Design of Isolated Footing with Vertical Load Only – According to ACI 318M-99

Designing an isolated footing with vertical load only, according to ACI 318M-99 (American Concrete Institute Building Code Requirements for Structural Concrete), involves the following steps:

Determine the Design Load:

Identify the applied vertical load from the superstructure or column that the isolated footing will support.
Consider any additional loads, such as self-weight of the footing and superimposed dead loads.
Determine Footing Dimensions:

Determine the required footing dimensions based on the applied load and allowable bearing pressure of the soil.
Consider the soil properties, including bearing capacity and settlement criteria.
ACI 318M-99 provides guidance on determining minimum footing dimensions based on the applied loads and soil conditions.
Check Footing Stability:

Verify the stability of the footing against overturning, sliding, and bearing capacity failure.
Calculate the overturning moment caused by the applied load and check it against the resisting moment provided by the soil pressure distribution and footing dimensions.
Calculate the sliding force and compare it to the friction or resistance provided by the soil.
Determine Allowable Bearing Pressure:

Determine the allowable bearing pressure of the soil based on soil investigations and geotechnical analysis.
Ensure that the applied load does not exceed the allowable bearing pressure to avoid excessive settlement or failure.
Design Reinforcement:

Determine the required reinforcement for the footing based on the applied load, allowable bearing pressure, and footing dimensions.
Calculate the bending moment and shear forces in the footing.
Design the reinforcement to resist these forces, considering the concrete cover requirements and reinforcement detailing per ACI 318M-99.
Verify Footing Strength and Serviceability:

Check the footing strength by comparing the design ultimate moment and shear forces to the capacity of the reinforcement.
Ensure that the footing satisfies the deflection and crack width requirements for serviceability.
Provide Construction Details:

Prepare construction details for the footing, including reinforcing bar sizes, spacing, and concrete cover.
Consider construction joints, formwork requirements, and any specific construction considerations specified in ACI 318M-99.