**Open Access**-
**Total Downloads**: 5 -
**Authors :**Mohamed Abou Elmaaty Amin, Mohamed Hussein, Mohamed Ahmed Ahmed -
**Paper ID :**IJERTV8IS020048 -
**Volume & Issue :**Volume 08, Issue 02 (February – 2019) -
**Published (First Online):**19-02-2019 -
**ISSN (Online) :**2278-0181 -
**Publisher Name :**IJERT -
**License:**This work is licensed under a Creative Commons Attribution 4.0 International License

#### Analysis the Behavior of Multi layers Slabs Under Different Parametric Study

Mohamed Abou Elmaaty Amin Assistant Professor of Structural Engineering Faculty of Engineering, Fayoum University

Fayoum, Egypt

Mohamed Hussein

Professor of Reinforced Concrete Faculty of Engineering, Zagazig University

Zagazig, Egypt

Mohamed Ahmed Ahmed

Assistant lecture,

Giza Engineering Institute,Ministry of Higher Education, Egypt Giza, Egypt

Abstract C

asting reinforced concrete elements in multi layers become a necessity in special types of structural elements such that flat slabs , raft and deep beams. Study of the behaviour of multi layers slabs under the effect of the applied loads due to different parametric study such as interface surface between layers, the location of layers in compression or tension zone as well as the effect of compressive strength of the different layers. The purpose of this research is to examine the effect of a previous parametric study on the behavior of simply supported slabs. A commercial non-linear finite element program, such as "ANSYS version 12"[1] was used to study the previous slabs. A comparison was made between the slab which was cast as one layer and to that slabs which were cast in multi layers with the different parametric study. the results which obtained from theortical modeling of multi layer slabs showed that the studied parametric has an important effect on the flexural behaviour of slabs.

Keywords: Nonlinear, finite element, multi layers, horizontal joints, flexural behavior slabs.

INTRODUCTION

The aim of this study is to study the behaviour of multi layers reinforced concrete slabs due to different parametric study. A numerical model was used to study such slabs. All codes of the specification or previous work [2] treatment the multi layered slabs (slabs with horizontal joints) by different ways such that ACI Code [3], British Standard: BS 8110 [4] , Australian Standard [5], Indian Standard: IS 456:1978 [6] and. Egyptian Code 2017 [7]. In the previous article [8] a comparison was made between the theoretical model and experimental model [9], the results show that the difference between experimental and theoretical analysis varies from (5% to 10%) for ultimate load and (1% to 10.5%) for deflection and (6.5% to 13%) for toughness [6]. According to the previous results the numerical models can be used to analyze the behaviour of multi layers slabs under different parametric study as the effect of change the compressive strength of the concrete layers, the location of horizontal joint and the effect of roughness between slab layers.

DESCRIPTION OF STUDIED SLABS

All slabs are simply supported by four columns with equal span (110.0X110.0 cm) and (8.0) cm in thickness with top and bottom mesh reinforcement will be (6 Ã˜8/m) as shown in Fig.

All slabs subjected to uniformly distributed load till failure

which is divided into many load steps. Each parametric study contains three slabs, table 1 summarized the description of the studied slabs.

Fig.1 Typical concrete dimensions and reinforcement details (All dimensions in cm)

Table1. Summarized the Description of the Studied Slabs

Parametric study

Slab

Slab DIM

(cm)

Slab RNFT TOP& BOTT.

No. of lay–

-er

Fcu (Kg/c m2)

Thickn-

-ess of two layer

Coeffic-

-ient of roughn-

-ess

Refere –

– nce s lab

S 0

110*110

*8

6 Ã˜ 8

/m/

1

300

Total thickne ss

—

110*110

0.5 ts at

Effect

S 1

*8

6 Ã˜ 8

/m/

2

300

top &botto

0.25

of

m

roughn-

110*110

0.5 ts at

– ess

S 2

*8

6 Ã˜ 8

/m/

2

300

top &botto

0.50

m

110*110

0.5 ts at

S 3

*8

6 Ã˜ 8

/m/

2

300

top &botto

0.75

m

110*110

200 at

0.5 ts at

Effect of

change

concrete s t rength ( Fc u) a t bottom

S 4

*8

6 Ã˜ 8

/m/

2

bott &300t op

top &botto m

0.75

S 5

110*110

*8

6 Ã˜ 8

/m/

2

250 at bott &300t op

0.5 ts at top

&botto m

0.75

S 6

110*110

*8

6 Ã˜ 8

/m/

2

300 at bott &300t

0.5 ts at top

&botto

0.75

op

m

110*110

300 at

0.5 ts at

Effect of

change

concrete s t rength ( Fc u) a t top

S 7

*8

6 Ã˜ 8

/m/

2

bott &200

top

top &botto m

0.75

S 8

110*110

*8

6 Ã˜ 8

/m/

2

300 at bott &250

top

0.5 ts at top

&botto m

0.75

S 9

110*110

*8

6 Ã˜ 8

/m/

2

300 at bott &300

0.5 ts at top

&botto

0.75

top

m

Effect of the

S 10

110*110

*8

6 Ã˜ 8

/m/

2

300

Tension zone

0.75

location of

S 11

110*110

*8

6 Ã˜ 8

/m/

2

300

Natural zone

0.75

hor izon-

– t a l

joint

S 12

110*110

*8

6 Ã˜ 8

/m/

2

300

Comp –

-ression zone

0.75

110*110

0.5 ts at

S 3

*8

6 Ã˜ 8

/m/

2

300

top &botto

0.75

m

110*110

200 at

0.5 ts at

Effect of

change

concrete s t rength ( Fc u) a t bottom

S 4

*8

6 Ã˜ 8

/m/

2

bott &300t op

top &botto m

0.75

S 5

110*110

*8

6 Ã˜ 8

/m/

2

250 at bott &300t op

0.5 ts at top

&botto m

0.75

S 6

110*110

*8

6 Ã˜ 8

/m/

2

300 at bott &300t

0.5 ts at top

&botto

0.75

op

m

110*110

300 at

0.5 ts at

Effect of

change

concrete s t rength ( Fc u) a t top

S 7

*8

6 Ã˜ 8

/m/

2

bott &200

top

top &botto m

0.75

S 8

110*110

*8

6 Ã˜ 8

/m/

2

300 at bott &250

top

0.5 ts at top

&botto m

0.75

S 9

110*110

*8

6 Ã˜ 8

/m/

2

300 at bott &300

0.5 ts at top

&botto

0.75

top

m

Effect of the

S 10

110*110

*8

6 Ã˜ 8

/m/

2

300

Tension zone

0.75

location of

S 11

110*110

*8

6 Ã˜ 8

/m/

2

300

Natural zone

0.75

hor izon-

– t a l

joint

S 12

110*110

*8

6 Ã˜ 8

/m/

2

300

Comp –

-ression zone

0.75

Mesh configuration

The mesh which used in the finite element model will be of size ranging from a minimum of 25x25x25 mm to a maximum of 50x50x50 mm. The finite element mesh is shown in Fig. 2.

DESCRIPTION OF FINITE ELEMENT MODEL FOR

STUDIED SLABS

According to the previous article [8], the utilized numerical models can be used to analysis the behavior of multi layers slabs under different parametric study. A finite element program (ANSYS V12) [1] was used to study the effect of horizontal construction joints on reinforced concrete flat slabs. Three-dimensional finite element models were developed to simulate the envelope response of the test slab specimens which listed in table 1. All slabs supported by four edge columns with dimensions 15x15x30 cms. All slabs will be subjected to increment uniform load pressure.

Fig.2 The finite element mesh

Model restraints

The details of Slab restrains are shown in Fig 3. The left side of the slab was restrained in the vertical direction and the horizontal direction ux , uy , uz. , while at the right side of the slab was restrained in vertical direction only.

Fig.3 The slab restrains

Loading scheme and loading increments

The slab was exposed to vertical pressure load located over the area on the upper face of the slab as shown in Fig.4. In (ANSYS) program the load can be applied in steps, each load step is divided to load increments. The solution requires the user to define a maximum number of iterations for each load increment. Within this number of iterations the solution will continue to the next load step if the out of balance forces are within a prescribed limit. The load on the slabs was gradually increased until failure occurred. The size of the load increments was chosen to achieve convergence and at the same time attains an acceptable level of accuracy. Small load increments usually lead to better accuracy and improved convergence with the penalty of more computational cost.

Fig.4 The slab loads

Material properties

The stress-strain relationships for concrete and reinforcing bars as well as all properties of such materials and the finite element models which were used to represent the material such as concrete (SOLID65), reinforcement bars (LINK 180) and supporting element (SOLID 185) were described in details in an article [8].

RESULTS AND DISCUSSION

Considering the studied parameters of the present study, the following results were observed:

Effect of roughness coefficient

All studied slabs So,S1,S2 and S3 for the same (Fcu) =300 Kg/cm2 , the horizontal joint is in mid thickness and friction

coefficient values were ( 0.25 , 0.50 , 0.75 ) for studied slabs S1,S2,S3 respectively .

Ultimate Load

The ultimate loads for the studied slabs are shown in Table 2 and fig. 5. The figure shows the comparison between the reference slab and the studied slabs due to the changing friction (roughness) coefficient.

Table 2. Effect of roughness coefficients on ultimate loads

Case of study

Slab name

Fcu (kg/cm2)

Friction coefficient

ultimate load ( ton )

Effect of roughness coefficient

So

300

1

11.37

S1

0.25

7.27

S2

0.50

8.43

S3

0.75

9.54

Ultimate Load

Ultimate Load

12

10

8

6

4

2

0

12

10

8

6

4

2

0

1

1

SO

S3

S2

S1

SO

S3

S2

S1

LOAD ( ton )

LOAD ( ton )

Fig. 4 Effect of roughness coefficent on the Ultimate load of the reference slab(So) and slabs ( S1,S2,S3 )

Load-Deflection Response

Table 3 displays the maximum deflection for the studied slabs (So,S1,S2,S3) due to the changing friction coefficient, while Fig. 5 shows the relation between load and deflection for the previous slabs under the same effect of the parametric study.

Case of study

Slab name

Fcu (kg/cm2)

Friction coefficient

Deflection ( mm )

Effect of roughness coefficient

So

300

1

11.3

S1

0.25

10.8

S2

0.50

12.9

S3

0.75

10.3

Case of study

Slab name

Fcu (kg/cm2)

Friction coefficient

Deflection ( mm )

Effect of roughness coefficient

So

300

1

11.3

S1

0.25

10.8

S2

0.50

12.9

S3

0.75

10.3

Table 3. Effect of roughness coefficients on maximum deflection

14.00

12.00

10.00

8.00

6.00

4.00

SO

S1

S2

S3

14.00

12.00

10.00

8.00

6.00

4.00

SO

S1

S2

S3

0.00

deflection ( mm )

15.00

0.00

deflection ( mm )

15.00

2.00

0.00

2.00

0.00

5.00

5.00

10.00

10.00

Load On Area ( n/mm2)

Load On Area ( n/mm2)

Fig. 5 Effect of roughness coefficent on the relation between Ultimate load and deflection of the reference slab(So) and slabs ( S1,S2,S3 )

Toughness

Toughness

50

40

30

20

10

0

1

SO S3 S2 S1

Toughness

50

40

30

20

10

0

1

SO S3 S2 S1

Area under load deflection

curve

Area under load deflection

curve

Flexural toughness or energy absorption is the term used to quantify the energy absorbing capability of concrete , it is the area under the load deflection curve of concrete in flexure up until a deflection equal to the span length divided by 150 [3]. Therefore the flexural toughness values for various slabs calculated at the designated deflection of 7 mm [3]. Fig. 6 and table 4 show the toughness which obtained from analytical analysis for the studied slabs.

Fig.6 Effect of roughness coefficent on the flexure toughness of the reference slab(So) and slabs ( S1,S2,S3 )

Table 4. Effect of roughness coefficients on maximum deflection

Effect of change concrete strength of bottom layer

All studied slabs So,S4,S5 and S6 for the same (Fcu) =300 Kg/cm2 in the top layer and difference in the bottom layer with values (200,250,300) Kg/cm2 for slabs S4,S5 and S6 respectively, friction coefficient will be constant and equall to

0.75 as well as the horizontal joint is in mid thickness for all slabs.

A. Ultimate Load

The ultimate loads for the studied slabs are shown in Table 5 and fig. 7. The figure shows the comparison between the reference slab and the studied slabs due to the changing of concrete strength for bottom layer from 200 to 300 kg/cm2.

Table 5. The effect of chang concrete strength for bottom layer on ultimate loads

Case of study

Slab name

Fcu (kg/cm2)

Friction coefficient

ultimate load ( ton )

Effect of

So

300

1

11.37

changing

S4

300 top

0.75

4.33

concrete

200 bott

strength

S5

300 top

4.59

of

250 bott

bottom

S6

300 top

9.54

layer

300 bott

Fig. 7 Effect of chang concrete strength of bottom layer on the Ultimate load of the reference slab(So) and slabs ( S4,S5,S6 )

Case of study

Slab name

Fcu (kg/cm2)

Friction coefficient

Toughness (T. mm )

Effect of

So

1

46.74

changing

S1

0.25

31.79

concrete strength

300

S2

0.50

34.9318

of bottom

laye

S3

0.75

41.72

Case of study

Slab name

Fcu (kg/cm2)

Friction coefficient

Toughness (T. mm )

Effect of

So

1

46.74

changing

S1

0.25

31.79

concrete strength

300

S2

0.50

34.9318

of bottom

laye

S3

0.75

41.72

B.Load- Deflection Response

Fig. 8 shows the relation between load and deflection of the studied slabs, while table 6 shows the maximum deflection for the studied slabs (So,S4,S5,S6) from analytical analysis .

Load / Deflection curve

14

12

load ( ton )

load ( ton )

10

4.3 Effect of change concrete strength on top layer

All studied slabs So,S7,S8 and S9 for the same (Fcu)

=300Kg/cm2 in bottom layer and difference in top layer with

So values (200,250,300) Kg/cm2 for studied slabs S7,S8 and S9

8 S6

6

S4

4

S5

2

0

0.00 5.00 10.00 15.00

deflection ( mm )

Fig. 8 Effect of chang concrete strength of bottom layer on the relation between load and deflection of the reference slab(So) and slabs ( S4,S5,S6 )

Table 6. Effect of chang concrete strength for bott. layer on max. deflection

Case of study

Slab name

Fcu (kg/cm2)

Friction coefficient

Deflection ( mm )

Effect of

So

300

1

11.37

changing

S4

300 top

0.75

1.9

concrete

200 bott

strength

S5

300 top

2.21

of

250 bott

bottom

S6

300 top

10.3

layer

300 top

C. Toughness

Area under load deflection curve

Area under load deflection curve

Fig. 9 and table 7 show the toughness which obtained from analytical analysis for tested group slabs So, S4, S5 and S6.

50

40

30

20

Toughness

50

40

30

20

Toughness

10

0

10

0

1

SO S6 S5 S4

1

SO S6 S5 S4

Fig. 9 Effect of chang concrete strength of bottom layer on toughness of the reference slab(So) and slabs ( S4,S5,S6 )

Case of study

Slab name

Fcu (kg/cm2)

Friction coefficient

Toughness (t.mm)

Effect of

So

300

1

46.74

changing

S4

300 top

0.75

6.4

concrete

200 bott

strength

S5

300 top

8.05

of

250 bott

bottom

S6

300 top

41.72

layer

300 bott

Case of study

Slab name

Fcu (kg/cm2)

Friction coefficient

Toughness (t.mm)

Effect of

So

300

1

46.74

changing

S4

300 top

0.75

6.4

concrete

200 bott

strength

S5

300 top

8.05

of

250 bott

bottom

S6

300 top

41.72

layer

300 bott

Table 7. Effect of chang concrete strength for bott. layer on toughness

respectively , friction coefficient will be constant and equall to

0.75 for all studied slabs and the horizontal joint is in mid thickness also in all slabs.

Ultimate Load

The ultimate loads for the studied slabs are shown in Table 8 and fig. 10. The figure show the comparison between the reference slab and the studied slabs due to the changing of concrete strength for bottom layer from 200 to 300 kg/cm2.

Table 8. Effect of chang concrete strength for top layer on ultimate loads

Case of study

Slab name

Fcu (kg/cm2)

Friction coefficient

ultimate load ( ton )

Effect of

So

300

1

11.37

changing

S7

300 bott

0.75

6.54

concrete

200 top

strength

S8

300 bott

7.82

of top

250 top

layer

S9

300 bott

9.54

300 top

Ultimate Load

12

10

8

6

4

2

0

1

SO S9 S7 S8

Ultimate Load

12

10

8

6

4

2

0

1

SO S9 S7 S8

LOAD ( ton )

LOAD ( ton )

Fig. 10 Effect of chang concrete strength of top layer on the Ultimate load of the reference slab(So) and slabs ( S7,S8,S9 )

Load-Deflection Response

Fig. 11 and table 9 show the relation between load-deflection relation and the maximum deflection respectively for the studied slabs (So,S7,S8,S9) as a result of analytical study.

14

12

10

8

6

4

2

0

0.00

Load / Deflection curve

So

S9

S7

S8

14

12

10

8

6

4

2

0

0.00

Load / Deflection curve

So

S9

S7

S8

5.00

5.00

deflection ( mm )

deflection ( mm )

10.00

10.00

15.00

15.00

load ( ton )

load ( ton )

Fig. 11 Effect of chang concrete strength of top layer on the load deflection relation of the reference slab(So) and slabs ( S7,S8,S9 )

Table 9. Effect of chang concrete strength for top layer on maximum deflection

Case of study

Slab name

Fcu (kg/cm2)

Friction coefficient

Deflection (mm)

Effect of

So

300

1

11.30

changing

S7

300 bott

0.75

4.31

concrete

200 top

strength

S8

300 bott

5.7

of top

250 top

layer

S9

300 bott

10.3

300 top

Toughness

Fig. 12 and table 10 show the toughness which obtained from analytical analysis for tested group slabs So, S7, S8 and S9.

4.4 Effect of change in location of horizontal joint

To investigate the effect of the location of the horizontal joint all studied slabs So,S10,S11 and S12 have the same (Fcu)

=300Kg/cm2 and the coefficient of roughness equall to 0.75 .

The location of horizontal joint was located in ( tension zone , neutral zone and compression zone) for studied slabs S10,S11 and S12 respectively ,

Ultimate Load

The ultimate loads for the studied slabs are shown in Table 11 and fig. 13. The figure shows the A comparison between the reference slab and the studied slabs due to the changing of concrete strength for bottom layer from 200 to 300 kg/cm2.

Table 11. Effect of changing horizontal joint location on ultimate loads

Case of study

Slab name

Horizontal joint location

ultimate load ( ton )

So

no

11.37

Effect of

S10

Compression zone

5.60

changing

horizontal

S11

Natural zone

9.54

joint

location

S12

Tension zone

4.53

Ultimate Load

12

10

8

6

4

2

0

1

SO S11 S10 S12

Ultimate Load

12

10

8

6

4

2

0

1

SO S11 S10 S12

Area under load deflection

curve

Area under load deflection

curve

Toughness

50

40

LOAD ( ton )

LOAD ( ton )

30

20

10

0

1

SO S9 S7 S8

Fig. 12 Effect of chang concrete strength of top layer on toughness of the reference slab(So) and slabs ( S7,S8,S9 )

Case of study

Slab name

Fcu (kg/cm2)

Friction coefficient

Toughness (t.mm)

Effect of

So

300

1

46.74

changing

S7

300 bott

0.75

19.41

concrete

200 top

strength

S8

300 bott

34.22

of top

250 top

layer

S9

300 bott

41.72

300 top

Case of study

Slab name

Fcu (kg/cm2)

Friction coefficient

Toughness (t.mm)

Effect of

So

300

1

46.74

changing

S7

300 bott

0.75

19.41

concrete

200 top

strength

S8

300 bott

34.22

of top

250 top

layer

S9

300 bott

41.72

300 top

Table 10 Effect of chang concrete strength of top layer on toughness

Fig. 13 Effect of changing horizontal joint location on the Ultimate load

Load-Deflection Response

Fig. 14 shows the relation between load and deflection of the slabs (So,S10,S11,S12) while table 10 show the maximum

deflection for the previous slabs due to the results which obtained from analytical analysis.

Load / Deflection Curve

Load / Deflection Curve

deflection ( mm )

deflection ( mm )

14

12

10

8

6

4

2

0

14

12

10

8

6

4

2

0

S10

S10

S12

S0

S11

0.00

S12

S0

S11

0.00

5.00

5.00

10.00

10.00

15.00

15.00

load ( ton )

load ( ton )

Fig. 14 Effect of changing horizontal joint location on the load deflection relation

Table 12. Effect of changing horizontal joint location on maximum deflection

Case of study

Slab name

Horizontal joint location

Deflection (mm)

So

no

11.30

Effect of

S10

Compression zone

2

changing

horizontal

S11

Natural zone

10.3

joint

location

S12

Tension zone

0.95

Toughness

Area under load deflection curve

Area under load deflection curve

Fig. 15 and table 13 show the toughness which obtained from analytical analysis for tested group slabs So, S10, S11 and S12.

Toughness

50

40

30

20

10

0

1

SO S11 S10 S12

Toughness

50

40

30

20

10

0

1

SO S11 S10 S12

Case of study

Slab name

Horizontal joint location

Toughness (t.mm )

So

no

46.74

Effect of

S10

Compression zone

3.98

changing

horizontal

S11

Natural zone

41.72

joint

location

S12

Tension zone

2.47

Case of study

Slab name

Horizontal joint location

Toughness (t.mm )

So

no

46.74

Effect of

S10

Compression zone

3.98

changing

horizontal

S11

Natural zone

41.72

joint

location

S12

Tension zone

2.47

Fig. 15 Effect of changing horizontal joint location on toughness Table 13 Effect of changing changing horizontal joint on toughness

CONCLUSIONS

According to the obtained results from the analytical study, the following conclusions can be drawn:

When the friction coefficient is increased between layers causes the increase in ultimate load.

At the same load as increasing in friction coefficient causes decreasing in deflection values.

As increasing friction coefficient between layers as increasing the toughness values of the studied slabs.

For a bottom layer when increasing concrete strength causes an increase in ultimate load.

Change in a concrete strength in the bottom layer causes early failure for the studied slab except if the two-layer has the same concrete strength.

Due to the previous conclusion the toughness and deflection decrease in comparison with reference slab and slab with multi layer which has the same concrete strength for both layer.

Changing the concrete strength of the top layer and keep the strength of bottom layer constant and higher than that for the top layer, it will give good performance for the flexure behaviour of the studied slabs.

When a horizontal construction joint located in tension zone it will be the worst case of the slabs for the flexural behaviour than if it located in the compression zone.

The best location for the horizontal joint in the natural zone (mid thickness) for the flexural behaviour.

REFERENCES

e-ISSN: 2278-1684,p-ISSN: 2320-334X, Volume 15, Issue 6 Ver. I (Nov. – Dec. 2018), PP 45-54

[9]. Metwally, I. M., and Issa, M. S., "Influence Of Horizontal Construction Joint On The Flexural Behavior Of Reinforced Concrete Slabs " HBRC Journal, Vol.3, No. 3 December 2007 pp (81-91).