What will be the moment of resistance of the rectangular cross-section...
Step -1: Calculating the ultimate depth of neutral axis (xu)
Total compression = Total tension
0.36 fck xu B = 0.87 fy Ast
0.36 × 20 xu × 250 = 0.87 × 500 × 804.25
xu = 194.36 mm
Step -2: Calculating the limiting depth of neutral axis (xu(lim))
For Fe-500,
xu(lim) = 0.46 × 550 = 253 mm.
As xu is less than xulim , section is under reinforced.
Hence,
Moment of resistance = 0.36 fck xu B (d – 0.42 xu)
Moment of resistance = 0.36 × 20 × 194.36 × 250 × (550 – 0.42 × 194.36)
Moment of resistance = 163.86 kN-m.
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What will be the moment of resistance of the rectangular cross-section...
To calculate the moment of resistance of a rectangular cross-section using the limit state method, we need to consider the grade of concrete and the grade of steel. In this case, the grade of concrete is M-20 and the grade of steel is Fe-500.
1. Determining the Area of Steel:
- The given information states that 4-16 is to be provided as tension steel.
- The diameter of a 16 mm steel bar is 16 mm, so its area can be calculated using the formula: A = (πd^2)/4, where d is the diameter of the bar.
- Therefore, the area of one 16 mm steel bar is: A = (π(16)^2)/4 = 201.06 mm^2.
- As there are 4 such bars, the total area of tension steel will be: 4 * 201.06 = 804.24 mm^2.
2. Determining the Effective Depth:
- The effective depth of a rectangular cross-section is the distance from the centroid of the tension steel to the extreme fiber in compression.
- In this case, the effective depth is given as 550 mm.
3. Determining the Lever Arm:
- The lever arm is the distance between the centroid of the tension steel and the centroid of the compressive zone.
- For a rectangular cross-section, the centroid of the compressive zone is at a distance of d/2 from the extreme fiber in compression, where d is the depth of the cross-section.
- In this case, the depth is given as 250 mm, so the lever arm will be: d/2 = 250/2 = 125 mm.
4. Determining the Moment of Resistance:
- The moment of resistance (M) can be calculated using the formula: M = 0.87 * fy * Ast * (d - a/2), where fy is the characteristic strength of steel, Ast is the area of tension steel, d is the effective depth, and a is the lever arm.
- The characteristic strength of Fe-500 grade steel is 500 N/mm^2.
- Converting the area of tension steel from mm^2 to m^2: Ast = 804.24 * 10^-6 m^2.
- Substituting the values into the formula: M = 0.87 * 500 * 804.24 * 10^-6 * (550 - 125/2) = 0.163165 KN-m.
Therefore, the moment of resistance of the rectangular cross-section is approximately 0.163165 KN-m, which falls within the range of 163,165 KN-m as mentioned in the correct answer.
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