Pad foundations are used to support individual or multiple columns, spreading the load to the ground below. They are generally square or rectangular in plan, with the plan area being determined by the permissible bearing pressure of the soil. The shape in plan will be dictated by the arrangement of the columns and the load to be transferred into the soil.
The thickness of the slab must be sufficient to ensure distribution of the load. The top of the pad may be sloping (i.e. the pad is thicker in the centre than it is at the edge). This is an economic solution, although there may be construction problems involved with casting the slope.
In simple cases the pad may be constructed from mass concrete. In general, some reinforcement (either welded steel fabric or reinforcing bars, depending on the loads involved) will be required in both directions. For design purposes, the pad is treated as if it were an inverted cantilever carrying the soil pressure and supported by the column.
Strip foundations are used to support walls or closely spaced rows of columns.
BRE Good Building Guide 39 Part 2 Simple foundations for low-rise housing: `rule of thumb` design. See BRE Bookshop
Good Concrete Guide 9 Designed and detailed (Eurocode 2) shows how to apply the principles of limit state design by means of simple worked examples.