A concrete beam prestressed with a parabolic tendon is shown in the sketch. The eccentricity of the tendon is measured from the centroid of the cross section. The applied prestressing force at service is 1620 KN. The uniformly distributed load of $$\frac{45KN}{m}$$ includes self weight.
The stress (in $$\frac{N}{mm^{2}}$$) in the bottom fibre at Mid Span is
