Please use this material factor :

Concrete C25 fck = 25 MPa, ?mc= 1,5

fcd =fck/?mc=25/1,5= 16,66

Stell S420 fyk = 420 MPa, ?mc= 1,15

fyd =fyd/?mc=420/1,15= 365,2

k1 = 0,85 ? 0,006(fck ? 25), since fck = 25 ? 25, than the k1 =0,85Es = 2 ? 105 MPa, ?sy =fyd/Es=365,2 / 2?10^5= 0,001825

For the beam section given: Concrete is C30 and longitudinal reinforcement is S420 steel and total tension steel area As =3500 mm and compressive steel area is As'= 400 mm. Using TS500 material factors, find moment capacity of the section. The compression steel location d'= 120 mm. If compression steel does not yield, solve using trial-error approacch for compression zone "c". Concrete C30 Steel S420 bw= 400 mm As' As O Q d =800 mm