# ASDIP Foundation – Spread Footings Design

##### About ASDIP Foundation:Overview | Benefits | Features | DocumentationModules:Spread Footings Design | Strap Footings Design | Combined Footings Design

The foundation is that part of the structure, which is usually placed below the ground surface and transmits the load to the underlying soil. If satisfactory soil directly underlies the structure, it is merely necessary to spread the load, by footings or other means, in order to reduce the bearing pressure and therefore prevent excessive settlement or rotation.

This module computes the soil bearing pressures induced by a square or rectangular spread concrete footing subject to vertical load and biaxial moment, and analyzes the stability of the structure in overturning, sliding and uplift. In addition, it performs the concrete design based on the Ultimate Strength Design Method of the ACI 318. Load combinations per the ASCE 7. The column may be eccentric in two directions.

The footing is assumed to be perfectly rigid with constant thickness, and rotates about its mass center to maintain the equilibrium of forces. A remarkable feature of the program is its ability to determine the soil pressures under the footing with any service load combination, including uplift loading. The pressures may also be calculated when only a part of the footing is in contact with soil (partial bearing). This is especially useful when a footing with small vertical load and big moments is designed, such as a footing at the corner of a building under lateral loads.

### Input Data

The required input data includes the footing and column dimensions, the materials’ properties, the allowable soil bearing pressure, and the acting service and factored loads. In addition, the program accepts a number of load cases, such as dead, live, snow, wind and seismic to be combined internally. Alternatively, you can model a single set of pre-combined loads.

### Example

Consider a 12′ x 8′ x 16″ spread concrete footing with a soil cover of 1′-0″. subjected to the following loads applied at the top of the footing: P=100 k, Mx=50 k-ft, Mz=60 k-ft, Pu=140 k, Mux=100 k-ft, Muz=100 k-ft. Per the soils report, the gross allowable soil bearing pressure is 3.0 ksf.

Verify the stability, find out the adequacy of the footing dimensions and design the steel reinforcement. The 16″ x 16″ concrete column is eccentric 6″ in both directions.

### Output

The program checks the footing stability in overturning, sliding and uplift for the service combined loads, and performs the concrete design, which includes the one-way shear, punching shear and bending for the factored combined loads. In each case the controlling load combination is identified and reported.

In case of partial bearing, the software accurately calculates the bearing pressure distribution on the base of the footing. The one-way shear, the punching shear, and the bending moments are calculated based on the bearing pressures under the factored loads. The program uses a sophisticated algorithm based on integrals to find the areas, volumes, and centroids of these irregular resulting geometric shapes.

A detailed step-by-step report is available to the touch of a tab, which is updated with every new change. In addition, ASDIP Foundation uses a pre-formated colorful text-with-values output for easier identification of the problem areas.

ASDIP Foundation generates a graphical view of the designed footing and the resulting pressures and forces, as shown. The program also generates the moment and the shear plan views for the controlling combination, as well as a view of the construction section and elevation with the reinforcement information.

For a more detailed information on spread footings subjected to biaxial bending please refer to our blog post.