This document provides an overview of footings for reinforced concrete design. It discusses that footings transmit loads from columns, walls, or lateral loads to the soil. Footings must be designed to prevent excessive settlement or rotation and minimize differential settlement. There are different types of spread footings including wall footings, isolated column footings, combined footings, and mat or raft foundations. The document also covers load and bearing pressures, with equations to calculate the required footing size based on soil type and applied loads.

1. Reinforced Concrete Design-II
Lecture 07: Footings
Semester – Fall 2020
Dr.Tahir Mehmood
Reference
Design of Concrete Structures 14th Ed. by Nilson, Darwin and Dolan.

2. FOOTING

4.  Footing are structural elements that transmit to the soil
column loads, wall loads or lateral loads. If these loads are to
be properly transmitted, footing must be designed to prevent
excessive settlement or rotation and to minimize differential
settlement.
Introduction
 To limit settlement within tolerably small amount, it is
necessary.
i. To transmit the load of the structure to a soil stratum of
sufficient strength and
ii. To spread the load over a sufficiently large area of that
stratum to minimize bearing pressure.

5.  If satisfactory soil directly underlies the structure, it is merely
necessary to spread load by footings. Such substructure are
known as “spread foundation.”
Introduction
 If adequate soil is not found immediately below the
structure, if becomes necessary to use deep foundations such
as piles to transmit the load to deeper, firmer layers.

6. Type of Spread Footing
i. Wall Footing
 A wall footing is simply
a strip of reinforced or
plain concrete, wider than
the wall that distributes its
pressure.
ii. Isolated spread footing under
single column
 These may be usually square,
sometimes rectangular or occasionally
circular in plan.

7. Type of Spread Footing iii. Combined Footing
 Supporting two
or more column
loads. These may
be continuous
with a rectangular
or trapezoidal
plan or isolated
column footing
joined by a beam
which is referred
to as strap
footing.

8. iii. Mat or Raft Foundation
 Which is one large continuous footing supporting all
columns of the structure. This is used when the soil is poor.
Type of Spread Footing
Load, bearing Pressures & Footing Size
When the soil is
coarse grained
When the soil is
clayey or fine
grained
a
req
q
L
D
A

 3
5
.
2
q
q ult
a



9. Load, bearing Pressures & Footing Size
 D and L=loads (service) at the level of base of base of footing
 Eccentric load but e does not exceed the kern distance.
I
MC
A
P
q
min
max 

P
M
e 

10. Load, bearing Pressures & Footing Size
 D and L=loads (service) at the level of base of base of footing
 If eccentricity falls outside the kern distance
mb
3
P
2
q
b
m
3
P
2
q
o
max
max




a
max q
q 

11. Thank you