The resultant compression forces in concrete and compression steel respectively for a doubly reinforced rectangular beam is (width of the beam = b', depth of neutral axis = xu, Area of compression steel = ASC', Stress in compression steel = fsc)
1
0.447 fckbxu, Asc (fsc - 0.447 fck)
2
0.362 fckbxu, Asc (fsc - 0.447 fck)
3
0.447 fckbxu , Asc (fsc - 0.362fck)
4
0.362 fckbxu, Asc (fsc - 0.362 fck)