 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): 19022019
 ISSN (Online) : 22780181
 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 nonlinear 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. Threedimensional 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 stressstrain 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 )

LoadDeflection 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 )

LoadDeflection Response
Fig. 11 and table 9 show the relation between loaddeflection 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

LoadDeflection 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 twolayer 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

eISSN: 22781684,pISSN: 2320334X, Volume 15, Issue 6 Ver. I (Nov. – Dec. 2018), PP 4554
[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 (8191).