building construction

2. Introduction
Foundations ( sub structure) is the lower
portion the building , usually located below
ground
level, which transmits the load of the super
structure to the sub soil a foundation is
therefore
that part of the structure which is in direct
contact with the ground to which the loads
aretransmitted.
The soil which is located immediately
below the base of the foundation is called
the sub-soil
or foundation soil, while the lowermost
portions of the foundation which is in direct
contact
with the sub soil is called the footing.

3. Functions of foundations
The basic function of a foundation is to transmit
the dead loads, super – imposed loads (or live
loads) and wind loads from a building to the soil
on which the building rests.
Foundation serves the following purposes:
1. Reduction of load intensity
Foundations distribute the loads of the super
structure, to a larger area so that the intensity of
the
load at its base does not exceed the safe bearing
capacity of the soil.
2. Even distribution of load
Foundations distribute the non – uniform loads
of the super structure evenly to the sub-soil
3. Provision of level surface
Foundation provide leveled and hard surface
over which the super-structure can be built.

4. 4. Lateral stability
It anchors the super structure to the ground, thus imparting lateral stability to
the superstructure.
5. Safety against under mining
It provides the structural safety against undermining due to burrowing animals
and flood water.
6. Protection against soil movements
Special foundations measures prevents or minimizes the distress (or cracks) in
the superstructure,
due to expansion of the sub soil because of moisture movement in same
problematic
soils.
Functions of foundations

5. Foundation loads
Dead Load
this is the load of the material used for the various components of a building
such as
walls, floors, roofs, etc. all permanent loads are thus included in dead load.
Live Load
this is the movable load on the floor and hence its variable. Its also sometimes
known as
the super imposed load. It includes the load of persons standing on a floor,
weight of the
material stored on a floor, weight f snow on a roof, etc.
Wind Load
In case of tall buildings, the effect due to wind should be considered.
Structural Member Forces
Uplift
Earthquake
Horizontal and vertical forces caused by the motion of the ground relative to the
building.

6. Types of foundations

7. Definition –
Footings are structural members used to support columns
and walls and to transmit and distribute their loads to the
soil in such a way that the load
bearing capacity of the soil is not exceeded, excessive
settlement, differential settlement,or rotation are prevented
and adequate safety against overturning or sliding is
maintained.
Footing

8. Wall footings are used to
support structural walls that
carry loads for other floors
or to support nonstructural
walls.
Wall footings

9. Isolated or single footings
are used to support single
columns. This is one of the
most economical types of
footings and is used when
columns are spaced at
relatively long distances.
Isolated or single footings

10. Combined footings usually
support two columns, or
three columns not in a row.
Combined footings are used
when tow columns are so
close that single footings
cannot be used or when one
column is located at or near
a property line.
Combined footings

11. Cantilever or strap footings
consist of two single
footings connected with a
beam or a strap and support
two single columns. This
type replaces a combined
footing and is more
economical.
Cantilever or strap footings

12. Continuous footings
support a row of three or
more columns. They have
limited width and continue
under all columns.
Continuous footings

13. Rafted or mat foundation
consists of one footing
usually placed under the
entire building area.
They
are used, when soil bearing
capacity is low, column
loads are heavy single
footings cannot be used,
piles are not used and
differential settlement must
be reduced.
Rafted or mat foundation