Comparative Study of Waffle Slab and Conventional Slabs with Bracing System Using Time History Analysis

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 09 Issue: 08 | Aug 2022 www.irjet.net p-ISSN: 2395-0072
© 2022, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page 779
Comparative Study of Waffle Slab and Conventional Slabs with Bracing
System Using Time History Analysis
Shivani Singh1, Vinayak Mishra2
1(M.Tech. Structural Eng.), Civil Engineering Department, Institute of Engineering and Technology, Lucknow
2Assistant Professor, Civil Engineering Department, Institute of Engineering and Technology, Lucknow
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Abstract - An Earthquake ground motions are greatly
influenced by the analysis and design of structure. Analysis of
the structure with various slab arrangements, such as
standard slabs, grid/waffle slabs, and braced structures, isthe
goal of this work. Traditional slab designs are typically not
chosen for large span structures, but waffle slab and ribbed
slab are the most appropriate and cost-effective options.
However, these slabs have recently seen significant growth as
these are lighter, durable and shows minimal signs of visible
damage due to presence of waffle pod in the slabs. The
bracing system allows load to be transmitted from the frame
to the braces, increasing the structure's capacity to withstand
lateral loads. Using ETABS software, time history analysis is
performed in order to study the seismic stresses' effects on
structures with different slab layouts. Storey drift, base shear,
and storey displacement are among the parameters thathave
an impact on a structure's performance and are vital in
determining how building will respond under seismic loads
and other load combinations. IS 456-2000 code is taken into
consideration for designing purpose. Live loads are taken in
accordance to IS 875-part 1 and earthquake analysis is
performed according to IS 1893-2016 Part 1
Key Words: Waffle Slab, Conventional Slab, Bracing
System, Time history analysis, Multi-storey building
1. INTRODUCTION
This An earthquake is strong shaking of the earth resulting
from the energy released by tectonic plate movement. Often,
earthquakes result in severe damage to life and property[1].
An expanding quantity of research has been conducted in
this area due to the growing interest in designing
earthquake-resistant constructions or buildings [2]. It is
critical to ensure that the structure is capable of
withstanding horizontal ground vibrations. RCC slab
structure is an important part of the building that is
designed to bear both vertical and horizontal loads during
earthquakes. While, conventional slab is one that is
supported by standard beams and columns. In a typical slab,
the load is distributed from the slab to the beam,thebeamto
the column, and the column to the foundation. [3]. On the
other hand, waffles are made to cover large span with least
possible & have been widely used nowadays in both
residential and commercial structures such as auditoriums,
airports, theatre halls, and show rooms, roofing etc. where
there is minimal or no need for columns. The severity of the
quakes and the qualities of the structure determine a
structure's strength and stability during an earthquake.
Bracing is an economical and efficient way to strengthen the
frame structures against lateral loads. The steel braces are
usually placed in vertically aligned spaces.[4] Steel bracing
are cost-effective, easy to install, takes up less area and
provide the extra strength and stiffness. Braced frames are
highly effective for structures subjected to severe lateral
loads, such as earthquake loads. Time history analysis is an
adaptive method for evaluating seismic behaviour of multi-
storey building for the range of seismic intensities in order
to understand how parameters such as storey shear ,
displacement, storey stiffness etc. affects seismic
performance[5].The primary goal of the study is to evaluate
the structural behaviour using waffle slab and conventional
slab with X- type bracing in seismic zone IV in type
II(medium) soil .
2. Literature Review:
Kaushal Vijay Rathod, Sumit Gupta[2020]: This research
paper discusses the outcomes of a time history study
performed on a ten-story building. There is a necessity to
study seismic analysis in order to develop earthquake
resistance structures in order to assure safety against
seismic forces of multi-story buildings. This seminar report
uses ETABS to do a nonlinear time history analysis on a ten-
story RCC building frame while taking into account the
timing of the 1940 El Centro Earthquake[6].
The work by Dhanaraj M. Patil , Keshav K. Sangle [2015]:
The seismic response characteristics of various structures
with distinct bracing methods are evaluated in order to
evaluate seismic behaviour of each system.
Manoj Kumar M, Victor Samson Raj A,et al [2020]: A
structure's ductility and energy dissipation capability play a
key role in its ability to withstand seismic force. Bracingwas
utilized to increase a steel-framed structure's ability to
dissipate energy. Here, a steel-framed G+14 story building
was chosen for examination. The addition of the X, V, and
zipper bracing increased the ability of these structures to
dissipate energy. For the analytical analysis,STAADPROand
SAP2000 are used. Pushover analysis is used to relate the
performance of the various braced framedstructures.Forall
steel frames, the positioning of the bracings on the edge

structure has raised the base shear conveying limit, raised
the performance point, and decreased the displacement of
the roof.
As per previous study by Mirza Mahaboob Baig, , Abdul
Rashid , Y Pavan Sai Durga Reddy et.al 2020: Thepurpose
of their study is to determine behaviour of waffle slab
constructions when the obstructing columns have been
removed from the building’s hall and room. This study
concludes that ribbed/waffle slab structures are more
susceptible to lateral loads thanconventional slabstructures
because of an increase in self-weight. The research was
carried out in seismic zone III and it was found that, in high
seismic zones, ribbed slab structures perform less than
conventional slab buildings because they have fewer
columns, but that performance can be improved by
structural retrofitting[4] .
Sawwalakhe, A. K., & Pachpor, P. D. (2021): The study's
goal is to determine which of the regular slab, flat slab with
drop, and grid floor is the most economical. For a G+5
commercial multi-story structure with a flat slab, a
conventional slab, and a gird slab, variables such as storey
displacement, shear force, bending moment, and storeys
drift were examined in this work. The total number of
structures studied for this purpose is 18. All structures in
India's seismic zone III have had their performance and
behaviour examined using dead load, live load, and seismic
load.[7].
2.1. Research Significance:
1. To compare the performance-based analysis of
conventional slab and waffle slab in commercial
building of seismic zone IV.
2. To perform time history analysis on conventional
slab and waffle slab.
3. To study and compare the seismic parameters such
as storey drift, storey shear, displacement, and
storey stiffness, joint displacement etc.
3. Methodology:
This paper includes modelling G+4 building by creating a
plan of dimension 45m*45m with storey height of 5m each.
Defining & assigning properties of materials, RC frame
section properties and load condition, using ETABSv16
software. Then we define time history function taking
Chamoli earthquake data as reference for the analysis& the
study is performed on seismic zone IV.
3.1 Modelling Parameters:
Table 1: Building parameter
Area of the building 45*45 m2
Height of the building 25m
Columns C1 450*450mm2
C2 450*350 mm2
C3 450*600 mm2
Beams B1 350*400 mm2
B2 350*500 mm2
Slab Type Waffle slab
Slab thickness 90mm
Spacing of ribs 1500mm
Width of ribs 200mm
Overall depth 800mm
Bracings X-type (ISA 200*200*15)
Table 2: - Material properties:
3.2 Loading Conditions:
Fig1. Loading Properties

3.2 Structural Modelling:
Fig 2: Elevation View Of Both Models
Fig 3: Plan View of The Slab
Fig 4: Conventional Slab
Fig 5: Waffle Slab
Fig 6: Waffle Slab with X-bracing
Fig 7: Conventional Slab with X-bracing

4. Results and Discussion:
As a result of comparison between the braced and non-
braced G+4 structure , following inferences has been made:
4.1 Joint Displacement:
The maximum joint displacement at 23.24sec. is found to
be 492.455mm in conventional slab. Similarly, the max value
of joint displacement for waffle slab is found to be
263.666mm at 5.02sec. The value for waffle slab is observed
to be 47% less than that of conventional slab.
Chart 1: Displacement due to Conventional Slab
Chart 2: Displacement due to Waffle Slab
4.2 Storey Drift:
As per IS 1893 (part 1): 2002 CI. 7.11. 3, the storey drift
limit is 0.004 times the storeyheight[8]. andaccording tothe
graphs obtained maximum drift is 0.001655 on waffle slab
and .0010588 on conventional slab which is within the
permissible limits.
Chart 3: Storey Drift
4.3: Storey Stiffness:
Storey stiffness is a more for conventional slab structure
in comparison to waffle slab structure. The value gradually
increases movingfrombottomtotopstoreyreachespeakand
fall suddenly.Themaximumvaluesobtainedforconventional
slab and waffle slab are 668862.633 kN/m & 657529.69
kN/m.
Chart 4: Storey Stiffness
4.4 Storey Displacement: Storey displacement is
maximumatthetopstorey(27.361mm)forconventionalslab
and minimum at the structure’s base. While for waffle slab
the maximum displacement is (24.26mm). Max value of
storey displacement for waffle slab is approx. 16% less than
the maximum value of displacement in the other.

Chart 5: Displacement of buildings
5. Conclusions:
Comparative study of waffle slab and conventional slab
both havingbracingsystemusingtimehistoryanalysisshows
that waffle slab has approx 12% less displacement than
conventional slab i.e, waffle slab performs better when it
comes to lateral joint displacement of joint label 1, Storey 5.
While the maximum values of storey drift conclude that
waffle slab shows lower drift i.e. approx. 57% lower than
conventional slab storeydriftvalues.Anystorey'sstoreydrift
induced by the required minimum designed lateral force,
with a partial load factor of 1.0, may not be larger than 0.004
times the storey height, per IS 1893 Part 1: 2002 Cl. 7.11.3.
The plots show a maximum drift of 0.02, which is within
acceptable bounds. Moreover, conventional slab shows
slightly lesser Storey stiffness ascompared to waffle slab [9].
However, storey displacement values conclude that
conventional slab displaces 11% more than waffle slab.
Hence, this can be concluded from the results that
conventional slab lags behind in someaspects such as storey
displacement and drift in comparison towaffleslabi.e,waffle
slab performs better withbracingswhichreducesdeflections
and increases stability of the structure.
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6. References:
[1] C. H. Lokesh Nishanth, Y. Sai Swaroop, D. C. K.
Jagarapu, and P. K. Jogi, “Analysis and design of commercial
building with different slab arrangements using ETABS,” in
Materials Today: Proceedings,Jan.2020,vol.33,pp.700–704.
doi: 10.1016/j.matpr.2020.05.823.
[2] V. P. Thakkar, A. K. Chandiwala, and U. D. Bhagat,
“Comparative Study of Seismic Behavior of Flat Slab and
Conventional RC Framed Structure.” [Online]. Available:
www.ijert.org
[3] “COMPARATIVE STUDY OF THE SEISMIC
PERFORMANCE OFRCCBUILDINGWITHRIBBEDSLABAND
GRID SLAB 140.”
[4] M. M. Baig, A. Rashid, Y. P. S. D. Reddy, and T. G. N. .
V. Krishna, “A comparative study on seismic analysis of G+6
building with ribbed slab&conventional slabusingSAP2000
software,” IOP Conf. Ser. Mater. Sci. Eng., vol. 1112, no. 1, p.
012026, Apr. 2021, doi: 10.1088/1757-
899x/1112/1/012026.
[5] D. M. Patil and K. K. Sangle, “Seismic Behaviour of
Different Bracing Systems in High Rise 2-D Steel Buildings,”
Structures, vol. 3, pp. 282–305, Aug. 2015, doi:
10.1016/j.istruc.2015.06.004.
[6] K. V. Rathod and S. Gupta, “A nonlinear time history
analysis of ten storey rcc building,” Int. Res. J. Eng. Technol.,
vol. 7, no. June, pp. 56–2395, 2020.
[7] A. K. Sawwalakhe and P. D. Pachpor, “Comparative
Study Of Conventional Slab, Flat Slab And Grid Slab Using
ETABS,” IOP Conf. Ser. Mater. Sci. Eng., vol. 1197, no. 1, p.
012020, Nov. 2021, doi: 10.1088/1757-
899x/1197/1/012020.
[8] I. Standard, “la jpukvksa osQ HkwdEijks / h fMtkbu
osQ ekunaM Criteria for Earthquake Resistant Design of
Structures,” vol. 1893, no. December, 2016.
[9] IS 456, “Plain Concrete and Reinforced,” Bur. Indian
Stand. Dehli, pp. 1–114, 2000.
[10] Rathod, K. V., & Gupta, S. (2020). A nonlinear time
history analysis of ten storey RCC building. International
Research Journal of Engineering and Technology, 8.

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