Structure foundation

                                                     FOUNDATION

 STRUCTURE  FOUNDATION

A foundation is a lower portion of building structure that transfers its gravity loads to the earth. Foundations are generally broken into two categories :  shallow foundation and deep foundations… When the concrete dries, the steel acts like the bones in our body to tie the foundation together.

TYPES OF FOUNDATION AND THEIR USES

Following are different types of foundation used in construction:

Ø  SHALLOW FOUNDATON

·         Individual footing or isolated footing.

·         Combined footing.

·         Strip foundation.

·         Raft or mat foundation.

Ø   DEEP FOUNDATION

·         Pile foundation.

·         Drilled Shafts or caissons.

TYPES OF SHALLOW FOUNDATIONS

1. INDIVIDUAL FOOTING OR ISOLATED FOOTING:-

Individual footing or an isolated footing is the most common types of foundation used for building construction. This foundation is constructed for single column and also called as pad foundation.

The shape of individual footing is square or rectangle and is used when loads from structure is carried by the columns. Size is calculated based on the load on the column and safe bearing capacity of soil.

Rectangular isolated footing is selected when the foundation experiences moments due to eccentricity of loads or due to horizontal forces .

For example:- consider a column with vertical load of 200kN and safe bearing capacity of 100KN/M² then the area of the footing required will be 200/100 =2m². So for a square footing. Length and width of footing will be 1.414m x 1.414.

2. COMBINED FOOTING:-

Combined footing is constructed when two or more columns are closed enough and their isolated footings overlap each other. It is a combination of isolated footing, but their structural design differs.

The shape of this footing is rectangle and is used when loads from structure is carried by the columns.

3. SPREAD FOOTING OR STRIPS FOOTINGS AND WALL FOOTINGS:-

Spread footings are those whose base is more wider than a typical load bearing wall foundations. The wider base of this footing type spread the weight from the building structure over more area and provides better stability.

Spread footings and wall footings are used for individual columns, wall and bridges piers where the bearing soil layer is within 3m (10feet) from the ground surface. Soil bearing capacity must be sufficient to support the weight of the structure.

These should not be used on soils where there is any possibility of ground flow of water above bearing layer of soil which may result in scour or riquefaction.

4. RAFT AND MAT FOUNDATION:-

Raft or mat foundation are the types of foundation which are spread across the entire area of the building to support heavy structure loads from columns and walls.

The used of mat foundation is for columns and walls foundations where the loads from structure on columns and walls are very high. This is used to prevent differential. Settlement of individual footing, thus designed as a single mat (or combined footing) of all the loads bearing elements of the structure.

TYPES OF DEEP FOUNDATION

1. PILE FOUNDATION:-

Pile foundation is a type of deep foundation which is used to transfer heavy loads form the structure to hard rock strata much deep below the ground level.

Pile foundations are used to transfer heavy loads of structures through columns to hard soil strata which is much below  ground level where shallow foundation such as spread footings and mat footings cannot be used. This is also used to prevent uplift of structure due to lateral loads such as earthquake and wind forces.

2. DRILLED SOFTS OR CAISSON FOUNDATION:-

Drilled shafts, also called as caissons, is a types of deep foundation and has action similar to pile foundation discussed above, but are high capacity cast-in-situ foundations, it resists loads from structure through shaft resistance,