DESIGN OF PILE CAPNARULA INSTITUTE OF TECHNOLOGY

DEPT. OF CIVIL ENGINEERING

GROUP MEMBERS1. SHABAN AKHTAR (12701312085)

2. AYON BHATTACHARJEE (12701312025)

3. ANUPAM GHOSH (12701312012)

4. SOURAV GHOSH (12701312098)

5. SAMRAN BANERJEE (12701312078)

6. SANAT BANIK (12701312079)

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.

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.

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.

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.

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.

DESIGN PARAMETERS• (i) Shape of pile cap.

• (ii) Depth of pile cap.

• (iii) Amount of steel to be provided.

• (iv) Arrangement of reinforcement.  

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

Explanation of pile cap design with example:-

EXAMPLE 1 :-Diameter of pile : 300 mmSpacing 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: 3Size of column : 400x400 mmLoad transferred by column : 1500 kNLoad 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………..

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

We have

assume that the effective depth of pile cap

is 500 mm……

…

Unit Moment at face AB = 0.287x1000= 287 kN-mUnit Moment at face AC = 0.287x1000= 287 kN-mUnit Moment at face BC = 0.1x1000= 100 kN-mFormula 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 = Momentfy = Characteristic strength of steel, here 415

As t = Area of steeld= Effective depth of pile cap

Xu= Depth of neutral axis

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 mmOVERALL DEPTH OF THE PILE CAP

=(500+(100+12+12+6)X2)= 760 mm

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: 4Size of column : 400x400 mm

Load transferred by column : 1600 kNLoad 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………..

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

We have assume that the overall

depth of pile cap

is 600 mm……

…

Unit Moment at face AB = 0.23x800= 184 kN-mUnit Moment at face BC = 0.23x800= 184 kN-mUnit Moment at face CD = 0.23x800= 184 kN-mUnit 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 = Momentfy = Characteristic strength of steel, here 415

As t = Area of steeld= Effective depth of pile cap

Xu= Depth of neutral axis

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 mmSpacing through BC = (113 x 1000)/1877= 60 mm

Spacing through CD = (113 x 1000)/1877= 160 mmSpacing through DA = (113 x 1000)/1877= 160 mm

EFFECTIVE DEPTH OF THE PILE CAP =(600-(100+12+12+6)X2)= 340 mm

Making of PILE CAPIn practical field…………

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.

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.

SPECIAL THANKS to PROF. ABHIPRIYA HALDER

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………………