A singly-reinforced rectangular concrete beam of width 300 mm and effe...
B = 300 mm
d = 400 mm (effective depth)
M25 and Fe500
= 1142.64 mm
2Number of 16 mm
For
maximum number of bars to be provided is 5.
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A singly-reinforced rectangular concrete beam of width 300 mm and effe...
To determine the maximum number of reinforcing bars that can be provided in a singly-reinforced rectangular concrete beam, we need to consider the code provisions and design parameters. Let's go through the steps involved in the design process:
1. Given data:
- Width of the beam (b) = 300 mm
- Effective depth of the beam (d) = 400 mm
- Grade of concrete (M25)
- Grade of reinforcing steel (Fe500)
- Diameter of reinforcing bars (ϕ) = 16 mm
2. Limiting values:
- The limiting strain in concrete (ε_cu) is taken as 0.0035.
- The maximum allowable stress in steel (σ_st) is taken as 0.87 times the yield stress (σ_y) of the steel.
3. Calculation of modular ratio (m):
- The modular ratio (m) is given by the formula: m = 280/3√f_ck
- Here, f_ck is the characteristic compressive strength of concrete at 28 days.
- For M25 grade concrete, f_ck is 25 N/mm².
- Substituting the value, we get m = 280/3√25 = 9.14 (approx.)
4. Calculation of moment of resistance (M_u):
- The moment of resistance (M_u) is given by the formula: M_u = σ_st * A_st * (d - (σ_st * A_st) / (m * b))
- Here, A_st is the area of steel reinforcement.
- The area of one 16 mm diameter reinforcement bar can be calculated as A_st = (π * ϕ²) / 4.
- Substituting the values, we get A_st = (π * 16²) / 4 = 201.06 mm².
- Substituting the values in the moment of resistance formula, we get M_u = 0.87 * 250 * 201.06 * (400 - (0.87 * 250 * 201.06) / (9.14 * 300))
- Calculating this value, we get M_u = 1,440,000 Nmm.
5. Calculation of bending moment (M):
- The bending moment (M) is given by the formula: M = (w * l²) / 8.
- Here, w is the uniformly distributed load and l is the span of the beam.
- As the load and span are not provided in the given data, we cannot calculate the exact bending moment.
6. Calculation of the maximum number of reinforcing bars:
- The maximum number of reinforcing bars (n) can be calculated as n = M / M_u.
- Since we do not have the value of M, we cannot calculate the exact number of reinforcing bars. However, we can determine the range of n.
- From experience, it is known that for under-reinforced beams, the value of n is usually between 0.8 and 0.9.
- Substituting these values, we get 0.8 ≤ n ≤ 0.9.
7. Determination of the maximum number of reinforcing bars:
- Considering the range of n, the maximum number of reinforcing bars that can be provided is usually