The cross-section at mid-span of a beam at the edge of a slab is shown in the sketch. $$A$$ portion of the slab is considered as the effective flange width for the beam. The grades of concrete and reinforcing steel are $$M25$$ and $$Fe415,$$ respectively. The total area of reinforcing bars $$\left( {{A_{st}}} \right),$$ is $$\,4000\,\,m{m^2}.$$ At the ultimate limit state, $${x_u}$$ denotes the depth of the neutral axis from the top fibre. Treat the section as under-reinforced and flanged $$\left( {{x_u} > 100\,\,mm} \right).$$

The value of $${{x_u}}$$ (in $$mm$$) computed per the Limit State Method of $$IS$$ $$456:2000$$ is

An isolated $$T$$ beam is used as a walkway. The beam is simply supported with an effective span of $$6$$ $$m.$$ The effective width of flange, for the cross-section shown in figure, is