Analysis the Behavior of Multi layers Slabs Under Different Parametric Study

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.


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 Ø8/m) as shown in Fig.  1. 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.  columns with dimensions 15x15x30 cms. All slabs will be subjected to increment uniform load pressure.

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.  Ultimate Load SO S3 S2 S1

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

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]. 4. RESULTS AND DISCUSSION Considering the studied parameters of the present study, the following results were observed:

A. 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.

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/cm 2 .      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.

A. Ultimate Load
The ultimate loads for the studied slabs are shown in Table 8 and fig. 10.

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/cm 2 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 ,

A. Ultimate Load
The ultimate loads for the studied slabs are shown in Table 11    Ultimate Load SO S11 S10 S12 analytical analysis for tested group slabs So, S10, S11 and S12.      Load / Deflection Curve S10 S12 S0 S11