Design of Combined Footing

Combined footing is a type of foundation that is used when two or more columns are supported by a single footing. It is designed to distribute the load from the columns evenly to the underlying soil. In the design of combined footing, it is important to consider the distribution of soil pressure to ensure the stability and safety of the structure.

Resultant of Column Loads

The resultant of the column loads refers to the combined effect of all the loads acting on the columns. It represents the total vertical force that needs to be supported by the footing. The position of the resultant is an important factor in the design of the footing.

Centre of Gravity of the Footing Slab

The centre of gravity of the footing slab is the point at which the entire weight of the footing can be assumed to act. It is the point through which the resultant of the column loads should pass to ensure an even distribution of soil pressure.

Net Soil Pressure

The net soil pressure is the pressure exerted by the footing on the underlying soil. It is calculated by dividing the total load supported by the footing by the area of the footing. The distribution of soil pressure affects the stability and settlement of the foundation.

Uniform Soil Pressure

In the case of a combined footing, the ideal scenario is to have a uniform soil pressure. This means that the net soil pressure is constant throughout the footing area. Uniform soil pressure ensures equal settlement of the footing and prevents excessive stress concentration in certain areas.

Explanation of the Correct Answer

The correct answer for this question is option 'C' - Uniform. The net soil pressure obtained in the design of a combined footing is typically uniform. This is because the resultant of the column loads is designed to pass through the centre of gravity of the footing slab. When the resultant passes through the centre of gravity, it ensures an even distribution of soil pressure over the entire footing area.

Uniform soil pressure is desirable in the design of combined footings as it helps to minimize differential settlement and prevents the formation of weak zones in the soil. It provides a stable foundation for the columns and ensures the structural integrity of the building.

In conclusion, the correct answer for this question is option 'C' - Uniform. The net soil pressure obtained in the design of combined footing is uniform due to the positioning of the resultant of the column loads at the centre of gravity of the footing slab. This ensures an even distribution of soil pressure and helps to maintain the stability and safety of the structure.