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7/23/2019 Comparison of Reinforced Concrete and Pre-stressed Concrete Flat Slabs in Tall Buildings
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I JSRD - I nternational Journal for Scientifi c Research & Development| Vol. 3, I ssue 08, 2015 | ISSN (onli ne): 2321-0613
All rights reserved by www.ijsrd.com 607
Comparison of Reinforced Concrete and Pre-Stressed Concrete Flat
Slabs in Tall Buildings Ruchi R Kadamb1 M.Manjunath2
1P.G. Student 2Associate Professor 1,2Department of Civil Engineering
1,2KLE Dr. M.S.Sheshgiri College of Engineering and Technology, Belgaum 590008, India Abstract
— Flat slab are usually preferred floor system for
tall buildings as they result in reduction in floor heights. The
flat slabs without drop panel and column head are called as
flat plates. The design of tall buildings is usually governed
by the lateral loads imposed on the structure. The main
disadvantage of flat slabs and flat plates is their lack of
resistance to lateral loads, such as those due to wind forces
and earthquakes. In the present study tall building with
reinforced concrete flat slab floor system is compared with
pre-stressed concrete flat slab floor system under lateral
forces. A 30 storied tall building with a flat plate floor of
size of 30m x 24m and having a panel size 6m x 6m is
studied for wind forces. These slabs are design as reinforced
concrete as well as pre-stressed (post tensioning) concrete
flat slabs as per Indian standard codes and analysed in
software SAP2000. The analysis and design results of
reinforced concrete and pre-stressed concrete flat plates are
compared to evaluate the performance of the tall building inresisting the lateral wind forces.
Key words: Reinforced Concrete, Pre-Stressed Concrete Flat
Slabs
I. I NTRODUCTION
Tall buildings are developing in a rapid speed nowadays.
Since last 20 years they have gained a lot of importance in
commercial as well as residential buildings. For the businessactivist it is a mark of prestige to own a high rise building at
city centres. A building is said to be tall building when it has
stories more than 10.
The reason behind the rapid construction of tall
buildings is mainly due to economic growth, human
curiosity in building tall structures, increase in population at
a fast rate, land scarcity in urban areas. Land rates have boomed in last few years to a very high cost. Hence tall
buildings make it economical for the people. There is a lot
of improvement in technology and advancement in studies;
this is another reason for the increase in tall building.
As of today there are lot of software which makes
it easier for a structural engineer to analyse a building andget the values to design building in a short period of time.
The conventional manual analysis consumes a lot
of time to design a tall building, hence it is a difficult task to
analyse the building with conventional methods. Hong Kong
is the world’s largest high rise building centre. They have a
lot of tall buildings with the most promising designs for a
structural engineer.
Tall buildings have to resists large amount of loads
such as gravity loads, wind loads and earthquake loads.
Earthquake loads and wind loads are most dominant in such
multi storied buildings. Therefore structures are built toresist these loads by providing several load resisting
systems. Few methods are by providing bracing to the buildings, by constructing a shear wall or coupled shear
wall. For earthquake loads damper are used to resists thevibrations in the building during an earthquake attack.
II. LITERATURE REVIEW
In one of the previous work, the effects of wind loads on
tall buildings are studied. For this investigation 3D models
are prepared in ETABS software. By changing the aspect
ratio up to 2 of the buildings these studies are carried out.
Design is as per IS-875 part III. Even the height of buildings
are varied, buildings from 3 to 20 stories are used. For this
study parameters such as bending moments and axial forces
are included. A building of width 20 meters with 4 bays is
considered for the design purposes. Graphs are drawn by togive out the conclusion to these investigations. Graphs of
moment v/s aspect ratio, moment v/s height, and axial loadv/s aspect ratio are drawn. From these graphs it is proved
that as the aspect ratio reduces wind loads also reduces.
It is concluded that aspect ratio increases as
moments in the column decreases for wind load cases, but
the moments remain same for all aspect ratio for gravity
loads. As the height increases moments in the column
increases for low rise building and remain constant for
medium height buildings. Axial forces in the column are
almost same for all load cases when the height of building is
less than 15mts. Column moments are considered critical
while designing for the tall buildings.
III. PROBLEM DEFINITION AND METHODOLOGY
Basically in this investigation a flat slab performance on a
tall building is studied. Drop panel and column capital isabsent in these slabs. Building of 30 stories is used in this
project and parametric study is carried out to study the
details of wind loads acting on the buildings along with
gravity loads. For the analysis first design is manually done
using Indian standard codes. IS 875 part III, IS 456 2000, IS
875 part I and II and IS 1343.
These design values calculated are applied on the
high rise building to create 3D models in SAP 2000 and get
the analysis results. The results obtained from this softwareare displacements, axial loads, moment, shear values joint
reactions, joint displacements, element forces and momentsfor both shell and frame. These values are used in this
project to compare the flat slab performance. For both the
cases design is manually done and model is created in the
software.
The analysis model for reinforced concrete tall
building and pre-stressed concrete tall building are asfollows:
7/23/2019 Comparison of Reinforced Concrete and Pre-stressed Concrete Flat Slabs in Tall Buildings
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Comparison of Reinforced Concrete and Pre-Stressed Concrete Flat Slabs in Tall Buildings
(IJSRD/Vol. 3/Issue 08/2015/156)
All rights reserved by www.ijsrd.com 608
Fig. 1: SAP 2000 3D model of Reinforced concrete
Fig. 2: SAP 2000 3D model of pre-stressed concrete
IV. R ESULTS AND DISCUSSION
A. Axial Loads Variations for Reinforced Concrete and
Pre-Stressed Concrete Flat Slab Buildings of Columns on
Lee Ward Side and Wind-Ward for the Combination1.2(DL+LL+WL)
Fig. 3: Variation of axial loads on lee-ward side of building
for combination 1.2(DL+LL+WL)
Fig. 4: Variation of axial loads on wind-ward side of
building for combination 1.2(DL+LL+WL)
B. Axial Loads Of Building For Reinforced Concrete And
Pre-Stressed Concrete Flat Slab Buildings Of Columns With
No Wind Load Acting On The Building That Is For TheCombination 1.5(DL+LL)
Fig. 5: Variation of axial load on external columns with no
wind loads acting on the building
C. Displacement variation of reinforced concrete and pre-
stressed concrete flat slab buildings for load combination
1.2(DL+LL+WL).
Fig. 6: Change in displacement of building with respect to
story height
D.
Column Moments of Reinforced Concrete and Pre-Stressed Concrete Flat Slab Buildings for Load
Combination 1.2(DL+LL+WL)
Fig. 7: Bending moment variation on wind-ward side of
building for load combination 1.2(DL+LL+WL)
Fig. 8: Bending moment variation on lee-ward side of
building for load combination 1.2(DL+LL+WL)
7/23/2019 Comparison of Reinforced Concrete and Pre-stressed Concrete Flat Slabs in Tall Buildings
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Comparison of Reinforced Concrete and Pre-Stressed Concrete Flat Slabs in Tall Buildings
(IJSRD/Vol. 3/Issue 08/2015/156)
All rights reserved by www.ijsrd.com 609
V. CONCLUSION
From the analysis made on reinforced concrete and pre-
stressed concrete flat slab buildings following conclusion
can be arrived. The axial loads and moment in columns of
pre-stressed concrete flat-slab building are 25% lesser thanreinforced concrete flat-slab building for both lee-ward side
columns as well as wind-ward side columns. The
displacement of pre-stressed concrete flat-slab building islower as compared to reinforced concrete flat-slab building.
The reduction in displacement is about 30%. This indicates
that the pre-stressed concrete flat-slab system enhances the
stiffness of the tall structure. All the above points prove that
pre-stressed concrete flat-slab systems are more suitable
than reinforced concrete flat-slab systems for tall buildings.
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