How to design a pile cap

1. DESIGN OF PILE CAP
NARULA INSTITUTE OF TECHNOLOGY
DEPT. OF CIVIL ENGINEERING

2. GROUP MEMBERS
1. SHABAN AKHTAR (12701312085)
2. AYON BHATTACHARJEE (12701312025)
3. ANUPAM GHOSH (12701312012)
4. SOURAV GHOSH (12701312098)
5. SAMRAN BANERJEE (12701312078)
6. SANAT BANIK (12701312079)

3. INTRODUCTION
• Foundations provide support for structures,
transferring their load to layers of soil or rock that
have sufficient bearing capacity and suitable
settlement characteristics.
• Very broadly, foundations can be categorised as
shallow foundations or deep foundations.
• Shallow foundations are typically used where the
loads imposed by a structure are low relative to the
bearing capacity of the surface soils.
• Deep foundations are necessary where the bearing
capacity of the surface soils is insufficient to support
loads imposed and so they are transferred to deeper
layers with higher bearing capacity.

4. WHAT IS A PILE CAP?
• A pile cap is a thick concrete mat that rests on concrete
or timber piles that have been driven into soft or
unstable ground to provide a suitable stable foundation.
• It usually forms part of the foundation of a building,
typically a multi-story building, structure or support
base for heavy equipment.
• The cast concrete pile cap distributes the load of the
building into the piles.
• A similar structure to a pile cap is a "raft", which is a
concrete foundation floor resting directly onto soft soil
which may be liable to subsidence.

5. NEED FOR PILE CAP
• Pile foundation is required when the soil bearing
capacity is not sufficient for the structure to withstand.
This is due to the soil condition or the order of bottom
layers, type of loads on foundations, conditions at site
and operational conditions.
• A pile foundation consists of two components: Pile cap
and single or group of piles. Piles transfers the loads
from structures to the hard strata, rocks or soil with
high bearing capacity. These are long and slender
members whose length can be more than 15m.

6. DESIGN OF PILE CAP
• As per IS 2911 (Part I/ Sec 3) -2010, the pile cap
may be designed by assuming
• that the load from column is dispersed at 45° from
the top of the cap up to the mid
• depth of the pile cap from the base of the column
or pedestal. The reaction from
• piles may also be taken to be distributed at 45°
from the edge of the pile, up to the
• mid depth of the pile cap. On this basis the
maximum bending moment and shear
• forces should be worked out at critical sections.

7. ASSUMPTIONS INVOLVED
• (i) Pile cap is perfectly rigid.
• (ii) Pile heads are hinged to the pile cap and
hence no bending moment is
• transmitted to piles from pile caps.
• (iii) Since the piles are short and elastic columns,
the deformations and stress distribution are
planer.

8. DESIGN PARAMETERS
• (i) Shape of pile cap.
• (ii) Depth of pile cap.
• (iii) Amount of steel to be provided.
• (iv) Arrangement of reinforcement.

9. DESIGN PROCEDURE
• DETERMINE NUMBER OF PILE
• PILE CAP ARRANGEMENT AND PLANE DIMENSION
• PILE CAP PRELIMINARY DEPTH
• CHECK FORCES IN PILES
• CHECK FOR PUNCHING SHEAR
• CHECK FOR SHEAR
• DESIGN OF MOMENT
• CHECK FOR BOND
• DETAILS FOR REINFORCEMENT

10. Explanation of pile cap design with example:-
EXAMPLE 1 :-
Diameter of pile : 300 mm
Spacing between the piles : 3xd= 3x400 mm [ As per IS 2911
= 1200 mm (Part 1/Sec 3) :2010
Clause :
6.6.2.]
No of piles under a pile cap: 3
Size of column : 400x400 mm
Load transferred by column : 1500 kN
Load on each pile : 1500/3= 500 kN
The dimension of the pile cap, the distance between the connecting line of
the piles and the face of critical zone of punching shear are given in the
figure with details………..

11. Details about the pile cap of this example……………..

12. We
have
assume
that the
effectiv
e depth
of pile
cap
is 500
mm……
…

13. Unit Moment at face AB = 0.287x1000= 287 kN-m
Unit Moment at face AC = 0.287x1000= 287 kN-m
Unit Moment at face BC = 0.1x1000= 100 kN-m
Formula used to calculate Area of steel against
corresponding moment:
Mu= 0.87 x fy x As t x d (1 - 0.42 x Xu/d)
(AS PER IS:456 (2000) ANNEX G , CLAUSE
38.1………
Mu = Moment
fy = Characteristic strength of steel, here 415
As t = Area of steel
d= Effective depth of pile cap
Xu= Depth of neutral axis

14. Area of steel required parallel to AB = 1991 mm2
Area of steel required parallel to AC = 1991 mm2
Area of steel required parallel to BC = 693 mm2
We should provide 12 mm rod of 113 mm2
Spacing through AB = (113 x 1000)/1991= 60 mm
Spacing through AC = (113 x 1000)/1991= 60 mm
Spacing through BC = (113 x 1000)/693= 160 mm
OVERALL DEPTH OF THE PILE CAP =(500+(100+12+12+6)X2)= 760 mm

15. Explanation of pile cap design with example:-
EXAMPLE 2 :-
Diameter of pile : 300 mm
Spacing between the piles : 3xd= 3x400 mm [ As per IS 2911
= 1200 mm (Part 1/Sec
3) : 2010
Clause : 6.6.2.]
No of piles under a pile cap: 4
Size of column : 400x400 mm
Load transferred by column : 1600 kN
Load on each pile : 1600/4= 400 kN
The dimension of the pile cap, the distance between the
connecting line of the piles and the face of critical zone of
punching shear are given in the figure with details………..

16. Details about the pile cap of this example……………..

17. We have
assume
that the
overall
depth of
pile cap
is 600
mm……
…

18. Unit Moment at face AB = 0.23x800= 184 kN-m
Unit Moment at face BC = 0.23x800= 184 kN-m
Unit Moment at face CD = 0.23x800= 184 kN-m
Unit Moment at face DA = 0.23x800= 184 kN-m
Formula used to calculate Area of steel against
corresponding moment:
Mu= 0.87 x fy x As t x d (1 - 0.42 x Xu/d)
(AS PER IS:456 (2000) ANNEX G , CLAUSE 38.1………)
Mu = Moment
fy = Characteristic strength of steel, here 415
As t = Area of steel
d= Effective depth of pile cap
Xu= Depth of neutral axis

19. Area of steel required parallel to AB = 1877 mm2
Area of steel required parallel to BC = 1877 mm2
Area of steel required parallel to CD = 1877mm2
Area of steel required parallel to DA= 1877mm2
We should provide 12 mm rod of 113 mm2
Spacing through AB = (113 x 1000)/1877= 60 mm
Spacing through BC = (113 x 1000)/1877= 60 mm
Spacing through CD = (113 x 1000)/1877= 160 mm
Spacing through DA = (113 x 1000)/1877= 160 mm
EFFECTIVE DEPTH OF THE PILE CAP =(600-(100+12+12+6)X2)= 340
mm

20. Making of PILE CAP
In practical field…………

21. ACKNOWLEDGEMENT:
■ Our project is successful due to the effort of those people
who have given their valuable time and advice. We sincerely
appreciate the inspiration, support and guidance of all those
people .
We, the student of "NARULA INSTITUTE OF TECHNOLOGY" are
extremely thankful to our teachers for giving us the
opportunity to do this project on the topic of ”Design of Pile
Cap”. At this juncture we feel deeply honour in expressing
our sincere thanks to Dr.Chandrasekhar Sen Majumdar, Prof.
Abhipriya Halder, Prof.Priyabrata Guha sir
for making the resources available at right time and
providing valuable insights leading to the successful
completion of our project.

22. CONCLUSION
A pile cap is a thick concrete mat that
rests on concrete or timber piles that
have been driven into soft or unstable
ground to provide a suitable stable
foundation. It usually forms part of
the foundation of a building, typically a
multi-story building, structure or support
base for heavy equipment. The
cast concrete pile cap distributes the
load of the building into the piles. A
similar structure to a pile cap is a "raft",
which is a concrete foundation floor
resting directly onto soft soil which may
be liable to subsidence.

23. SPECIAL THANKS to
PROF. ABHIPRIYAHALDER
We are very thankful that we have a
teacher cum leader like you. Your inspiration
really motivate us to do this project on such
a topic which play a valuable role in civil engineering.
Without your inspiration it is impossible to complete
this project. Thanks a lot sir……….for your support and
inspiration………………