ANS:B -

To determine the overall depth of a combined footing under a column based on punching shear consideration, we need to consider the punching shear resistance provided by the footing and ensure it is adequate to resist the applied load from the column. Let's denote the following variables:

• q = punching shear resistance per unit area of the footing.
• Ac​ = critical section area of the footing.
• W = applied load from the column.
• D = overall depth of the combined footing.

The punching shear resistance (V) of the combined footing is given by: V=q×Ac​ To ensure that the combined footing is adequate to resist punching shear, the punching shear resistance (V) should be greater than or equal to the applied load (W) from the column. Therefore, we have: q×Ac​≥W We can express the critical section area Ac​ of the combined footing in terms of its overall depth D. Assuming a rectangular footing, the critical section area can be expressed as the product of the width (b) and the overall depth (D). Ac​=b×D Substituting this expression into the inequality above, we get: q×(b×D)≥W Now, we can solve for the overall depth D: D≥q×bW​ Therefore, the overall depth D of the combined footing under column A, based on punching shear consideration, should be greater than or equal to the ratio of the applied load (W) from the column to the punching shear resistance per unit area (q) of the footing multiplied by the width (b) of the footing. Please note that the actual design of the combined footing may involve additional considerations, such as bearing capacity, settlement, and structural stability, which should also be taken into account during the design process.