{m}m2$ and $Fy=500\frac{N}{m}m2,$ Fyv $=250\frac{N}{m}m2.$ Design a typical internal beam$($B$1).$

Note: The slab thickness $=175mm,$ columns are $300$ by $300$