10. A P P E N D I X 2 - S T R U C T U R A L D E S I G N O F A P I L E

10.1. Code requirements

This chapter discuss an example for Structural design o f a reinforced concrete pile.

The design o f a pile is discussed in several codes and the proposed requirements for

the design are varies in each code. Table 10.1 summarizes the requirements o f BS

8004, BS 5400 - P 4 and BS 8110.

A t present, specific references in U K codes to the design o f reinforcement in piles is

limited to two documents, BS 8004:1986 "Foundations" and B D 32/88 "Piled

Foundations". A summary o f the requirements o f these codes is given below:

i . BS 8004: 1986 "Foundations"

a) Vertical piles which are axially loaded need not be designed as structural

columns unless part o f the pile extends above ground level (C17.3.3.3). For this

latter case, only the upper portion o f the pile need be considered as a column

down to a point o f f ixi ty.

b) A l l forces acting on the pile are to be determined and the pile reinforced

accordingly (C17.3.3.4, CI 7.3.3.6, and C17.4.4.3.2). Some or all o f the pile

length may be unreinforced (CI 7.4.4.3.2). Pre-cast concrete piles are to be

designed to BS 8110 (or CP 116).

c) Where tensile forces are to be resisted by the pile, adequate reinforcement is

required to resist the entire tension stresses. The reinforcement should be

provided for the foil length o f the pile or where tensile forces are small, to a

depth at which the tensile forces have been folly transmitted to the ground (CI

7.3.3.7 and CI 7.4.5.3.2).

d) Min imum spacing o f links is given as 150mm (CI 7.4.4.4.2).

e) For raking piles, loads may be considered as axial wi th an applied bending

force at the top (CI 7.3.3.5).

f) Durability and protection o f reinforcement against corrosion is provided by

dense impermeable concrete free from defects (CI 10.4.7). Nominal cover for

various exposure conditions should be as BS 8110.

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i i . Standard B D 32/88: 1988 "Piled Foundations"

a) This standard applies to both the design o f driven and bored piles (CI 2.1).

b) Pile caps are to be designed to BS 8004 but CI 3.1 states that the structural

design o f all concrete elements o f the pile is to be to BS 5400 Pt 4. ^

BS 8110 states that embedded piles need not be designed as columns and piles carrying

axial load only need not be reinforced. Some rules are provided regarding calculation

o f axial forces which may be accommodated without reinforcement but no guidance

is given on calculation o f shear capacity. Where reinforcement is required, BS 8110 is

mentioned for design but is not specifically invoked, except for pre-cast piles. No

guidance is given for curtailment o f longitudinal steel. ' *

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Code/Standard (Date)

Cover to Reinforcement

Longitudinal Reinforcement Transverse Reinforcement Crack Control Max Crack

Width

Code/Standard (Date)

Cover to Reinforcement

M i n . No

M i n . Dia.

Max. Spacing

M i n %

Max. Spacing

M i n . Diameter

Crack Control Max Crack

Width

BS 8110 Pt 1 (1985)

75mm (Concrete cast against ground)

4 (Rectangular) 6 (Circular)

12mm Tension 0.8% (Steel) 0.45% (high yield)

12 times Smallest Main bar size

- times 4 Largest main Bar size or 6mm

Only checked i f N < 0.2fcuAc Then max. width = 0.3mm

BS 5400 Pt 1 (1990)

45mm (Buried C30 Concrete)

4 (Rectangular) 6 (Circular)

12mm 300mm l % o r 0.15Nfy

12 times Smallest Main bar Or 0.74 times effective depth

- times 4 Largest main Bar size

0.25mm (Buried concrete) 0.1mm i f groundwater p H < 4 . 5

BS 8004 As BS8110 But add 40mm for concrete cast against ground

As BS 8110 A s B S 8110—- Not mentioned

Table. 10-1 Summary of Code Requirements (Page 123 and Page 124)

Code/Standard (Date)

Permissible Stresses Maximum Axial Load Code/Standard (Date) Concrete Steel Without Reinforcement With Reinforcement

BS8110 Pt 1 (1985)

Compression

0 . 6 7 ^ Ym

Shear Ve+0.6'^-^- ' '

fy/

(Tension & Compression) 0.4 feu A c

0.4 feu Ae + 0.75 A e

fy

BS 5400 P t4 (1990)

Compression

0.67=^ Ym

Shear 0.5. f^u ; • (Triangular Stress Distribution)

0.38 feu (Uniform Stress Distribution)

Compression fy 1 (Km + / y / 2 0 0 0 )

Tension 0.4 feu . b. dc 0.4 feu. b. de + fyc. A ' Si + fs2. As2

BS 8004 (1986)

A s B S 8110 A s B S 8110 A s B S 8110 A s B S 8110

Ae - area o f concrete A ' si - area o f compression As2 - area o f r / f in

other face Asc - area o f vertical reinf. material

b - width o f section

do - depth of concrete in compression feu - characteristic concrete cube strength fs2 - stress in reinf in other face fy - characteristic strength o f reinforcement h - overall depth o f section

M - applied design moment N - applied designed axial load V - applied design shear Vc - design concrete shear stress Yfn - partial safety factor for strength o f

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Global Reinforcement Design Requirements

BS8004 BS8110 BD 32/88 (BS5400 Pt 4)

o Axial Compression

No guidance Refer to BS8110

Detailed design rules for structural design (See Table 3.1.1)

Detailed design rules for structural design (See Table 3.1.1)

o Axial Tension General guidance given on length of pile to be reinforced

-do- -do-

o Flexure No guidance Refer to BS 8110

-do- -do-

o Shear No guidance Refer to BS 8110

- do- - do-

o Buckling Check for Buckling i f Co<20kN/m2

No checks required No checks required

Rules for:

o Minimum Reinforcement

No minimum reinforcement required

-do- -do-

o Links Minimum spacing 150mm

-do- -do-

o Calculation of Rebar

RefertoBSS 110. Only upper part of pile above ground level to be designed as a column

-do- -do-

o Cover AsBSSllOplus 40mm 75mm (Concrete cast against ground)

45mm max +40mm in accordance with BS8004 cl 2.4.5

o Crack Control Not mentioned Only required for N<0.2fou

0.1mm to 0.25mm depending on exposure conditions

o Durability Some guidance given Detailed requirements for concrete design and nominal cover to reinforcement

Detailed requirements for concrete design and nominal cover to reinforcement

Table 10-2: Summary o f Current U K Design Codes

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