B.ARCH 3RD YR
INTRODUCTION TO FOUNDATION
The lowest part of a structure is generally referred to as foundation.
FUNCTION OF FOUNDATION
To transfer load of the superstructure to the soil on which it is resting
A properly designed foundation is one that transfers the structural load
throughout the soil without overstressing of soil which can result in
either excessive settlement or shear failure,
both of which can damage the structure.
LOADS AND SETTLEMENT OF FOUNDATIONS
Types of loads on foundations
Dead, live, wind, inclined thrusts and uplift, water table and earthquake
Types of settlements
Uniform and differential - Differential settlement must be minimized,
depends on site soil conditions and distribution of loads on columns
supporting the building
TYPES OF FOUNDATION
Foundations are classified as
SHALLOW FOUNDATION AND
1. Shallow foundation- It has a smaller depth limited to the depth of the
footing. It spreads the load from superstructure on a larger area of soil.
They are classified as
a. Isolated footing
b. Combined footing
An isolated footing supports one
wall or one column .either flat
Or stepped which distribute the
Load of wall to the soil. An
Isolated footing supporting a
Single column is commonly
Used where the loads on column are
Small and columns are not closely
Spaced. They are of the following
Footing for column
Footing for wal
SQUARE SPREAD FOOTINGS / PAD FOUNDATION
support a single centrally located column
use concrete mix 1:2:4 and reinforcement
the reinforcement in both axes are to resist/carry tension loads.
RECTANGULAR SPREAD FOOTINGS
Useful when obstructions prevent construction of a square footing with
a sufficiently large base area and when large moment loads are present
CIRCULAR SPREAD FOOTINGS
are round in plan view
most frequently used as foundation for light standards, flagpoles and power
SPREAD FOOTING FOUNDATION
Also known as a footer or footing
It’s an enlargement at the bottom of a column/ bearing wall that
spreads the applied structural loads over a sufficiently large soil area.
Each column & each bearing wall has its own spread footing, so each
structure may include dozens of individual footings.
The spread foundation consists of
concrete slabs located under each
structural column and a continuous
slab under load-bearing walls.
For the spread foundation system
the structural load is literally
spread out over a
area under the building
It is most common type of
foundation used due to their low
cost & ease of construction.
Combined footing supports two or more columns.
Combined footing supporting two columns may be used for column on
When the bearing capacity of
the soil is low , then continuous
strip footings supporting more
than two columns in a row are
provided. Such strip footings
more than two columns in both
the directions are known as
A foundation system in which essentially the entire building is placed on a
large continuous footing.
It is a flat concrete slab, heavily reinforced with steel, which carries the
downward loads of the individual columns or walls.
Raft foundations are used to spread the load from a structure over a large
area, normally the entire area of the structure.
It is normally consists of a concrete slab which extends over the entire
It may be stiffened by ribs or beams incorporated into the foundation.
Raft foundations have the advantage of reducing differential settlements as
the concrete slab resists differential movements between loading positions.
They are often needed on soft or loose soils with low bearing capacity as
they can spread the loads over a larger area.
DEPTH AND LOCATION OF FOUNDATION
Depth and location of foundation depends on
Zone of significant volume changes in soil.
Adjacent structures and property lines.
Adjacent structures and property lines.
Structures may be damaged by the construction of new foundations, as a result
of vibrations, undermining by excavation or lowering of the water table. After
new foundations have been constructed, the (new) loads they place on the soil
may cause settlement of previously existing structures as a result of new stress
pattern in the surrounding soil.
In general, deeper the foundations and closer to the old structure, greater will
be the potential for damage to old structures.
Presence of water reduces soil bearing
capacity, larger footing size more cost.
necessary – adds to the cost of