1. Lecture 11 - 12: Foundations
AR362 - Structural Systems In Architecture IV
Lecture : Foundations
Res.Asst. Erkan DURMAZGEZER
Department of Civil Engineering
Izmir, TURKEY

2. FOUNDATIONS
In a structure, internal forces are transmitted from column members to foundations.
Force transmission is needed to perform safely.
Soil strength is much mure smaller than the column strength, consequently column
and shear wall members do not set into the soil directly. Stress generated by the
ground floor columns, plates (or beams) are positioned between the soil and ground
floor columns. Otherwise vertical (column or shear wall) members settle into the soil
which results structural damage in structure.
Independent from the type of superstructure, reinforced concrete foundations are preferred due to durability considerations and soil conditions.

3. Wall Footings (Duvar Altı Temel)
TYPES OF FOUNDATIONS
Wall Footings (Duvar Altı Temel)
Individual Footings (Tekil – Münferit Temel)
Combined Footings (Birleşik Temel)
Strip Foundation (Sürekli Temel)
a) One way strip foundation
b) Two way strip foundation
5) Mat (or Raft) Foundation (Radye Temel)
a) With Beam
b) Without Beam
6 ) Foundation on Piles (Kazıklı Temel)

4. Wall Footings (Duvar Altı Temel)
TYPES OF FOUNDATIONS
Wall Footings (Duvar Altı Temel)
Generally used in 1-2 storey masonry structures.
Common Dimensions
Width of the reinforced concrete foundation beam 50 – 70 cm
Height of the reinforced concrete beam 30 – 40 cm.

5. TYPES OF FOUNDATIONS
2) Individual Footings (Tekil Temel)

6. 2) Individual Footings (Tekil Temel)
TYPES OF FOUNDATIONS
2) Individual Footings (Tekil Temel)
Transverse beam elements are used to tie individual footings, enables to transfer earthquake forces effectively through the foundation system.
Width of the transverse beam members is at least 15cm.
Dimension of the footing is selected in such a way that stress transmission between the foundation to the soil is proceeded safely. Stress generated by the footing, should be less than the soil bearing capacity.
Not suitable for residential type of buildings due to the tendency to different settlement of column members.

7. 3) Combined Footing (Birleşik Temel)
TYPES OF FOUNDATIONS
3) Combined Footing (Birleşik Temel)
If distance between two columns are
close, combined footing is used.
Footing can be formed gradually wider,
where the level axial load is higher.

8. TYPES OF FOUNDATIONS
4a) One Way Strip Foundation (Bir Yönde Sürekli Temel)

9. 4a) One Way Strip Foundation (Bir Yönde Sürekli Temel)
TYPES OF FOUNDATIONS
4a) One Way Strip Foundation (Bir Yönde Sürekli Temel)
Height of the foundation footing is at least 30cm; whereas width is 100 cm.
Footing width is determined so as to stress generated by the footing is
less than the soil bearing capacity.
Not suitable for residential type of building since this type of foundation is only
suitable for structures that column directions in plan, are all the same.

10. TYPES OF FOUNDATIONS
4b) Two Way Strip Foundation (İki Yönde Sürekli Temel)

11. 4b) Two Way Strip Foundation (İki Yönde Sürekli Temel)
TYPES OF FOUNDATIONS
4b) Two Way Strip Foundation (İki Yönde Sürekli Temel)
Height of the foundation footing is at least 30cm; whereas width is 100 cm.
Footing width is determined so as to stress generated by the footing is
less than the soil bearing capacity.
Suitable for residential type of building. The risk of different settlement in columns
is relatively low, since members are tied in both direction.

12. 5) Mat or Raft Foundation (Radye Temel)
TYPES OF FOUNDATIONS
5) Mat or Raft Foundation (Radye Temel)
Mat Foundation without Beam:
Single large sized plate is formed beneath the column members.
This type of foundation is required when allowable soil pressure is low.
Is suitable to prevent the different column settlement.
Foundation slab thickness should be at least 30cm; whereas slab height in residential
buildings can be estimated by 10 x the number of of storeys, in cm.

13. TYPES OF FOUNDATIONS
5) Mat or Raft Foundation (Radye Temel)

14. 6) Pile Foundation (Kazıklı Temel)
TYPES OF FOUNDATIONS
6) Pile Foundation (Kazıklı Temel)
A pile is basically a long cylinder of a strong material such as concrete that is pushed into the ground to act as a steady support for structures built on top of it.
When there is a layer of weak soil at the surface. This layer cannot support the weight of the building, so the loads of the building have to bypass this layer and be transferred to the layer of stronger soil or rock that is below the weak layer.
When a building has very heavy, concentrated loads, such as in a high rise structure, bridge, or water tank.
Pile foundations are used in the following situations:

15. Transverse Beam Properties (Bağ Kirişlerin Özellikleri)
Minimum cross sectional dimension cannot be smaller than span between two column/30.
Values specified for design axial load in transverse beam in the first row, is the % of the column compressive load.
Example
Design the transverse beam.
Material C25 – S420.
Soil type D.

16. Transverse Beam Properties (Bağ Kirişlerin Özellikleri)
Solution
N = 0.12x2000 = 240 kN
Cross – section dimension should be at least 300mm x 300mm.
Longitudinal reinforcement is 4ϕ18. Area of longitudinal reinforcement = 1018 mm2
As required = N / 365 MPa = 657 mm2.
SATISFIED !!!

17. SOIL STRESS MODEL - DEFINITIONS
Nd = Column design load including G + Q load patterns.
h = Foundation depth.
σz = Soil stress formed beneath the foundation due to design load.
σzem = Soil stress capacity.
fzn = Soil net stress capacity.
γz = Soil density
γb = Concrete density = 25 kN/m3
Soil Stress = Stress due to Column Forces + Stress due to Foundation Concrete
- Stress Generated by Excavated Soil

18. SOIL STRESS MODEL - DEFINITIONS
Soil Stress = Stress due to Column Forces + Stress due to Foundation Concrete
- Stress Generated by Excavated Soil
σz γb h γz h < 1.5 σzem
σz (γb - γz ) h < 1.5 σzem where γb - γz = γ
σz < 1.5 σzem – γh
γ = 18 – 20 kN/m3
fzn = 1.5 σzem – γh (net soil strength)
Decide h and determine fzn so as to
σz < fzn

19. COMPUTATIONAL MODEL Nd2, Nd5, Nd8 = Column design loads (kN)
σz1, σz2, σz3 = Stress produced in soil by column forces (kN/m2)
q1= σz1b, q2= σz2b, q3= σz3b = Equivalent line stress produced by column design loads (kN/m).
In order to reduce the stress produced by column forces, one can extend the foundation beam
(a1 and a2).
Line stresses produced by design loads are in euilibrium with the line stresses q1, q2, q3.

20. COMPUTATIONAL MODEL
Column design forces are determined by analyzing the super structure.
q1, q2, q3 line stresses are evaluated numerically.
2) For each span, soil stress values are averaged for the sake of simplicity.

21. COMPUTATIONAL MODEL

22. COMPUTATIONAL MODEL Determination of Footing Width b:
Internal shear and moment affects in footing cantilever:

23. MOMENT AND SHEAR DIAGRAMS OF THE FOUNDATION BEAM
Foundation beam can be extent in order to reduce the soil stress, but the length of the cantilever cannot be exceeded 1.5m.
Foundation beam height is determined so as to carry at least %80 of shear generated by the superstructure. The remaining shear effect can be carried by shear reinforcement.
In bending reinforcement calculations, section is T in span region whereas section in support is rectangular.
Minimum amount of longitudinal reinforcement is enough in most cases, since height of the section is assigned
generously.
As1 and As2 reinforcement are evaluated from the moment diagram shown above.

24. CALCULATION STEPS Cantilever length a1 and a2 is selected.
Foundation beam width bw is selected.
Foundation footing height is selected.
Clear cover is selected.
Height of the foundation is evaluated based on the foundation without shear reinforcement should carry at least %80 of the shear.
Foundation footing width is evaluated.
Foundation shear reinforcement is evaluated if required.
Soil stress is determined.
Longitudinal reinforcements are evaluated.
Additional reinforcements are assigned in support region, if it is required.
Footing plated thickness ‘t’ is controlled.
Footing reinforcements is evaluated.
Beam reinforcements are drawn.

25. STRIP FOUNDATION IN ONE WAY
EXAMPLE
One way foundation will be formed beneath the 30 cm x 60 cm columns. Column design forces are shown in figure. Perform the required analysis for foundation so as to carry the design forces safely. Land contour is specified as 1.4m from the left of the column and 3 meter from the right of the column.
Soil load carrying capacity is σzem = 150 kN /m2 . Materials used C25 – S420.
fcd = MPa
fctd = 1.2 MPa,
fyd = fywd = 365 MPa
min ρ = 0.8 fctd / fyd =
max ρ = 0.02
max (ρ – ρ’) = 0.85 ρb =

26. STRIP FOUNDATION IN ONE WAY
EXAMPLE
Foundation beam width bw is selected as 50 cm. Foundation footing height t = 30 cm. Concrete cover is 5cm.
Determination of height of the foundation beam h :
Shear should be carried by foundation beam, but in that case foundation size is not economical. Height of the foundation is evaluated based on the foundation without shear reinforcement should carry at least %80 of the shear.

27. STRIP FOUNDATION IN ONE WAY
EXAMPLE
Determination of foundation footing width b :

28. STRIP FOUNDATION IN ONE WAY
EXAMPLE

29. STRIP FOUNDATION IN ONE WAY
Longitudinal Reinforcement:
Minimum amount of longitudinal reinforcement is enough in most cases, since height of the section is assigned generously. Calculation will be performed according to maximum bending moment.
Span B - C:
Md = kNm, d = 100 – 5 = 95 cm = 950 mm
Table Solution (for T beam since it is dealed with span region).

30. STRIP FOUNDATION IN ONE WAY
Longitudinal Reinforcement:
Minimum amount of longitudinal reinforcement is enough in most cases, since height of the section is assigned generously. Calculation will be performed according to maximum bending moment.
Span B - C:
Md = kNm, d = 100 – 5 = 95 cm = 950 mm
Table Solution (for T beam since it is dealed with span region).
b / bw = 3 (but table is formed only for specific ratio – 4 is used
t /d = 30/95 = ~ 0.3
Kfcd = 1500 x 9502 / [178.1(106)] x 16.67] = (much more above from the entry at the top)
Means that minimum amount of reinforcement is enough.

31. STRIP FOUNDATION IN ONE WAY
Longitudinal Reinforcement:
Minimum amount of longitudinal reinforcement is enough in most cases, since height of the section is assigned generously. Calculation will be performed according to maximum bending moment.
Span A - B:
Md = 99.8 kNm, d = 100 – 5 = 95 cm = 950 mm
Minimum amount of reinforcement is enough.

32. STRIP FOUNDATION IN ONE WAY
Longitudinal Reinforcement:
Minimum amount of longitudinal reinforcement is enough in most cases, since height of the section is assigned generously. Calculation will be performed according to maximum bending moment.
Support C and Support A: Maximum moment is kNm
Md = kNm, d = 100 – 5 = 95 cm = 950 mm
Table Solution (for rectangular beam since it is dealed with support region – table is at next slide).
Means that minimum amount of reinforcement is enough (cannot be read at the table).
As min = x500x950 = 1235 mm2
As available = = 1055 mm2
As add required = 1235 – 1055 = 180 mm2 (1ϕ16 added).
Support B
Additional reinforcement is not required.
As min = x500x950 = 1235 mm2 < Aavailable = 2 x = 1658 mm2
Mid – Layer Reinforcement is required throughout the foundation beam since height of the beam is more than 60 cm.
As min = x500x950 = 475 mm2 (2ϕ12 added at midlevel).

33. STRIP FOUNDATION IN ONE WAY
Longitudinal Reinforcement:

34. STRIP FOUNDATION IN ONE WAY
Drawing: