Design of Shallow Foundation (Isolated Footings)

PROCEDURE:

FOOTING:

          Footings and other foundation units transfer loads from the structure to the soil or rock supporting the structure. Because the soil is generally much weaker than the concrete columns and walls that must be supported, the contact area between the soil and the footing is much larger than that between the supported member and the footing.The more common types of footings are .Strip footings or wall footings display essentially one-dimensional action, cantilevering out on each side of thewall. Spread footings are pads that distribute the column load in two directions to an area ofsoil around the column. Sometimes spread footings have pedestals, are stepped, or are tapered to save materials. A pile cap transmits the column load to a series of piles, which, in turn, transmit the load to a strong soil layer at some depth below the surface. Combined footings transmit the loads from two or more columns to the soil. Such a footing is often used when one column is close to a property line. A mat or raft foundation transfers the loads from all the columns in a building to the underlying soil. Mat foundations are used when very weak soils are encountered. Caissons 2 to 5 ft in diameter are sometimes used instead of piles to transmit heavy column loads to deep foundation layers. Frequently, these are enlarged at the bottom (belled) to apply load to a larger area.
           The choice of foundation type is selected in consultation with the geotechnical engineer. Factors to be considered are the soil strength, the soil type, the variability of the soil type over the area and with increasing depth, and the susceptibility of the soil and the building to deflections. Strip, spread, and combined footings are considered in this chapter because these are the most basic and most common types.

DESIGN OF SQUARE FOOTING:

STEP-1:Size of the footing

STEP-2:Net upward pressure

STEP-3:Depth of the footing on the basic B.M.

STEP-4:Area of reinforcement

STEP-5:Check for one way shear

STEP-6:Check for two way shear

RESULT:

          Square footing has been designed successfully using given details