Assume straight line instead of parabola for stress-strain curve of co...
Introduction:
To calculate the depth of the neutral axis of a rectangular under-reinforced concrete section, we need to consider the stress-strain curve of concrete, the partial factor of safety, and the dimensions and reinforcement details of the section.
Given:
- Width of the section (b): 300 mm
- Effective depth of the section (d): 500 mm
- Grade of reinforcement bars: Fe-415
- Diameter of reinforcement bars (D): 16 mm
- Concrete mix: M20
- Partial factor of safety: 1.0
Calculating the area of steel reinforcement:
The area of steel reinforcement can be calculated using the formula:
A_s = (π/4) * D^2 * n
where A_s is the area of steel reinforcement, D is the diameter of the reinforcement bars, and n is the number of reinforcement bars.
In this case, the area of steel reinforcement is:
A_s = (π/4) * (16 mm)^2 * 3 = 603.19 mm^2
Calculating the area of concrete:
The area of concrete can be calculated using the formula:
A_c = b * d - A_s
where A_c is the area of concrete, b is the width of the section, d is the effective depth of the section, and A_s is the area of steel reinforcement.
In this case, the area of concrete is:
A_c = (300 mm) * (500 mm) - 603.19 mm^2 = 149396.81 mm^2
Calculating the stress in concrete:
The stress in concrete can be calculated using the formula:
σ_c = f_c / γ_m
where σ_c is the stress in concrete, f_c is the characteristic compressive strength of concrete, and γ_m is the partial factor of safety.
In this case, the stress in concrete is:
σ_c = 16.7 MPa / 1.0 = 16.7 MPa
Calculating the strain in concrete:
Since we are assuming a straight line stress-strain curve for concrete, the strain can be calculated using the formula:
ε_c = σ_c / E_c
where ε_c is the strain in concrete and E_c is the modulus of elasticity of concrete.
The strain in concrete for a straight line curve can be calculated using the formula:
ε_c = (σ_c / f_cm) * (2 + 3 * (σ_c / f_cm)) / 2
In this case, the strain in concrete is:
ε_c = (16.7 MPa / 20 MPa) * (2 + 3 * (16.7 MPa / 20 MPa)) / 2 = 0.8385
Calculating the depth of the neutral axis:
The depth of the neutral axis can be calculated using the formula:
d_n = d * (1 - (ε_c / ε_cu))
where d_n is the depth of the neutral axis, d is the effective depth of the section, ε_c is the strain in concrete, and ε_cu is the ultimate compressive strain of concrete.
In this case, the ultimate compressive strain of concrete can be taken as 0.0035.
Calculating the depth of the neutral axis:
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