Direction: Assume straight line instead of parabola for stress-strain curve of concrete as follows and partial factor for safety as 1.0.
A rectangular under-reinforced concrete section of 300 mm width and 500 mm effective depth is reinforced with 3 bars of grade Fe G15, wach of 16 mm diameter. Concrete mix is M20.
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The depth of neutral axis from the compression fibre is
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- 76 mm
- 81 mm
- 87 mm
- 100 mm
Correct Option: A
Tension force = compression force
0.87 fy Ast = 0.67 fck (b.x2) + (1/2)0.67 fck(bx1)
| = | ||||
| y | 0.0020 |
| ∴ x1 = | xu x2 = | xu | ||
| 7 | 7 |
| 0.87 × 415 × 3 × | × 162 | 4 |
= 0.67 × 20 × 300 × (3/7) xu + (1/2) × 0.67 × 20 × 300 × (4/7) xu
∴ xu = 76 mm
