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
1) Shallow Foundation System – these types of
foundations are used where the soil bearing
capacity is high ,
Combined and isolated footing
2) Deep Foundation System
ii) Diaphragham wall
iii) Pile walls
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
broad area under the building
It Most common type of foundation used due to their low cost & ease of
Spread footings may be built in different shapes & sizes to accommodate
individual needs such as the following:
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
CONTINUOUS SPREAD FOOTINGS / STRIP FOUNDATION
Used to support bearing walls
support more than one column
useful when columns are located too close
together for each to have its own footing
RING SPREAD FOOTINGS
continuous footings that have been wrapped into a circle
commonly used to support the walls above-ground circular storage
The contents of these tanks are spread evenly across the total base
area and this weight is probably greater that the tank itself
Therefore the geotechnical analyses of tanks usually treat them as
circular foundations with diameters equal to the diameter of the tank
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.
During construction pumping is necessary – adds to the cost of construction.
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 loaded
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.