In a pre-stressed concrete beam section shown in the figure,

In a pre-stressed concrete beam section shown in the figure, the net loss is 10% and the final pre-stressing force applied at X is 750 kN. The initial fiber stresses (in N/mm² ) at the top and bottom of the beam were:

1. 4.166 and 20.833
2. – 4.166 and – 20.833
3. 4.166 and –20.833
4. – 4.166 and 20.833

Final force = 750 kN
Loss = 10%
∴ Initial force

Top and bottom stress

=	P	±	m
	A		Z

=	833.33	× 10^-3 ±	833.33 × 10³ × 100 × 6
	250 × 400		250 × 400²

= 8.33 ± 12.5
∴ Top stress = 8.33 – 12.5 = –4.17 (tension)
Bottom stress = 8.33 + 12.5 = 20.83 (compression)