1. FOOTING

2. Footing -  A base (in or on the ground) that will support the structure.
A masonry section, usually concrete, in a rectangular form wider than the bottom of the foundation wall or pier it supports.
- The base or bottom of a foundation pier, wall, or column that is usually wider than the upper portion of the foundation. The added width at the bottom spreads the load over a wider area.

3. TYPES OF FOOTINGS
Footing requirements are generally covered in the building code and sized in accordance with the bearing capacity of the soil and the weight of the building. In areas subject to seasonal frost, the bottom of the footing must be placed below the frost line to prevent damage to the footing and structure due to frost heave. Typical footing types include:
spot footings
continuous spread footing
grade beam footing

5. Problem 1:
A 150 mm wall is carrying a total load of 150 kN per meter length of wall. Design a wall footing using the following:
fc’= 20 Mpa
fs = 140 Mpa
n = 9
R = 1.45 Mpa
j = 0.878
v = 0.50 Mpa
u = 2.2 Mpa
Allowable soil pressure = 75 kPa

6. Solution: Consider 1m length of wall;
Assume wt. of footing = 0.09(150) = kN
Total load = = kN
Req’d. Area = = m² 75
L(1) =
Net soil pressure = = kN m

7. Determine depth of footing:
from bending
M = (1.025) (1.025) 2
M = kN · m
d = mm

8. from shear
V = (1.025 – d) kN
Use d = 160 mm
v = V
Total depth = = 235 mm bd
0.40 = 68.2(1.025 – d) (1000)
Check wt. of footing
(1000) (d) (1000)
wt. of footing = (2.2) (0.235) (1) (2.4)
= – d
= kN < 13.5 kN
d = m
d = mm

9. A reinforcement; Deck bond stress: As = M fs jd
Spacing = 314 (1000) = 172 mm
1822
As = (1000)²
140 (0.878) (160)
= 20 mm bars 170 mm o.c.
As = 1822 mm²
Deck bond stress:
u = V
 jd
V = 68.2 (1.025) = kN
 =  (20) (1000) = 370 mm
170
u = (1000) = MPa < 2.2 MPa (ok)
370 (0.878) (160)

10. temp. bars
Ast = (2200) (235)
Ast = 1034 mm²
For 12 mm bars
A =  (12) ² = 113 mm ²
Use 10 – 12mm bars

11. Problem 2:
Design a square footing for a spiral column having a diameter of 678 mm carrying an axial load of 1780 kN.
Allow. soil bearing
pressure = 240 kPa
fc' = 17.5 MPa
fs = 138 MPa
n = 12
k =
j =
= 0.17
R = 1.38
u = 10.14
v = 0.09 D

12. Solution:
Assume wt. footing = 6% of 1780
wt. footing = 0.06 (1780)
wt. footing = Kn
Total load = = kN
Required area = = 7.86m²
L² = 7.86
L = m
Net upward soil pressure = = N/ m²
Try x
A = 2.82 (2.82)
Note: Change the round column into a square section
 A = 7.95 m²

13. (678)² = D²
D = 600 mm
M = (2.82) (1.11) (1.11) 2
d = 316 mm (Add mm approx.)
Try d = 490 mm

14. Check for beam shear:
V = q (c-d) L
V = ( ) (2.82)
V = N
ν =
2820 (490)
ν = 0.28 MPa
va = 0.09
va = 0.38 MPa > (safe)

15. Check for Punching shear:
Vp = q [L² - (d+a)²]
Vp = [(2.82)² - (1.09)²]
Vp =
vp = Vp Ap
Ap = 490 (1090) (4)
Ap =
vp =
va = 0.17
vp = MPa
va = 0.71 MPa > (safe)

16. (to compensate for bond stress)
Compute the steel requirements:
Check for Bond stress:
 =  (28) (13)
 = 1144 mm
As = 6650 mm²
Using 28 mm Ø bars:
(28)² n = 6650
n = say 13 bars
(to compensate for bond stress)

17. check wt. of footing:
Total depth = (1.5)
= 607 mm
wt. = (2.82) (2400) (9.81) (2.82)
wt. = N
check the area required:
A =
A = m² < m²
(our trial area is bigger
than the required area)
V = (1.11) (2.82)
V = N
u = 1.43 MPa
ua = 1.51 MPa
> (safe)

18. Foundation – the interfacing element between the superstructure and the underlying soil or rock.
Foundation Engineering – art and science of applying engineering judgment and the principles of soil mechanics to solve the interfacing problem
Retaining Structure – structure whose purpose is to retain a soil or other similar mass in a geometric shape other than occurring naturally under the influence of gravity
S = total ultimate settlement
S = Si + Sc + Ss
Si = immediate settlement resulting from the constant volume distortion of the loaded soil mass
Sc = consolidation settlement resulting from the time dependent flow of water from the loaded area under the influence of the load generated excess pore pressure which is itself dissipated by the flow
Ss = secondary settlement or creep which is also the dependent but may occur at essentially constant effective stress

19. Typical Foundation Types are:
Foundation for building (shallow/deep)
Foundations for smoke stacks, radio and television towers, etc. (s or d)
Foundations for port or Marine structures (maybe s or d, w/ extensive low or deep)
Foundation elements support open cuts or retain earth masses or bridge abutments (retaining structures)

20. Problems encountered in foundation designs
What constitutes satisfactory and tolerable settlements?
How variable is the soil Profile, and has client seen willing to authorize an adequate exploration program?
Can be the building be supported by the underlying soil on spread footing, mats, piles?
What is the likehood of a lawsuit if the foundation does not perform adequately?
Is money available for the foundation portion of the construction?
What is the ability of the local construction force?
What is the engineering ability of the foundation engineer?

21. General Requirements of Foundations
Depth must be adequate to avoid lateral expulsion of materials from beneath the foundation, particularly footing and mats.
Depth must be below seasonal volume changes such as freezing and thawing or the zone of organic materials
System must be safe against overturning, rotation, sliding, or soil rupture
System must be safe due to harmful materials present in soil
System should be adequate to sustain some changes be major in scope
The foundation should be economical in terms of the method of installation
Total earth movements and differential movements should be tolerable for the foundation element and or any superstructure elements

22. Soil Mechanics Engineering study of soil to obtain properties such as:
Engineering study of soil to obtain properties such as:
Strength Parameters
Compressibility Indexes
Permeability
Gravimetric – volumetric data (unit, weight, specific gravity, void ratio)   
This makes possible engineering Predictions and estimates of:
Bearing Capacity
Settlements
-amount
-rate
Earth Pressures
Pore Pressures and Dewatering quantities
The foundations engineer is concerned with the construction of some type of engineering structure of the earth great effort is required to separate the particles

23. Earth – composed of rock and soil
Rock – naturally occurring materials composed of mineral, particles so firmly bonded together that relatively
Soil – naturally occurring materials minerals particles which are fairly readily separated into relatively small pieces and in which the mass may certain air, water, or organic materials in varying accounts
Attenberg Limits – laboratory tests for arbitrary moisture contents to determine when the soil is on the verge of being viscious liquid (liquid limit) or nonplastic
Plastic Index – water content beyond which no further reduction of mass, volume takes place with additional moisture loss
Specific Gravity – may be determined in a laboratory test with moderate difficulty

24. Soil Classification Terms
Bedrock – rock its native location, usually extending greatly both horizontally and vertically
Boulders – smaller pieces of materials which have broken away from bedrock (10-12 in)
Gravel – common term used to describe pieces of rock from about 6 in. max. to less than ¼ in min. size
Sand – mineral particles ranging size from 0.05 to mm max to to mm
Clay – mineral particles smaller than silt size

25. SPT N value Relative density 0-4 very loose 4-10 loose
SPT N value Relative density
0-4 very loose
4-10 loose
medium dense
dense
50 very dense