International Journal of Innovative Technology and Exploring Engineering (IJITEE)

ISSN: 2278-3075, Volume-9 Issue-3, January 2020

Seismic Analysis of Flat Slab by using ETABS

S. Dhana Sree, E. Arunakanthi

Abstract: The flat slab is a two-way reinforced concrete slab Flat slabs are the cost effective and built in shorter
that usually does not have beams and girders, and the loads are durations. This paper is the analysis of seismic forces in flat
transferred directly to the supporting concrete columns. ETABS slabs. These flat slabs reduce the usage of number of beams
automates several slab and mat design tasks. Specially, it by directly resting the slab on columns and column heads.
integrates slab design moments across design strips and designs
This provides decrease in cost of construction along with
the required reinforcement; it checks slab punching shear
around column supports and concentrated loads; and it designs aesthetic view and fast rate in construction time. There are
shear link and shear stud if needed. The actual design algorithms many techniques for the analysis of structures under
vary based on the specific design code chosen by the user. This different type of loading conditions. Among them Non-
manual describes the algorithms used for the various codes. Linear Time history is accurate. For less important or
Recent earthquakes in which many concrete structures have seismic hazard, other methods like Non-Linear Static
been severely damaged or collapsed, have indicated the need for methods are used.
evaluating the seismic adequacy of existing buildings. About 60% These flat slabs are mostly used in commercial complexes
of the land area of our country is susceptible to damaging levels like cinema halls, shopping malls, high rise buildings and
of seismic hazard. Many existing flat slab buildings may not have
many more structures.
been designed for seismic forces. Hence it is important to study
their response under seismic conditions and to evaluate seismic
retrofit schemes. This system is very simple to construct, and is II. FLAT SLABS
efficient in that it requires the minimum building height for a
Slabs are generally two types based on length to depth ratio
given number of stories. Unfortunately, earthquake experience
has proved that this form of construction is vulnerable to failure, as one way and two way slabs which rests on horizontal
when not designed and detailed properly, in which the thin members like beams. When the ratio of length to depth is
concrete slab fractures around the supporting columns and drops less than two then it is called two way slab and when the
downward, leading potentially to a complete progressive collapse ratio is greater than two is called one way slab. Various
of a building as one floor cascades down onto the floors below. types of loads acting upon the slabs are transferred from
Although flat slabs have been in construction for more than a
beams to columns, walls, lintels then to foundations and
century now, analysis and design of flat slabs are still the active
areas of research and there is still no general agreement on the finally distributed over soil. Number of stories could be
best design procedure. To study the effect of drop panels on the increased through proper design by reducing floor height
behavior of flat slab during lateral loads, flat plate system is also while going to upper stories to maintain stability to the
analyzed. Zone factor and soil conditions- the other two structure.
important parameters which influence the behavior of the Flat slabs are widely implemented when there are many
structure, are also covered. Software ETABS is used for this
stories for commercial buildings in order to reduce cost of
purpose. In this study relation between the number of stories,
zone and soil condition is developed. construction along with good aesthetic view in shorter
Keywords: Concrete column, Drop panels, ETABS, Flat slab, duration. Due to elimination of unnecessary beams ceiling
Minimum building height, Seismic force. can be used to maximum extent which leaves a pleasant
experience. Partitions could be made easily along with
I. INTRODUCTION mechanical and electrical maintenance.
In the present world, with the increase in population
growth, need for shelter and growth of country’s economy III. LITERATURE REVIEW
demanding for infrastructure growth in the limited land area Many researchers carried out their work in finding
suitable for construction. With the view of limited suitable responses of structures towards earthquake and many
land, cost of land and building materials cost, construction loading conditions like static and dynamic loads along with
plays a prominent role in effective execution of a building. the view of soil pressures.
Earthquake phenomenon plays important role due to Lan N Robertson (1997) performed analysis of flat slab
movement of tectonic plates in Earth’s lithosphere. building by considering a three dimensional model when
Earthquake does not kill cause much damage to life but loads acting on horizontal and vertical frame elements.
cause severe damages to concrete structures like buildings, These are correlated to experimental studies. This analysis
roads, bridges and many more. Therefore, design of a give values about horizontal drift. These models are
concrete structure should be done properly keeping in view incapable to re-obtain the flexural moments at 0.5 or 1.5 %
of various parameters. There are various techniques which drift levels. Replacement of one beam with two at contra
are used in present world to overcome the boundaries in flexure, the difference in the positive and negative moments
construction sector. A structure could be analyzed both by were calculated.
manually and through software accordingly to maintain R. P. Apostolska, G. S. Neenska-Cvetanovska, (2008) in
quality and perfection in design. their paper summary flat slabs with proper design and
modifications with consideration of other parameters
Revised Manuscript Received on January 05, 2020. improve resistance, durability and seismic behavior of flat
S. Dhana Sree, PG Student, JNTUA College of Engineering,
Ananthapuramu (Andhra Pradesh) India.
slabs in construction.
Dr. E. Arunakanthi, Professor at JNTUA College of Engineering,
Ananthapuramu (Andhra Pradesh) India.

Published By:
Retrieval Number: B6215129219/2020©BEIESP
Blue Eyes Intelligence Engineering
DOI: 10.35940/ijitee.B6215.019320 1142 & Sciences Publication
 Seismic Analysis of Flat Slab by using ETABS

K. S. Sable et al (2012), comparison between flat slab and c.Compressive strength of concrete, fck=25MPa
conventional structure made. The modeling and analyzing d.Yield stress for steel, fy=415MPa
done by using STAAD Pro 2007. Analysis made for 11
storied structure. Though storey increase provision of shear
wall make it same.
Salman I Khan and R. Mundhada (2015), analyzed with 12, D. Design Variables for Analysis
15, 18 storey by taking into account seismic zones using
ETABS. It is found that at terrace level base shear of flat
slab is more than grid slab. The storey drift and time period Design variable Value Remarks
will be more for flat slab than the grid slab.

IV. PROCEDURE Static loads

Consideration of earthquake effect makes the structure IS
withstand the trembling effect to maximum extent. Design 875:1987(Part-1)
(a) Masonry 20kN/m3
should consider severity of horizontal movement of building
obtained by following mode shapes. First mode is called
fundamental mode which indicates the movement of a
(b) Concrete 25kN/m3
structure predominantly.

Dynamic loads

(a) Floor load 2kN/m2

IS
(b) Roof load 1.5kN/m2 875:1987(Part-1)

(c) Floor finishes 1.0kN/m2

Fig. 1. First and second modes of building seismic
response
A. Linear Static Analysis Importance factor 1.0 IS 1893:2002
Single degrees of freedom (SDOF) is the linear static
analysis with viscous damping coefficient. There are various
methods to determine the stresses and strains objective to
Seismic zone factor 0.36 IS 1893:2002
produce the same stresses and strains using Rayleigh
method, spectrum method, time history. Parameters like
second degree effects, stiffness and reduction in force . Response reduction
Force is distributed to different stories in order to reduce factor 5 IS 1893:2002
more impact. Linear static analysis is considered in many
codes. Their usage is less due to its predominance of first
mode in normal structures.

B. Earthquake Resistant Design of Buildings

Earthquake resistant structures are capable of sustaining the
severe effect of horizontal movement of the earth. Indian
code IS 456-2002 is used to design structures resistant
towards earthquake. Intensity of earthquake determined by
using an instrument called Richter scale. Proper care must
be taken while designing a structure. Earthquake zones are
divided as Zones from I-V whereas, Zone I the safest place
to resist the damage due to earthquake. Zone II is next safe
place. Zone III, Zone IV and Zone V are much prone to
earthquake damages. Based on the zone of structure to be
constructed various parameters must be considered like
response reduction factor, intensity factor, importance factor
and so on to make the structure earthquake resistant.
Fig. 2. Plan of G+17 Structure
C. Modeling in ETABS
ETABS is used to view the response of a structure towards
earthquake vibrations.
M-25 concrete grade is utilized and Fe-415 reinforcing
steel is used as per IS 456-2000.
a.Elasticity of Steel, ES=21,000MPa
b.Elasticity of Concrete, EC=22360.68MPa

Published By:
Retrieval Number: B6215129219/2020©BEIESP
Blue Eyes Intelligence Engineering
DOI: 10.35940/ijitee.B6215.019320 1143 & Sciences Publication
 International Journal of Innovative Technology and Exploring Engineering (IJITEE)
ISSN: 2278-3075, Volume-9 Issue-3, January 2020

V. RESULTS AND DISCUSSIONS 4. Above results shows that flat slab with proper design
against earthquake could resist the damage to considerable
Structure Data
extent.
Height Elevation Master Similar Splice
Name To increase the resistance towards lateral and longitudinal
Mm mm Story To Story
effects on a concrete structure factor of safety parameters
Story18 3000 54000 Yes None No and also other loading parameters need to be considered
Story17 3000 51000 No Story18 No while designing the structure.
Story16 3000 48000 No Story18 No
REFERENCES
Story15 3000 45000 No Story18 No
1. Ahmad J. Durrani, S. T. Mau and Yi-Li (1994). “Earthquake
Story14 3000 42000 No Story18 No Response of Flat Slab Buildings, Journal of Structural
Engineering”, Vol. 120.
Story13 3000 39000 No Story18 No 2. Apostolska R. P., G. S. Necevska-Cvetanovska, J. P.
Story12 3000 36000 No Story18 No Cvetanovska and N. Mircic (2008), Seismic performance of flat
slab building structural systems. The 14th World Conference on
Story11 3000 33000 No Story18 No Earthquake Engineering October 12-17, 2008, Beijing, China.
3. Salman I. Khan and Ashok R. Mundhada (2015), Comparative
Story10 3000 30000 No Story18 No study of seismic performance of multistoried RCC Building
with Flat Slab and Grid Slab: A Review, IJSCER, ISSN 2319-
Story9 3000 27000 No Story18 No 6009, Vol. 02-Feb 2015.
Story8 3000 24000 No Story18 No 4. Sable K. S., Ghodechor V. A., Khandekar S. B. (2012),
Comparative Study of Seismic Behaviour of multistoried flat
Story7 3000 21000 No Story18 No slab and conventional reinforced concrete framed structures,
International Journal of Computer Technology and Electronics
Story6 3000 18000 No Story18 No Engineering, Volume 2, Issue 3, June 2012.
Story5 3000 15000 No Story18 No 5. Navyashree K, Sahana T. S (2014), Use of flat slabs in
multistoried commercial building situated in high seismic zone,
Story4 3000 12000 No Story18 No IJRET: International Journal of Research in Engineering and
Technology, Volume: 03 Issue: 08| Aug-2014.
Story3 3000 9000 No Story18 No
Story2 3000 6000 No Story18 No AUTHORS PROFILE
Story1 3000 3000 No Story18 No
Base 0 0 No None No S. Dhana Sree, PG Student at JNTUA
College of Engineering, Ananthapuramu,
Andhra Pradesh, India.

Dr. E. Arunakanthi, Professor at JNTUA

College of Engineering, Ananthapuramu,
Andhra Pradesh, India.

Fig. 3. Axial force and bending moment of conventional

slab (Ground Floor)

VI. CONCLUSIONS
Flat slab structures give aesthetic appearance along with
economical gain and resisting capacity towards earth
movement. Due to no beams with more depth, flat slab
structures are able to take lateral loads and results in more
vulnerable under seismic events.
1. The bending moments and axial forces are maximum for
flat slab building.
2. The maximum displacements of both the structures are
within the permissible limit. Storey displacement is more
at top storey and less at base of the structure. With
increase in building height displacement also increases.
3. Storey drifts are maximum in the middle stories. That
means columns are stiffer in bottom and top stories and
weaker in the mid level of the structure.

Published By:
Retrieval Number: B6215129219/2020©BEIESP
Blue Eyes Intelligence Engineering
DOI: 10.35940/ijitee.B6215.019320 1144 & Sciences Publication