Comparison of Structural Behaviour of Flat Plate System and Flat Slab

System for Reinforced Concrete Building

Nyan Phone 1#, Phyoe Hnin Thu Htun 2#
1#2#
Department of Civil Engineering
1#
Technological University (Thanlyin)
2#
Technological University (Hpa-an)
nyanphone.civil@gmail.com
phyohninthu82@gmail.com

Abstract— In recent years, flat plate building and flat structural behaviour of RC building with different slab
slab building constructions have been more popular in systems are analysed and compared by using software aids
Myanmar and it has been instead of conventional slab such as ETABS, SAFE, SAP 2000 and STAAD PRO etc.
system. The flat plate and flat slab system have many
advantages such as simple formwork, reduced floor to II. METHODOLOGY
floor height, reduced construction time and enhanced The ten storeyed RC building is modelled by applying
economical. In this study, the 10 storeyed RC building ETABS software with flat plate system and flat slab
with flat plate and flat slab system have been analysed system. Dynamic analysis (Response Spectrum Analysis) is
by applying ETABS software and slab stresses are used for analysing of the proposed buildings. After
checked by using SAFE software. The proposed analysing, the stability of the buildings is checked out and
buildings are situated in seismic zone 2B. Dynamic the structural behaviour of the buildings is compared.
analysis (Response Spectrum Analysis) has been carried Finally, the slab stresses are checked out by using SAFE
out in this study. Loading requirements are based on software and the results are compared.
UBC-97 (Uniform Building Code) and structural
elements are designed by ACI 318-99. The purpose of III. TYPE OF BUILDING
this study is to analyse and compare the structural The ten storeyed RC building is considered with the flat
behaviour of flat plate building and flat slab building plate system and flat slab system. The two types of
such as story drift, story shear, story displacement, buildings are the following.
natural time period and overturning moment. And then 1. The building with flat plate system
the slab stresses such as slab deflection and punching 2. The building with flat slab system
shear ratio are checked out and compared. According The two buildings are located in seismic zone 2B. The
to comparison of structural behaviour, the flat slab columns, beams and shear wall are same for the two
building is more stable than the flat plate building. And buildings. The flat plate building is provided with edge
then the slab thickness is decreased if the drop panel is beam and the flat slab building is provided with edge beam
used in slab system. In this study, the flat slab system is and drop panel. Ground floor is designed by conventional
more suitable for 30ʹ span RC building. slab system.
A. Design Data
Keywords — Flat plate system, Flat slab system, Story drift,
Story shear, Displacement, Overturning The following tables are described the design data for
moment, Slab stresses the proposed buildings. Table (1) describes material
properties, table (2) describes structural configuration and
I. INTRODUCTION table (3) describes the structural members are used in
In reinforced concrete construction, slabs are used to building.
provide flat and useful surfaces. A reinforced concrete slab TABLE I
is a board, flat plate, usually horizontal, with top and MATERIAL PROPERTIES
bottom surfaces parallel or nearly. There are different kinds
Concrete cylinder strength (fc') 4 ksi
of reinforced concrete floor system such as conventional
slab system, flat plate system, flat slab system, waffle slab Reinforcing yield strength (fy) 50 ksi
system and banded beam system. Among them, the flat
Modulus of Elasticity of concrete 3605 ksi
plate system and flat slab system are widely used in
Myanmar. The flat plate system is a two-way reinforced Poisson’s ratio 0.2
concrete framing system utilizing a slab of uniform
thickness and the simplest of structural shapes. It is
TABLE II
supported directly by concrete column without the use of STRUCTURAL CONFIGURATION
beams, column flares and drop panels. The flat slab is
beamless but incorporates a thickened slab region in the Number of stories 10
vicinity of the column and often employs flared column Width of structure 75'
tops. Both are devices to reduce stresses due to shear and
negative bending around the columns. They are referred to Length of structure 120'
as drop panels and column capitals. In flat plate buildings Total height of structure 109'
and flat slab buildings, the interior beams are not provided
and the shear walls are used for the stiffness of the Typical story height 10'
structure. Shear walls are the structural members which are Ground floor story height 11'
known to resist the lateral loads such as wind and
earthquake etc. The main function of shear wall is to resist Number of bay’s along X-direction 3
the lateral forces. Many research studied which are the
 Fig. 2 3D View of Flat Slab Building
Number of bay’s along Y-direction 4

TABLE III
STRUCTURAL MEMBERS

Flat Plate Building Flat Slab Building

C36"x36" , C28"x28" C36"x36" , C28"x28"

Column
C26"x26" , C22"x22" C26"x26" , C22"x22"
Sizes
C16"x16" C16"x16"
Edge Beam
B16"x30" , B16"x28" B16"x30" , B16"x28"
Sizes
Secondary
B14"x22" B14"x22"
Beam Size
Landing
B14"x20" B14"x20"
Beam
Slab
11" 8"
Thickness
Drop Panel
9'x10'
Size
Fig. 3 Beam and Floor Plan of Flat Plate Building
Shear Wall
12" 12"
Thickness

B. Model Description
The figure (1) and (2) are shown 3D view of the flat
plate building and the flat slab building. The figure (3) and
(4) are shown beam and floor plan of proposed building.

Fig. 4 Beam and Floor Plan of Flat Slab Building

In these proposed building, shear walls are provided at

corner and lift well. The square columns are provided in
these two buildings..

IV. RESULT AND DISCUSSION

Fig. 1 3D View of Flat Plate Building In this section, the results are obtained from the analysis
of flat plate building and flat slab building by applying
ETABS software and SAFE software. And then the results
are tabulated and compared. The stability check of the
structure such as story drift, P-∆ effect, torsional
irregularity, overturning moment and sliding checking are
satisfied. The structural behaviour of proposed building
such as story drift, story shear, story displacement,
overturning moment and time period have been compared
and discussed as follow. Moreover, slab deflection and
punching shear ratio are compared and discussed.
A. Story Drift
Story drift is the lateral displacement of one story
relative to the story above or below. The following figure
(5) and (6) are described the comparison of story drift in X-
direction and Y-direction. From the following figure, it can
be seen that the story drift of flat plate building is more
than that of flat slab building from GF to 5F and the value Fig. 7 Comparison of Story Shear in X-Direction
of story drift is inversed towards top story in X-direction.
2500
In the following figure (6), it can be seen that the story drift Flat Plate
of flat plate building is significantly more than that of flat Building
2000
slab building in Y-direction. The value of story drift is

Story shear (kip)

minimum at ground floor level and is increased towards the 1500
top level in X-direction. In Y-direction, this is minimum at
ground floor level, increased at the middle level and 1000
decreased top level.
500
0

0 0
GF 1F 2F 3F 4F 5F 6F 7F 8F 9F RF
0 Story level
Drift (in)

Flat Plate Fig. 8 Comparison of Story Shear in Y-Direction

0
Building
0 C. Story Displacement
The story displacement is the absolute value of
0
displacement of the story under action of the lateral forces.
0 From the following figure, it can be seen that the
GF 1F 2F 3F 4F 5F 6F 7F 8F 9F RF displacement of the flat plate building is less than that of
Story Level the flat slab building in X-direction and that of flat building
is more than that of flat slab building in Y-direction. The
Fig. 5 Comparison of Story Drift in X-Direction
story displacement is minimum at ground floor level and it
is significantly increased towards the top story of the two
0 buildings.
Flat Plate
Building
0
1.6 Flat Plate
Building
0
Drift (in)

1.2
Displacement (in)

0
0.8
0

0 0.4
GF 1F 2F 3F 4F 5F 6F 7F 8F 9F RF
Story level
0
Fig. 6 Comparison of Story Drift in Y-Direction GF 1F 2F 3F 4F 5F 6F 7F 8F 9F RF
Story level
B. Story Shear Fig. 9 Comparison of Story Displacement in X-direction
The design seismic force to be applied at each floor
level is called story shear. The following figure (7) and (8) 2.5 Flat Plate
show the comparison of story shear in X-direction and Y- Building
direction for the two buildings. From the following figure, 2
it can be seen that the story shear of the two buildings is
Displacement (in)

nearly equal in X-direction and the story shear of flat plate 1.5
building is more than that of flat slab building in Y-
1
direction. The value of story shear is maximum at ground
floor level and is gradually decreased towards the top level. 0.5

2000 0
Flat Plate GF 1F 2F 3F 4F 5F 6F 7F 8F 9F RF
Building Story level
1600
Fig. 10 Comparison of Story Displacement in Y-Direction
Story shear (kip)

1200
D. Overturning Moment
800 Overturning moments are those applied moments, shear
and uplift force that seek to cause the footing to become
400 unstable and turnover. Overturning of the structure is due to
the lateral forces. The following figure (11) and (12) are
0 described the comparison of overturning moment in X-
GF 1F 2F 3F 4F 5F 6F 7F 8F 9F RF direction and Y-direction for the two buildings. The
Story level overturning moment of flat plate building and flat slab
building is nearly coincided in X-direction. In Y- direction,
the overturning moment of flat plate building is more than figure (14) is shown the comparison of slab deflection. The
that of flat slab building. The difference of overturning slab deflections of the two buildings are satisfied because it
moments is dependent upon story shear and additional is less than the slab deflection limitation 0.75 in (L/480).
moment. The deflection of flat slab building is more than that of flat
plate building because of the thickness of flat plate is more
160000 than that of flat slab.
140000 Flat Plate
Building
Overturning moment(k-ft)

0.8
120000
0.7
100000
80000 0.6

Slab deflection (in)

60000 0.5

40000 0.4
20000 0.3
0 0.2 Flat Plate
Building
GF 1F 2F 3F 4F 5F 6F 7F 8F 9F RF 0.1
Story level
0
Fig. 11 Comparison of Overturning Moment in X-Direction 1F 2F 3F 4F 5F 6F 7F 8F 9F RF
Story level
200000
Flat Plate
Building Fig. 14 Comparison of Slab Deflection
Overturning moment (k-ft)

160000
G. Punching Shear Ratio
120000 Punching shear is a type of failure of reinforced
concrete slabs subjected to high localized forces. In flat
80000 plate and flat slab structures, this occurs at column support
points. The failure is due to shear. Punching shear ratio is a
40000 ratio of maximum calculated shear with respect to capacity.
If it has been above 1, it would indicate capacity was
0 exceeded somewhere along the critical section. In the
GF 1F 2F 3F 4F 5F 6F 7F 8F 9F RF
Story level following figure, the punching shear ratio of flat plate
building and flat slab building is less than 1 and it is
Fig. 12 Comparison of Overturning Moment in Y-Direction satisfied. But the punching shear ratio of flat plate building
E. Natural Time Period is more than that of flat slab building because of the drop
panel is provided in flat slab building. Drop panel increases
The following figure (13) is shown the comparison of the shear strength of flat slab and negative moment
natural time period of building with flat plate system and capacity around the column.
flat slab system. The time period is maximum in mode 1, 2
and 3 and after mode 3, the period is significantly 1.2
Flat Plate
decreased. In mode 1, the time period of flat plate building Building
is 1.02 sec and that of flat slab building is 0.96 sec. The 1
time period is equal to the calculated value. The period of
Punching shear ratio <1

flat slab building is a little less than that of the flat plate 0.8
building. This is dependent upon the presence of drop
0.6
panel.
0.4
1.2
Flat Plate 0.2
Building
1
0
Time Period (sec)

0.8 1F 2F 3F 4F 5F 6F 7F 8F 9F RF

0.6 Story level

0.4 Fig. 15 Comparison of Punching Shear Ratio

0.2 V. CONCLUSIONS
1. The value of story drift at GF in flat plate building is
0 more than that of flat slab building in X-direction and
1 2 3 4 5 6 7 8 9 10 11 12 Y-direction. It is dependent upon the structural
Mode shape
elements.
Fig. 13 Comparison of Natural Time Period 2. The value of story shear in flat plate building is
F. Slab Deflection coincided that of flat slab building in X-direction and
the story drift of flat plate building is more than that of
Deflection in concrete is the movement of a point on a flat slab building in Y-direction. It is dependent upon
structure or structural element, usually measured as a linear the building weight and structural elements.
displacement to a reference line or axis. The following
3. The displacement of flat plate building is a little less
than that of flat slab building in X-direction and that of
flat plate building is more than that of flat slab building
in Y-direction.
4. Overturning moment is nearly equal in the two building
in X-direction and the overturning moment of flat plate
building is more than that of flat slab building in Y-
direction. This is dependent upon the building weight.
5. The deflection of flat slab is more than that of flat plate.
This is that the thickness of flat plate is thicker 3 in than
thickness of flat slab.
6. In comparison of punching shear ratio, the flat plate is
more than the flat slab.
Considering all the above results and comparisons, the
flat slab building is more stable than the flat plate building.
According to comparison of slab stresses, flat plate is more
resist deflection so the thickness of slab is thicker. The flat
slab is more resist punching shear due to the provision of
drop panel. Thus, the slab thickness is decreased if the drop
panels are used. In this 30' span building, the flat slab
system is more suitable than the flat plate system.

ACKNOWLEDGMENT
The author wishes to express grateful thanks to Dr.
Theingi, Rector of Technological University (Thanlyin).
The author wishes to express the deepest thanks to Editorial
Teams of URJEAS in Technological University (Hpa-an).
The author special thanks go to his co-author Daw Phyoe
Hnin Thu Htun, Lecturer of Civil Engineering Department
of Technological University (Hpa-an), for her invaluable
advice and effective suggestion throughout the study. The
author would like to express his thanks to his partners in
Civil Engineering Department of Technological University
(Thanlyin), for their valuable comments during this study.
Finally, his special thanks to all who helped his towards the
successful completion of this study.

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