Minimum Clear Cover for Main Steel Bars

In reinforced concrete structures, clear cover refers to the distance between the outer surface of the concrete and the main steel bars or reinforcement. This clear cover is essential to protect the steel bars from corrosion, fire, and other environmental factors. Different elements of a structure, such as slabs, beams, columns, and footings, require different minimum clear covers to ensure the durability and safety of the structure.

Below is the correct answer for the minimum clear cover (in mm) to the main steel bars in slab, beam, column, and footing respectively:

Option B: 15, 25, 40, 75

Now, let's understand the reasons behind these specific clear cover requirements for each structural element:

Slab:
- Slabs are the horizontal members that transfer load to the beams and columns.
- The minimum clear cover for the main steel bars in slabs is 15 mm.
- This cover is sufficient to protect the steel bars from moisture, temperature variations, and minor mechanical damage.
- However, in areas with higher exposure to corrosive agents or aggressive environmental conditions, a greater clear cover may be required.

Beam:
- Beams are the horizontal or inclined members that support the load from the slabs and transfer it to the columns.
- The minimum clear cover for the main steel bars in beams is 25 mm.
- Beams are subjected to higher loads and bending moments compared to slabs.
- A greater clear cover helps in providing better fire resistance and protection against corrosion.

Column:
- Columns are the vertical members that provide support to the entire structure.
- The minimum clear cover for the main steel bars in columns is 40 mm.
- Columns experience higher compressive forces and are critical for the stability of the structure.
- A larger clear cover ensures better fire resistance, protection against corrosion, and enhances the durability of the structure.

Footing:
- Footings are the structural elements that transfer the load from the columns to the soil.
- The minimum clear cover for the main steel bars in footings is 75 mm.
- Footings are in direct contact with the soil and are exposed to moisture and other environmental factors.
- A greater clear cover is required to protect the steel bars from corrosion and provide longer durability.

It is important to note that these minimum clear covers are specified in the design codes and can vary based on the specific design requirements, environmental conditions, and exposure to corrosive agents. Therefore, it is crucial to consult the relevant design standards and guidelines to ensure the appropriate clear cover is provided for the main steel bars in each structural element.