Chapter 7, Problem 7.16QPP

A building column carries a factored ultimate vertical downward load of 320 k. It is to be supported on a 3 ft deep, square footing. The soil beneath this footing has the following properties: $\gamma =20.5{\text{kN/m}}^{\text{3}},c\text{'}=5\text{kPa,}$ and $\varphi \text{'}=36°.$ The groundwater table is at a depth of 5 ft below the ground surface. Using LRFD, with a resistance factor of 0.5, compute the required footing width.