Reinforced concrete foundations, or also known as footings, transmit loads from a structure to the supporting soil. Footings are designed based on the nature of the loading, the properties of the footing and the properties of the soil. Footing design usually consists the following steps:
1. Determine the requirements for the footing, including the loading and the nature of the supported structure.
2. Select options for the footing and determine the necessary soils parameters.
3. The geometry of the foundation is selected so that any minimum requirements based on soils parameters are met. Following are typical requirements:
? The calculated bearing pressures need to be less than the allowable bearing pressures. Bearing pressures are the pressures that the footing exerts on the supporting soil. Bearing pressures are measured in units of force per unit area, such as pounds per square foot.
? The calculated settlement of the footing, due to applied loads, needs to be less than the allowable settlement.
? The footing needs to have sufficient capacity to resist sliding caused by any horizontal loads.
? The footing needs to be sufficiently stable to resist overturning loads. Overturning loads are commonly caused by horizontal loads applied above the base of the footing.
? Local conditions.
? Building code requirements.
4. Structural design of the footing is completed, including selection and spacing of reinforcing steel in accordance with ACI 318 and any applicable building code. During this step, the previously selected geometry may need to be revised to accommodate the strength requirements of the reinforced concrete sections.