A plain concrete footing made of M20 concrete is subjected to uniform ...
fck = 20 MPa
D = 700 mm
q
o = 7 Mpa
∴ tan α = 700/L ⇒ L = 129.6 ≃ 130mm
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A plain concrete footing made of M20 concrete is subjected to uniform ...
To determine the permissible maximum projection beyond the face of the column for a plain concrete footing, we need to consider the given parameters and apply the appropriate design criteria.
Given:
- Concrete grade: M20
- Uniform pressure: 7 MPa
- Total depth of footing: 700 mm
The permissible maximum projection beyond the face of the column can be determined by considering the depth of the footing and the strength of the concrete.
1. Determining the Permissible Stress of Concrete:
The permissible stress of concrete for M20 grade can be determined using the formula:
Permissible stress = 0.67 * characteristic strength of concrete
For M20 grade concrete, the characteristic strength is 20 MPa.
Permissible stress = 0.67 * 20 MPa = 13.4 MPa.
2. Determining the Maximum Pressure on the Footing:
The maximum pressure on the footing can be calculated using the formula:
Maximum pressure = Uniform pressure * Depth of footing
Maximum pressure = 7 MPa * 700 mm = 4900 kN/m2 = 4.9 MPa
3. Comparing the Maximum Pressure with Permissible Stress:
Now, we compare the maximum pressure on the footing with the permissible stress of the concrete.
If the maximum pressure is less than or equal to the permissible stress, the footing is safe. However, if the maximum pressure exceeds the permissible stress, the footing is not safe.
In this case, the maximum pressure on the footing is 4.9 MPa, which is less than the permissible stress of 13.4 MPa. Therefore, the footing is safe.
4. Determining the Permissible Maximum Projection:
The permissible maximum projection beyond the face of the column is determined as a fraction of the total depth of the footing.
For M20 grade concrete, the permissible maximum projection is given by the formula:
Permissible maximum projection = (Permissible stress / Maximum pressure) * Total depth of footing
Permissible maximum projection = (13.4 MPa / 4.9 MPa) * 700 mm
Permissible maximum projection = 2.7347 * 700 mm = 1914.29 mm ≈ 1914 mm
Therefore, the permissible maximum projection beyond the face of the column is approximately 1914 mm.
Hence, none of the given options (a, b, d) are correct. The correct answer is option 'C' (130 mm).