Chapter 7, Problem 7.24QPP

Two columns, A and B, are to be built 6 ft 0 in apart (measured from their centerlines). Column A has a vertical downward dead load and live loads of 90 k and 80 k, respectively. Column B has corresponding loads of 250 k and 175 k. The dead loads are always present, but the live loads may or may not be present at various times during the life of the structure. It is also possible that the live load would be present on one column, but not the other. These two columns are to be supported on a 4 ft 0 in deep rectangular spread footing founded on a soil with the following parameters: $\gamma =122{\text{lb/ft}}^{\text{3}},\varphi \text{'}=37°,$ and $c\text{'}=100{\text{lb/ft}}^{\text{2}}.$ The groundwater table is at a very great depth. Use ASD in this problem.

1. The location of the resultant of the loads from columns A and B depends on the amount of live load acting on each at any particular time. Considering all of the possible loading conditions, how close could it be to column A? To column B?
2. Using the results of part (a), determine the minimum footing length, L, and the location of the columns on the footing necessary to keep the resultant force within the middle third of the footing under all possible loading conditions. The footing does not need to be symmetrical. The footing must extend at least 24 in beyond the centerline of each column.
3. Determine the minimum required footing width, B, to maintain a factor of safety of at least 2.5 against a bearing capacity failure under all possible loading conditions.
4. If the B computed in part c is less than the L computed in part (b), then use a rectangular footing with dimensions $B\times L.$ If not, then redesign using a square footing. Show your final design in a sketch.