Seminar Report DESIGN AND COMPARISION OF FLAT SLAB USING IS 456-2000 AND ACI 318-08

7/27/2019 Seminar Report DESIGN AND COMPARISION OF FLAT SLAB USING IS 456-2000 AND ACI 318-08

1/33

A

SEMINAR REPORT ON

DESIGN AND COMPARISION OF FLAT SLAB USING IS 456-2000

AND ACI 318-08

BY

TUSHAR M. MADAMWAR

(ID-11001063)

GUIDED BY

Dr. K. N. KADAM

Department of Applied Mechanics

Government College of Engineering, Amravati.

(An Autonomous Institute of Government of Maharashtra)

2014-2015


2/33

CERTIFICATE

This is to certify that the seminar Report entitled DESIGN AND

COMPARISION OF FLAT SLAB USING IS 456-2000 AND ACI 318-08 submitted

by TUSHAR MANOJ MADAMWAR under my supervision and guidanceas a record of

the work carried outrby him, is accepted as the seminar report submission. It is submitted in

the partial fulfillment of the prescribed syllabus of Final Year Civil Engineering in

Government College of Engineering, Amravati For the academic year 2014 - 2015

Date :

DR. K. N. KADAM PROF. D. J. CHAUDHARI

Guide Head of Department

Applied Mechanics Department Applied Mechanics Department

Government College of Engineering, Government College of Engineering,

Amravati Amravati


3/33

DECLARATION

I hereby declare that the seminar entitled DESIGN AND COMPARISION OF

FLAT SLAB USING IS 456-2000 AND ACI 318-08 has beenexclusively carried out

and written by me under the guidance of Dr. K. N. Kadam , Assistant Professor, Department

of Applied Mechanics, Government College Of Engineering, Amravati for the course

Seminar. This work has not been previously formed the basis for the award of any degree or

diploma or certificate nor has been submitted elsewhere for the award of any degree or

diploma.

Place: Amravati TUSHAR MANOJ MADAMWAR

Date: (11001063)


4/33

ACKNOWLEDGEMENT

It gives me great pleasure in bringing out the seminar entitled " DESIGN AND

COMPARISION OF FLAT SLAB USING IS 456-2000 AND ACI 318-08". I express

my deep sense of gratitude and sincere regards to my respected guide Dr. K. N. Kadam.

Her timely guidance and friendly discussion had helped me immensely in selecting this

topic and completing the seminar work.

I would like to thank our Head of Department Prof. D. J. Chaudhari for

providing all facilities at the right period of time and for allowing me to deliver this

seminar.

I would also like to thank Dr. W. Z. Gandhare Principal, Government College

of Engineering, Amravati for providing all the facilities.

Last but not least, this acknowledgement would be incomplete without any

rendering impartial gratitude to all those person who have helped me directly or

indirectly in preparing this seminar report.

TUSHAR MANOJ MADAMWAR

(11001063)


5/33

TABLE OF CONTENTS

Chapter No. Title of Content Page No

Certificate

Declaration

AcknowledgementTable of contents

List of figures and tables

1 INTRODUCTION

1.1 Basic definition of flat slab

1.2 Components of flat slab

2 Advantages of flat slab

3 DESIGN OF FLAT SLAB USING IS 456-2000

3.1 components of flat slab design

3.2 Division into column and middle stripalong:

3.3 Drops

3.4 column Heads

3.5 Depth of flat slab

3.6 Estimation of load acting on slab

3.7 Total design moment on span

3.8 Negative and positive design moments

3.9 Effective depth of slab

3.10 Thickness of drop from maximumvemoment consideration

3.11 Shear in Flat Slab

4 DESIGN OF FLAT SLAB USING ACI 318-08

4.1 Drop of flat slabs

4.2 Thickness of the slab

4.3 Design strips

4.4 column head

4.5 Total factored static moment for a span

4.6 Shear provisions4.7 Numerical Example

5 RESULTS-CODAL COMPARISIONS

6 CONCLUSIONS

REFERENCES


6/33

LIST OF FIGURES

Fig. No Name of figure Page No

1.1 Flat slab with drop panel & column head

1.2conventional and beam free slab

LIST OF TABLES

Table

No

Name of table Page No

3.1 Drop dimensions

3.2 Column head dimensions

3.3 Depth consideration

3.4 Total design load3.5 Sum ofve and +ve moments

4.1 Minimum thickness of slab

4.2 Factored moment in column strip

4.3 Factored moment in column strip


7/33

ABSTRACT

Flat slabs system of construction is one in which the beams used in the

conventional methods of constructions are done away with. The slab directly rests on the

column and load from the slab is directly transferred to the columns and then to thefoundation. To support heavy loads the thickness of slab near the support with the

column is increased and these are called drops, or columns are generally provided with

enlarged heads called column heads or capitals. Absence of beam gives a plain ceiling,

thus giving better architectural appearance and also less vulnerability in case of fire than

in usual cases where beams are used.

Plain ceiling diffuses light better, easier to construct and requires cheaper form

work. As per local conditions and availability of materials different countries have

adopted different methods for design of flat slabs and given their guidelines in their

respective codes. The aim of this seminar is to try and illustrate the methods used for flat

slab design using ACI-318 and IS: 456 design codes.

For carrying out this project an interior panel of a flat slab with dimensions 6.6 x 5.6 m

and super imposed load 7.75 kN /m2was designed using the codes given above.


8/33

CHAPTER 1

INTRODUCTION

1.1

Basic definition of flat slab:In general, normal frame construction utilizes columns, slabs & beams. However it

may be possible to undertake construction without providing beams, in such a case the

frame system would consist of slab and column without beams. These types of slabs are

called flat slab, since their behavior resembles the bending of flat plates.(Fig 1.1 shows a

typical flat slab with its components)

1.2 Components of flat slabs:

i. Drops: Drops increases the shear strength of slab against punching shear failure.It

increases the negative moment carrying capacity of slab and stiffens it reducing the

defections.

ii. Column heads: Certain amount of negative moment is transferred from the slab to the

column at the support. To resist this negative moment the area at the support needs to be

increased .This is facilitated by providing column capital/heads. column heads increase

shear strength of slab.

Fig. 1.1 Flat slab with drop panel & column head


9/33

CHAPTER 2

ADVANTAGES OF FLAT SLAB

Flat slab has a number of advantages as compared to convenient slab beamsystem. These advantages are listed below.

i. Flexibility in room layout:Flat slabs allows to introduce partition walls anywhere

required, it allows the choice of omittion of false ceiling and finished soffit of slab

with skim coating.It also allows the owner to change the size of room layout.

ii. Saving in building height: Lower storey height will reduce building weight due to

lower partitions and cladding resulting in reduction of foundation load.

Approximately saves 10% in vertical members.

(refer Fig no 1.2)

Fig, 1.2 conventional and beam free slab

iii. Shorter construction time: Flat plates design facilitates the use of the big table

formwork to increase productivity.

iv. Ease of installation of M & E services: All M & E services can be mounted

directly on the underside of the slab instead of bending them to avoid the beams.

Avoid hacking through beams

v. Pre-fabricated welded mesh: Pre-fabricated welded mesh are available in standard

sizes, these mesh minimizes the installation time & helps in better quality control.


10/33

Chapter 3

Literature review


11/33

CHAPTER 3

DESIGN OF FLAT SLABS USING IS 456-2000

The term flat slab means a reinforced concrete slab with or without drops,supported generally without beams, by columns with or without flared column heads (see

Fig. 1.1). A flat slab may be solid slab or may have recesses formed on the soffit so that

the soffit comprises a series of ribs in two directions. The recesses may be formed by

removable or permanent filler blocks.

3.1 Components of flat slab design:

a)Column strip :Column strip means a design strip having a width of 0.25 l2, but not

greater than 0.25l1, on each side of the column centre-line, where l2 is the span in the

direction moments are being determined, measured centre to centre of supports and l1is

the span transverse to l2, measured centre to centre of supports.

b)Middle strip :Middle strip means a design strip bounded on each of its opposite sides

by the column strip.

c)Panel: Panel means that part of a slab bounded on-each of its four sides by the centre -

line of a column or centre-lines of adjacent-spans.

Table No Division into column and middle strip

Longer span Shorter span

L1 =6.6 m , L2=5.6 m

( i ) column strip

= 0.25L2= 1.4 m

But not greater than 0.25 L1= 1.65 m

(ii) Middle strip

= 5.6(1.4+1.4) = 2.8 m

L1=5.6 m , L2=6.6 m

( i ) column strip

= 0.25L2= 1.65 m

But not greater than 0.25L1= 1.4 m

(ii) Middle strip

= 6.6(1.4+1.4) = 3.8 m


12/33

Fig no.Dimensions of slab along longer and shorter span

3.3 DropsAs per clause 31.2.2 of IS 456-2000, the drops when provided shall be rectangular in plan

and have a length in each direction not less than one- third of the panel length in that

direction. For exterior panels, the width of drops at right angles to the non- continuous

edge and measured from the centre -line of the columns shall be equal to one half the

width of drop for interior panels.

Since the span is large it is desirable to provide drop

Table 3.1 Drop dimensions

Large span Short span

L1=6.6 m , L2=5.6 m

Not less than L1/3 = 2.2 m

L1=5.6 m , L2 =6.6 m

Not less thanL1/3 = 1.866 m

provide drop of size 2.2 x 2.2 m i.e. in column strip width.

3.4 Column Head

As per clause 31.2.3 of IS 456-2000,where column heads are provided, that portion of a

column head which lies within the largest right circular cone or pyramid that has a vertex

angle of and can be included entirely within the outlines of the column and thecolumn head, shall be considered for design purposes.

1.4 m

C.S

3.8 m

M.S

C.S 1.4 m

2.8 m

M.S

1.4 m

1.4 m M.S

5.6 m 6.6 m


13/33

Table 3.2 Column head dimension along:


L1=6.6 m , L2 =5.6 m

Not greater than L1/4 = 1.65 m

L1=5.6 m ,L2=6.6 m

Not greater than L1/4 = 1.4 mAdopting the diameter of column head = 1.30 m =1300 mm

3.5 Depth of Flat Slab

As per clause 23.2.1 of IS 456-2000, the thickness of the flat slab up to spans of 10 m

shall be generally controlled by considerations of span ( L ) to effective depth ( d ) ratios

given as below

Cantilever 7; simply supported 20; Continuous 26

For slabs with drops, span to effective depth ratios given above shall be applied directly;

otherwise the span to effective depth ratios in accordance with above shall be multiplied

by 0.9. For this purpose, the longer span of the panel shall be considered. The minimum

thickness of slab shall be 125 mm.

Table 3.3 Depth consideration


L =6.6 m , L2=5.6 m

= Say 260 mm

L =5.6 m ,L2=6.6 m

Say 220 mm

Taking effective depth of 25mm

Overall depth D = 260 +25 = 285 mm 125 mm (minimum slab thickness as per IS: 456)

It is safe to provide depth of 285 mm.

3.6 Estimation of Load Acting on The Slab:

Dead load acting on the slab = 0.285 x 25 = 6.25KN /m2=Wd1

Floor finishes etc. load on slab = 1.45KN /m2= Wd2


14/33

The Live load on slab = 7.75KN /m2= W1

Total dead load = Wd1+ Wd2=7.7KN /m2= Wd

Design live load shall not exceed three times the design dead load.

Check=: OKTotal design load =Wll+Wd=15.45 KN/m

2

3.7 Total Design Moment On Span (31.3.1)As per clause 31.3.1 of IS 456-2000, the absolute sum of the positive and average and is

given by negative bending moments in each direction shall be taken as

Mo=

Mo=total moment

W = design load on an area l1l2

ln = clear span extending from face to face of columns, capitals, brackets or walls, but not

less than 0.65 l1

l1= length of span in the direction of Mo.

l2= length of span transverse to l1 .

Circular supports shall be treated as square supports having the same area.

Equivalent side of the column head having the same area:

A= =

Clear span along long span =ln =6.6-(1.152)-(1.152)=5.448 >4.29

(Should not be less than 0.65 l1) ok

Clear span along long span =ln =5.6-(1.152)-(1.152)=4.44 >3.64

(Should not be less than 0.65 l1) ok


15/33

Table 3.4 Total design load


l n=5.448 m , l2=5.6 m

W w l 2l n

W 15.45 5.6 5.448 471.36kN

l n=4.44 m , l2=6.6 m

W w l2 ln

W 1 5 . 4 5 6 . 6 4 . 4 4 452.74k N

Table 3.5 The absolute sum of negative and positive moment in a panel


ln=5.448 m , l2=5.6 m

Mo= ln=4.44 m , l2=6.6 m

Mo= 3.8 Negative and Positive Design Moments

As per clause 31.4.3 of IS 456-2000 ,the negative design moment shall be at the

face of rectangular supports, circular supports being treated as square supports having the

same columns built integrally with the slab system area. Shall be designed to-resist

moments arising from loads.

In an interior span, the total design moment Mo shall be distributed in the following

proportions

Negative design moment 0.65

Positive design moment 0.35

In an end span, the total design moment Mo shall be distributed in the following

proportions

Interior negative design moment: Positive design moment:


16/33

Exterior negative design moment:

acIs the ratio of flexural stiffness of the exterior columns to the flexural stiffness of the

slab at a joint taken in the direction moments are being determined and is given by:

ac=

K c=sum of the flexural stiffness of the columns meeting at the joint.

Ks=flexural stiffness of the slab, expressed as moment per unit rotation.

It shall be permissible to modify these design moments by up to 10 percent, so long as the

total design moment Mo for the panel in the direction considered is not less than that

required by:

Mo= The negative moment section shall be designed to resist the larger of the two interior

negative design moments determined for the spans framing into a common support unless

an analysis is made to distribute the unbalanced moment in accordance with the stiffness

of the adjoining parts.

Moments In Column Strip

As per clause 31.4.5 of IS 456-2000,

1.Negative moment at an interior support: At an interior support, the column strip shall

be designed to resist 75 percent of the total negative moment in the panel at that support.

2.Negative moment at an exterior support:

a) At an exterior support, the column strip shall be designed to resist the total negative

moment in the panel at that support.

b) Where the exterior support consists of a column or a wall extending for a distance

equal to or greater than three-quarters of the value of l2. The length of span transverse to

the direction moments are being determined, the exterior negative moment shall be

considered to be uniformly distributed across the length l2 .

3.Positive moment for each span:For each span, the column strip shall be designed to

resist 60 percent of the total positive moment in the panel.


17/33

Moments in The Middle Strip

a)That portion of-the design moment not resisted by the column strip shall be assigned to

the adjacent middle strips.

b) Each middle strip shall be proportioned to resist the sum of the moments assigned to

its two half middle strips. The middle strip adjacent and parallel to an edge supported by

a wall shall be proportioned, to resist twice the moment assigned to half the middle strip

corresponding to the first row of interior columns.

Stiffness Calculation

As per clause 31.5.2.1 of IS 456-2000,

let the height of the floor = 4.0 m

clear height of the column = height of floor depth of dropthickness of slabthickness

of head.

= 4000140285300 = 3275 mm

Effective height of column = 0.8 x 3275 = 2620 mm

(Assuming one end hinged and other end fixed)

stiffness coefficient= ac =

1.longer span

kc= bottom + top =2

=

ks , ac From table 17 of IS: 456-2000 & acminac

acmin o k

Hence the correction for pattern loading in the direction of short span is not required.


18/33

3.9 Distrubution Of Bending Moment Across The Panel Width

As per clause 31.4.3.3 of IS 456-2000,

In an exterior panel.

Longer span

1.column strip

Negative B.M at exterior support = Positive span BM = Negative span BM at interior support =

-166.5 kNm2.Middle Strip

Negative BM at exterior support = Positive span BM =

Negative BM at interior support =

3.10 Effective depth of the slab

Thickness of the slab, from consideration of maximum positive moment any where in the

slab.

Maximum +ve BM occurs in the column strip (long span) = 90.91 kNm

factored moment = 1.50 x 90.91 = 136.36 kNm

Mo0.138fck


19/33

d= d=132.83 mm 140 mmUsing 12 mm

(diameter) main bars.

Overall thickness of slab =14015+ 161 mm 170 mmDepth (along longitudinal direction) =170-15-

Depth (along longitudinal direction) = 150-12=138mm

3.11 Thickness of drop from maximum negative moment consideration

Thickness of drop from consideration of maximumve moment anywhere in the panel.

Max negative BM occurs in the column strip = 166.6 KNm

Mu=fckbd2

1.5=0.138 d=254.3mm

Say 260 mm. Use 12 mm barsOver all thickness of flat slab:D=260+15+

3.12 Shear in Flat Slab

As per clause 31.6 of IS 456-2000, the critical section for shear shall be at a distance d/2

from the periphery of thecolumn/capital/ drop panel, perpendicular to the plane of the

slab where d is the effective depth of the section The shape in plan is geometrically

similar to the supportimmediately below the slab.

Check for shear stress developed in slab

The critical section for shear for the slab will be at a distance d/2 from the face of drop.

Perimeter of critical section =4 340=9340mmVo=1.5 [ ]=729.78kNNominal shear stress =Tv= shear strength of concrete =Tc=0.25==1.1N/Permissible shear stress =Tv Ks=(0.5+) ,c=0.848Ks=1.348


20/33

Tv


21/33

CHAPTER 4

DESIGN OF FLAT SLAB USING ACI 318-08

4.1 Drop of flat slabs

As per clause 13.2.5 of ACI 318-08, where a drop panel is used to reduce

amount of negative moment reinforcement over the column of a flat slab, size of drop

panel shall be in accordance with the following:

Drop panel shall extend in each direction from centerline of support a distance not less

than one-sixth the span length measured from center -to center of supports in that

direction. Projection of drop panel below the slab shall be at least one -quarter the slab

thickness beyond the drop. In computing required slab reinforcement, thickness of drop

panel below the slab shall not be assumed greater than one-quarter the distance from edge

of drop panel to edge of column or column capital.

4.2 Thickness of the slab

As per clause 9.5.3 of ACI 318-08, for slabs without interior beams spanning

between the supports and having a ratio of long to short span not greater than 2, the

minimum thickness shall be in accordance with the provisions of Table below and shall

not be less than the following values:

(a) Slabs without drop panels as ......................... 5 in.(b) Slabs with drop panels as defined.................. 4 in.

Table 4.1 Minimum Thickness of Slabs Without Interior Beams


22/33

consider the slab to be designed with drops

Depth of the slab from deflection criteria = (the yield strees fyi=60,000psi,

4.3 Design strips: (13.2.1)

Column strip is a design strip with a width on each side of a column centerline equal to

0.25 l2or 0.25 l1,whichever is less.

Middle strip is a design strip bounded by two column strips.

A panel is bounded by column, beam, or wall centerlines on all sides.

4.4 Column head

The upper supporting part of a column is enlarged to form the column head. The diameteror the column head is made 0.20 to 0.25 of the span length.

4.5 Total factored static moment for a span: (13.6.2)

Total factored static moment for a span shall be determined in a strip bounded laterally

by centerline of panel on each side of centerline of supports.

Absolute sum of positive and average negative factored moments in each direction shall

not be less than.

Mo=

Wu=load per unit area acting on the slab panel

ln=Clear spanlnshall extend from face to face of columns, capitals, brackets, or walls.

Value of lnshall not be less than 0.65l1. Circular or regular polygon shaped supports

shall betreated as square supports with the same area.

l2=When the span adjacent and parallel to an edge is being considered, the distance from

edge to panel centerline shall be substituted for l2.

In an interior span, total static momentMo shall be distributed as follows:

Negative factored moment .................................0.65

Positive factored moment ...................................0.35


23/33

In an end span, total factored static moment 0M shall be distributed as follows:

Negative moment sections shall be designed to resist the larger of the two interiornegative factored moments determined for spans framing into a common support unless

an analysis is made to distribute the unbalanced moment in accordance with stiff nesses

of adjoining elements. Edge beams or edges of slab shall be proportioned to resist in

torsion their share of exterior negative factored moments

Factored moments in middle strips:(13.6.6.3)

That portion of negative and positive factored moments not resisted by column

strips shall be proportionately assigned to corresponding half middle strips.

Each middle strip shall be proportioned to resist the sum of the moments assigned to its

two half middle strips.

A middle strip adjacent to and parallel with an edge supported by a wall shall be

proportioned to resist twice the moment assigned to the half middle strip corresponding

to the first row of interior supports.

Factored moments in column strips: (13.6.4)

Column strips shall be proportioned to resist the following portions in percent of

exterior negative factored moments:


24/33

Table 4.2

Column strips shall be proportioned to resist the following portions in percent of exterior

negative factored moments:

Tables 4.3

Modification of factored moment:

Modification of negative and positive factored moments by 10 percent shall be

permitted ,provided the total static moment for a panel in the direction considered is not

less than that required by Mo=

4.6 Shear provision(punching shear): (13.6.8)

Two-way action where each of the critical sections to be investigated shall be

located so that its perimeter bois a minimum but need not approach closer than d / 2 to

(a) Edges or corners of columns, concentrated loads, or reaction areas, or

(b) Changes in slab thickness such as edges of capitals or drop panels.

Nominal shear strength of concrete:

For flat slabs Vc=nominal shear strength of concreteVcShall be smallest of the

following: [Where cis the ratio of long side to short side of the column, concentrated

load or reaction area and where asis 40 for interior columns, 30 for edge columns,20 for

corner columns]

Vc==


25/33

Vc== Vc=4


26/33

4.7 Numerical example:

consider the slab to be designed with drops

Depth of the slab from deflection criteria =

Minimum depth of slab

=max( )

=max(5.58in,4.74in)

=5.58in

6 in > 4 in (for slabs with drop panels)

Providing a slab of thickness 6 in or 152.4 mm.

Density of concrete =150 lb/

Dead load on the slab = Live load on the slab = 161.80 psf = 7.75 kN /m

2

Design load on the slab = (1.2 x 7.5 + 1.6 x 161.80)

= 348.88 350 psf

= 16. 765 kN /m2

For short span direction, the total static design moment :

Mo=

ft-kips=201.04kNm

This is distributed as follows :

Negative design moment = 148.06 x 0.65 = 96.24 ft -kips = 130.50 kNm

Positive design moment = 148.06 x 0.35 = 51.891 ft -kips = 70.36 kNm

The column strip has a width of 2 x2 With

=0 (no beams)Bending moment for column strip:

Negative moment for column strip = 75 % of total negative moment in the panel

= 0.75 x 96.24 = 72.18 ft -kips = 97.88 kNm

Positive moment for column strip = 60 % of total positive moment in the panel.

= 0.60 x 51.891 = 31.135 ft -kips = 42.21 kNm


27/33

Static moment along longer direction

Mo=

This is distributed as follows:

Negative design moment = 237 x 0. 65 = 154 ft-kips = 208.89 kNmPositive design moment = 237 x 0.35 = 83.00 ft -kips = 113.22 kNm

The column strip has a width of 2 With

= Bending moment for column strip

Negative moment for column strip = 75 % of total negative moment in the pannel

= 0.75 x 154.00 = 115.50 ft -kips = 157.66 kNm

Positive moment for column strip = 60 % of total positive moment in the panel.

= 0.60 x 83.00 = 49.8 ft -kips = 67.977 kNm

Bending moment for middle strip along shorter span

Negative moment for middle strip = 0.25 x 96.24

= 24.06 ft-kips

= 32.84 kNm

positive moment for middle strip = 0.40 x 51.891

= 20.7564 ft-kips= 28.33 kNm

Bending moment for middle strip along longer span

Negative moment for middle strip = 0.25 x 154 = 38.5 ft -kip

= 52.55 kNm

Positive moment for middle strip = 0.40 x 83.00 = 33.2 ft kips

= 45.318 kNm

Max moment (+ve orve ) along shorter span = 72.18 ft -kips

Max moment (+ve orve) along longer span = 115.50 ftkips

Pmax=maximum permitted reinforcement ratio

Mu=P Mu=* +


28/33

=

=3.07in=77.79mm

provide a slab of thickness 6 in.

Drop in flat slabs:

Span of panel in longer direction = 16.76 ft

length of drop panel

=

=5.58ft

With half width on either side of th e centre line of support = 0.85 m

Thickness of drop = Check for punching shear:

Vu= factored shear, acting at distance d/2 from face of the support.

(assuming column of size 400 mm by 400 mm)

Vu=350[ ]=350[]=82265.365 lb=365.91kN

= The nominal stress of concrete will be smallest of the following :

(a)Vc== (b)Vc== (c) Vc =4

Vc> Vu section safe in punching shear safe.


29/33

Reinforcement detail

Depth=6 ft,Width=16.76 ft

Minimum area of steel required = 0.0018 x gross area of concrete

(for control of temperature & shrinkage cracking)

=0.0018 In 14.22 ft direction,Pmin=

In 16.76 ft direction,Pmin=

R=pfy( )psi or R= 1. Calculation of area of steelalong shorter span:

For negative moment in column strip:

R==150.933

Reinforcement ratio = 0.0040

Area of reinforcement = 0.0040 x 14.76 x 6 x 12 = 4.250 in2/ft

For positive moment in column strip :

R= =65


Area of reinforcement = 0.0017x 14.76 x 6 x 12 =1.8066 in2/ft

For negative moment in middle strip:R==50.311


Area of reinforcement = 0.0013x 14.76 x 6 x 12 = 1.38 in2/ft

For positive moment in middle strip:

R=

=43.40


Area of reinforcement = 0.00075x 14.76 x 6 x 12 = 0.79 in2/ft


30/33

2.Calculation of area of steel along longer span:

For negative moment in column strip:

R=

=219.77

Reinforcement ratio = 0.00375Area of reinforcement = 0.00375 x 16.22 x 6 x 12 = 4.38 in

2/ft

For positive moment in column strip :

R= =94.76


Area of reinforcement = 0.00175 x 16.22 x 6 x 12 = 2.04 in2/ft

For negative moment in middle strip:

R= =73.25Reinforcement ratio = 0.00125

Area of reinforcement = 0.00125x 16.22 x 6 x 12 = 1.4598 in2

/ft

For positive moment in middle strip:

R= =63.17


Area of reinforcement = 0.00115x 16.22 x 6 x 12 = 1.34 in2

/ft


31/33

CHAPTER 5

RESULTS-CODAL COMPARISIONS

CODE IS 456 -2000 ACI 318-08

Shape of test specimen

for concrete strength

(mm)

Cube

150x150x150

Cylinder

152.4x304.8

Grade of

concrete(N/mm)

20 20

Grade of steel (N/mm) 415 413.7

Negative moment

(KN-m)

188.5 208.89

Positive moments

(KN-m)

90 113.22

Area of

reinforcement(mm)

4290 2829

Thickness of slab for

Serviceability

criteria(mm)

170 150

Punching shear Safe Safe


32/33

CHAPTER 6

CONCLUSIONS

1.

By comparing with different codes we concluded that ACI 318 codeis more effective in designing of flat slabs.

2. As per Indian code we are using cube strength but in internationalstandards cylindered are used which gives higher strength than cube.

3.

Drops are important criteria in increasing the shear strength of the

slab.4.

Enhance resistance to punching failure at the junction of concrete

slab & column.

5. By incorporating heads in slab, we are increasing rigidity of slab.6.

In the interior span, the total design moments (Mo) are same for IS

456-2000 & ACI 318-08.7. The negative moments section shall be designed to resist the larger

of the two interior negative design moments for the span framing intocommon supports.

8. According to Indian standard (IS 456) for RCC code hasrecommended characteristic strength of concrete as 20, 25, and 30

and above 30 for high strength concrete. For design purpose strength

of concrete is taken as 2/3 of actual strength this is to compensate the

difference between cube strength and actual strength of concrete in

structure. After that we apply factor of safety of 1.5. So in practiceIndian standard actually uses 46% of total concrete characteristicstrength. While in International practice is to take 85% of total

strength achieved by test and then apply factor of safety which is

same as Indian standard. So in actual they use 57% of total strength.9.

Pre fabricated sections to be integrated into the design for ease of

construction.


33/33

CHAPTER 7

REFERENCES

1. Bureau of Indian Standards, New Delhi, IS 456:2000, Plain and Reinforced

Concrete - Code of Practice, Fourth Revision, July (2000).

2. American Concrete Institute, ACI 318-08, Building Code Requirements for

Structural Concrete and Commentary, January (2008).

3. Dr. V. L. Shaha & Dr. S. R. Karve Limit State Theory and Design of

Reinforced Concrete Sixth edition

4. Amit A. Sathwane , R. S. Deoalate (IJERA)Analysis and Design of Flat Slab and

Grid Slab and Their cost omparision

Seminar Report DESIGN AND COMPARISION OF FLAT SLAB USING IS 456-2000 AND ACI 318-08

Documents

Transcript of Seminar Report DESIGN AND COMPARISION OF FLAT SLAB USING IS 456-2000 AND ACI 318-08