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HDB Punching Shear Reinforcement

Halfen technical helpline:01932 5711664

Calculation method

Design

The design a nd layout of t he HDB system is

based on BS 8110 and uses technical reports

and test data to adapt the standard from

reinforcement links as specified, t o t he HDB

proprietary double headed stud system.

The ca lculat ion checks the shea r stress on

successive perimeters radiating from t he

column face perimeter, with shear stud

reinforcement provided a s required. The first

perimeter is checked at 1.5d from the face of

the column with subsequent perimeters at

0.75d spacings, until v < vc after w hich no

shear stud reinforcement is req uired.

Punching shear load (piercing load)

The Halfen calculation d isc allow s the user to

input the design load in tw o w ays

Veff = the design effective shear, which should

include the effect of any moment transferred

to the column, or

Vt = design shear transferred to t he column,

w hich is then multiplied by the appropriat e

factor for moment transfer, dependent on thecolumn type as shown below

Using Vt the program defa ults to the fo llowing

simplified multiplication facto rs, w hich in the

absence of calculation will be satisfactory to

use for braced structures with approximately

equal spans and approximately equal loading

to all spans surrounding the column.

Interior column: 1.15

Corner column: 1.25 (BS 8110 cl. 3.7.6)

Edg e column : 1.40

These simplified fa ctors may be cha nged if

more rigorous analysis is carried out.

Design concrete shear stress, vc (BS 8110 table 3.8)

vc = 0.79 100 As1/3 400 1/4 fcv

1/3

1.25 bv d d 25

where

100 As /(bv d) : reinforcement ratio, As: area of tension reinforcement

d: effective depth

bv: width of slab under consideration

fcv: characteristic strength of concrete

Perimeters

The perimeters used in the ca lculat ion have

radius corners rather than the rectangular

perimeters given in BS 8110,

For rectangular column

u1 = 2 (a+ b) + 2 (1.5d)

Calculation of shear stress

The shea r stress (v0) at the column face (u0

perimeter) is first checked to ensure it doesnot exceed vma x , if v0 > vmax then the

concrete slab and/or column should be

redesigned.

v0 = Veffu0d

vmax = 0.8 fcu or 5.6N/mm2

where fcu 50 N/mm2

The next check on the shea r stress is carried

out at the first perimeter (u1), 1.5d from

column face.

v1 = Veffu1d

If v1 < vc then no shear studs are required. If

v1 > v c shear studs are provided based on the

follow ing equations

vc v 2.2vc Asv = (1.57v vc) ud0.95 fy

minimum st ud reinforcement

Asv = 0.4 ud0.95 fy

where

fy = 500 N/mm2Asv = cross sectional area of shear studs

At the first and subsequent perimeters v islimited t o 2vc. If v exceeds this value then the

concrete slab and/or the column should be

redesigned v 2vc

The f irst pe rimeter is critical in deciding the

size and arrang ement of studs to be used. The

length of the stud arm is determined by the

perimeter where v = vc after w hich no more

studs are required.

The prog ram w ill auto mat ically select the

appropriate number and diameter of shear

studs, however the user can select different

sizes and arrangements to rationalise the

design.

Detailing

The prog ram a utoma tically checks the

geometry of t he shear stud arrangement to

ensure the following requirements are met.

The first stud is placed bet w een 0.35d

and 0.375d from the fa ce of t he column.

Subsequent studs are placed at centres

0.75d. The exa ct spacings a re

dependent on the particular HDB unit

selected.

The maximum tang ential spacing o f the

second studs is 1.7d.

The a bsolute ma ximum tang ential spacing

of a ny studs is 4d, how ever this can be

less depending on the reinforcement ratio,

effective depth and type of column.

b

1.5d

a

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5Halfen technical helpline:01932 571166

Increased shear strength: membrane action

For internal columns where 1.0%increased shear strength is available due to

membrane action with v up to 2.2vc. However

the absolute maximum tangential spacing of

any studs is reduced to 1.5d therefore this

option may only be viable for highly loaded

columns.

Halfen calculation software

Halfen software is available for the calculation

of punching shear reinforcement in concrete

flat slabs.

E6E5 E7 E8 G3 G4 G5

A12A8

D5

B10 B14 B18

D7 D8D6 F3 F4 F5

A16 A20

C8 C10 C12 C14 C16

Typical arrangements of HDB elements/arms

The Halfen comput er program ena bles you to

determine the optimum shear head

reinforcement needed, based on the following

inputs:

Column type

Relevant dimensions, eg thickness and

effective depth of the slab, and cross

sectional area of the column

Applied punching load (kN)

Concrete g rade Reinforcement ratio and concrete cover.

This calculat ion softw are is ava ilab le on

CD-ROM.

System requirements:

486 rated PC or higher

Window s 95, 98, ME, NT, 2000 XP

VGA monitor resolution 800 x 600 or

higher

Printer (optional: installed driver

necessary)