Question

A concrete column carries an axial load of 450 kN and a bending moment of 60 kNm at its base. An isolated footing of size $2m\times 3m$ with the 3 m side along the plane of the bending moment is provided under the column. Centres of gravity of the column and footing coincide. The net maximum and minimum pressures, in kPa, on the soil under the footing are, respectively.

• A. 95 and 75
• B. 75 and 55
• C. 95 and 55
• D. 75 and 75

Answer 1

The correct option is C 95 and 55


$\begin{array}{cc}\text{Extreme stress}& =(\frac{P}{A}\pm \frac{My}{I})\\ & =\frac{450}{3\times 2}\pm \frac{60\times 1.5\times 12}{2\times 3^3}\\ & =(75\pm 20)kPa\\ \therefore \text{Maximum stress}& =75+20=95kPa\\ \text{Minimum stress}& =75-20=55kPa\end{array}$