Concept:
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Loss of prestress in any wire = m fcs where m is modular ratio & fcs is stress in concrete at the level of steel/wire.
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The three wires are tensioned one-by-one. so, when wire 2 is tensioned mere is a loss of stress in wire (1) & also when wire (3) is tensioned, there is a loss of stress in wires (1) & (5). There is no loss of stress in the wire(3).

P1, P2, P3 are forces in wires 1,2,3 respectively.
Loss in wire (1) due to P2 and P3 or (P2+P3)
Loss in wire (2) is due to P3 only.
Loss in wire (3) is zero.
3) P1=P2=P3=P=(1000200×1500)kN=300,kN (given)
- (P = Area of pre-stress × pre-stress)
Calculation

Total stress, fcs=AP+IPe2
- Loss in wire (1) is due to P2+P3 = 2P; substitute 'P' in above with 'gp'
fcs1=A2P+I2Pe2
=(450×4502×300×100;);+12450×(450)32×300×(100)2−3.96+1.76
= 4.72 N/mm2
Loss L1=mfcs1=6×4.72=28.32,N/mm2
L2=mfcs2=6×2.36=14.16,N/mm2
L3=mfcs3=6×0=0
Ag Loss = =328.32+14.16+0=14.16,N/mm2
Loss in wire (2) is due to P3=P=300,kN.
fcs2,=,450×450300×1000,+,12450×(450)3300×1000×(100)2