Highlighting the alternative measures for advancement in the design of the irregular multi-storey buildings for natural disasters like Earthquakes.

1. Disaster Advances Vol. 8 (10) October (2015)
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Seismic Design for Floating Column
multi- storeyed Building
Chakravarthy P.G. Malavika*
, Poleswarao K., Balaji K.V.G.D. and Shashidhar K.
Department of Civil Engineering, GITAM University, Vishakhapatnam, INDIA
*pgmc92.ce@gmail.com
Abstract
Modern multi-storey buildings are constructed with
irregularities such as soft storey, vertical or plan
irregularity, floating column and heavy loads. It is
observed that most of the RC structures with such
irregularities constructed in India are highly
undesirable in seismically active areas from the
results of past earthquake studies. This study explains
the seismic analysis of a multi-storey building with
floating column constructed in seismically active
areas observing its reactions to the external lateral
forces exerted on the building in various seismic
zones using the software ETABS.
Thus highlighting the alternative measures for
advancement in the design of the irregular buildings
for natural disasters like earthquakes involves in
improvising the non-uniform distribution in the
buildings such as multi-storey building with floating
column. The safer design of such building is
recommended in seismically active areas considering
the results observed from storey drifts, storey
displacements when compared to Response Spectrum
method.
Keywords: Soft storey, Floating column, Vertical and Plan
irregularity, Storey drifts, Displacement.
Introduction
India is a developing country where urbanisation is at the
faster rate and also a vast development in adoption of the
constructions techniques for past few decades i.e. including
in adopting the methods and type of constructing buildings
for the advances in the design of the building to resist
disaster like earthquake effects and as a part of urbanisation
multi-storey buildings with architectural complexities such
as soft storey, floating column, heavy load, the reduction
in stiffness etc. are constructed. Nowadays most of the
urban multi-storey buildings have opened first storey as
an unavoidable feature for accommodation of parking or
reception lobbies. But Conventional Civil Engineering
structures are designed on the basis of strength and stiffness
criteria.
Floating Column: “A vertical member that transfers load to
the ground from foundation is called as a column and the
term “floating column” also refers to a vertical member
resting on a beam i.e. a horizontal member.” There are
numerous projects in India where the floating column is
already adopted and usually the transfer girders are
employed at the position. Generally these floating columns
are adopted at the ground floor such that more open space
can be available on the ground floor. This study highlights
the behaviour of a multi-storeyed buildings with floating
column at higher seismic zones using ETABS.
In this present study, the following aspects are attempted for
study:
1) Modelling of the multi-storey building with and without
floating column using the software ETABS,
2) Comparative study on variations in the structural
response between the multi-storey building with and
without floating column in Zone 5.
3) The building with floating column tend to fail at seismic
excitations and hence the recommendations for the
earthquake resistant design of the considered
buildings are modelled and analysed.
4) The main objective of the study is to provide an
economical and safe design with some design
recommendations as there is no specified provision
provided in I.S codes for this type of irregularities to
afford natural or manmade disasters.
Modeling
For analysis and study purpose there are few models
developed in this study such that a multi-storey building
that is stilt+G+4 building is considered and modelled into
two types mainly. They are multi-storey building without
floating column that is a “Normal building” and the other
type is multi-storey building with “Floating column in the
same floor at different positions in it”. These two types of
structures are modelled and analysed using the software
ETABS.
ETABS is a fully integrated structural program based on
stand alone finite element method for the design and
analysis of civil structures that allows results review within
a single interface for model creation, modification, design
optimization and execution of analysis.
This study discussed the results obtained at Zone 5 when
two frames are analysed. Hence the results are tabulated by
focusing the parameters like storey displacements and
storey drift.
The models details are:

2. Disaster Advances Vol. 8 (10) October (2015)
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Model 1: Stilt+G+4 building models with and without
floating column at Edge column position, Centre portion
and Parallel positions in Zone 5.
Model 2: Stilt+G+4 building models with floating column
with Recommendations such as Shear walls, Infill walls and
Steel bracings in Zone 5.
Results and Discussion
A comparative study and analysis is performed between a
normal building that is the building with all regular
columns and other structural and non-structural members in
it and on the other hand a floating column building at
various zones as per the specifications in IS-1893(2002)
part 1. A detail study is carried out to find the structural
response of the building with floating column at “one Edge
column position, at the centre column positions and parallel
column position” where the maximum displacements in the
building at each floor and the storey drifts are the results
obtained as follows. As per IS 456-2000 and IS 1893(part
1)-2002, it is observed that the Maximum displacements and
Storey Drifts are beyond deformation allowable limits.
Then such a floating column building tends to fail in
disaster situations like large earthquake excitations, thus
some recommendations are performed to analyse the
building response in that case. The recommendations are
Shear Walls, Infill Walls, Bracings and the designed frame
is a moment resisting frame for the analysis of the building
in these conditions.
Model 1: Stilt+G+4 building models are with and without
floating column at Edge column position, Centre portion
and Parallel positions in Zone 5.
In this model, Normal building frame (i.e. figure 1 and 2)
and building frames with floating column provided in the
first floor at one Edge column position (i.e. figure 3a), at
Centre portion (i.e. figure 3b) and at Parallel column
positions(i.e. figure 3c), are designed and analysed
considering the parameters like maximum displacements
and storey drifts in both X and Y directions and response
spectrum analysis is also observed. When these models are
analysed and compared at zone 5, the obtained results are
tabulated ( i.e. tables 3 and 4),
Model 2: Stilt+G+4 building models are with floating
column with recommendations such as Shear walls, Infill
walls and Steel bracings in Zone 5.
Table 1
Multi-Storey Building Geometrical Dimensions
Member dimensions
Slab Thickness 120mm
Beams
Normal building
230x480mm
Floating column building Varies between
230x480mm to 230x600mm
columns
Normal building 400x400mm
Floating column building Varies between
400x400mm to 600x600mm
Brick infill wall thickness Exterior wall 250mm
Interior wall 150mm
Shear wall thickness 250mm
Loads
Unit weight of concrete 25kN/m2
Unit weight of brick infill 20kN/m2
Floor loads
Live load 3.5
Dead load 1
Roof loads
Live load 1.5
Dead load 1
Grade of rebar
Beams Fe 415
Columns Fe 415

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Table 2
Parameters of Earthquake Loads considered for the Study
Parameters Values
Seismic
zone
factor
Zone 5 0.36
Zone 4 0.24
Zone 3 0.16
Zone 2 0.10
Importance factor 1.0
Response reduction factor 5.0
Percentage of damping 5%
Soil type Medium soil
Table 3
Comparison of Maximum Displacements of the Normal and Floating column building frames, Zone 5
Story Elevation Location NORMAL EDGE CENTRE PARALLEL
Base 0 Top 0 0 0 0
Story1 1.28 Top 0.6 1.4 1 0.4
Story2 4.28 Top 4.9 7 5.4 3.3
Story3 7.28 Top 9.5 11.7 10.1 7.1
Story4 10.28 Top 13.5 15.5 13.8 10.6
Story5 13.28 Top 16.6 18.4 16.8 13.4
Story6 16.28 Top 18.6 20.3 18.9 15.3
Story7 19.28 Top 19.6 21.2 20 16.4
Table 4
Comparison of Maximum Story Drifts of the Normal and Floating column building frames, Zone 5
Story Elevation Location NORMAL EDGE CENTRE PARALLEL
Base 0 Top 0 0 0 0
Story1 1.28 Top 0.6 1.4 1 0.4
Story2 4.28 Top 4.3 5.6 4.4 2.9
Story3 7.28 Top 4.6 4.7 4.7 3.8
Story4 10.28 Top 4 3.8 3.7 3.5
Story5 13.28 Top 3.1 2.9 3 2.8
Story6 16.28 Top 2 1.9 2.1 1.9
Story7 19.28 Top 1 0.9 1.1 1.1

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Table 5
Maximum displacements of the floating column at Edge with the Recommendations, Zone 5
Story Elevation Location INFILL BRACING SHEAR
Base 0 Top 0 0 0
Story1 1.28 Top 2.4 0.1 0.1
Story2 4.28 Top 11.1 0.5 0.6
Story3 7.28 Top 11.2 4.5 1.3
Story4 10.28 Top 11.3 9.2 2.1
Story5 13.28 Top 11.4 13 3
Story6 16.28 Top 11.4 15.6 3.9
Story7 19.28 Top 11.5 16.9 4.7
Table 6
Maximum Storey Drifts of the floating column at Edge with the Recommendations, Zone 5
Story Elevation Location INFILL BRACING SHEAR
Base 0 Top 0 0 0
Story1 1.28 Top 2.4 0.1 0.1
Story2 4.28 Top 8.7 0.4 0.5
Story3 7.28 Top 0.1 4 0.7
Story4 10.28 Top 0.1 4.7 0.8
Story5 13.28 Top 0.1 3.8 0.9
Story6 16.28 Top 0 2.6 0.9
Story7 19.28 Top 0.1 1.3 0.8
Table 7
Maximum displacements of the floating column at Centre with the Recommendations, Zone 5
Story Elevation Location INFILL BRACING SHEAR
Base 0 Top 0 0 0
Story1 1.28 Top 2 0.1 0.1
Story2 4.28 Top 9.1 0.5 0.5
Story3 7.28 Top 9.3 4.3 1.2
Story4 10.28 Top 9.4 8.5 2.1
Story5 13.28 Top 9.5 12.2 2.9
Story6 16.28 Top 9.6 14.8 3.8
Story7 19.28 Top 9.6 16.1 4.6
Table 8
Maximum Storey Drifts of the floating column at Centre with the Recommendations, Zone 5
Story Elevation Location INFILL BRACING SHEAR
Base 0 Top 0 0 0
Story1 1.28 Top 2 0.1 0.1
Story2 4.28 Top 7.1 0.4 0.4
Story3 7.28 Top 0.2 3.8 0.7
Story4 10.28 Top 0.1 4.2 0.9
Story5 13.28 Top 0.1 3.7 0.8
Story6 16.28 Top 0.1 2.6 0.9
Story7 19.28 Top 0 1.3 0.8

5. Disaster Advances Vol. 8 (10) October (2015)
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Table 9
Maximum displacements of the floating column at Parallel position with the Recommendations, Zone 5
Story Elevation Location INFILL BRACING SHEAR
Base 0 Top 0 0 0
Story1 1.28 Top 3.5 0.4 0.1
Story2 4.28 Top 9.5 0.4 0.4
Story3 7.28 Top 9.6 8.2 1
Story4 10.28 Top 9.7 16.1 1.6
Story5 13.28 Top 9.8 22.5 2.3
Story6 16.28 Top 9.8 26.7 3
Story7 19.28 Top 9.9 28.8 3.7
Table 10
Maximum Storey Drifts of the floating column at Parallel position with the Recommendations, Zone 5
Story Elevation Location INFILL BRACING SHEAR
Base 0 Top 0 0 0
Story1 1.28 Top 3.5 0.4 0.1
Story2 4.28 Top 6 0 0.3
Story3 7.28 Top 0.1 7.8 0.6
Story4 10.28 Top 0.1 7.9 0.6
Story5 13.28 Top 0.1 6.4 0.7
Story6 16.28 Top 0 4.2 0.7
Story7 19.28 Top 0.1 2.1 0.7
Fig. 1: Plan view of the normal building Fig. 2: Elevation view of the normal building
a) b) c)
Fig. 3: Plan view of the floating column at a) Edge column position, b) Centre portion and c) Parallel position

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Fig. 4: Comparison of Maximum Displacements of the Normal and Floating column building frames, Zone 5
Fig. 5: Comparison of Maximum Story Drifts of the Normal and Floating column building frames, Zone 5
a) b) c) s
Fig. 6: Elevation view of the floating column building with a) Infill wall, b) Steel Bracings, c) Shear wall
Fig. 7: Maximum displacements of the floating column at Edge with the recommendations, Zone 5

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Fig. 8: Maximum Storey Drifts of the floating column at Edge with the recommendations, Zone 5
Fig. 9: Maximum displacements of the floating column at Centre with the recommendations, Zone 5
Fig. 10: Maximum Storey Drifts of the floating column at Centre with the recommendations, Zone 5

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Fig. 11: Maximum displacements of the floating column at Parallel position with the recommendations, Zone 5
Fig. 12: Maximum Storey Drifts of the floating column at Parallel position with the recommendations, Zone 5
In this model, floating columns are provided in the
first floor at one Edge column position, at Centre portion
and Parallel column positions with recommendations
considered i.e. Infill walls (i.e. figure 6a) and Steel Bracing
system (i.e. figure 6b), Shear walls (i.e. figure 6c), are
designed and analysed considering the parameters like
maximum displacements and storey drifts in both X and Y
directions and response spectrum analysis is also
observed. When these models are analysed and compared
at zone 5, the obtained results are tabulated (i.e. table 4 to
10), shown the graphical representation (i.e. figures 7 to
12).
Conclusion
This study mainly comprises the difference between a
Normal column building and a Floating column building
and then followed with the recommendations for a safe and
economical design of a floating column building which can
be defined as an earthquake resistant design i.e. to resist
against the disaster like earthquakes and following
conclusions are drawn from the analysis:
1) In the present study, it is observed that the Normal
column building is more efficient having allowable
displacements and storey drifts when compared with other
models i.e. floating column buildings.
2) Similarly, when the floating column models are
compared with each other, it is observed that the floating
column building at one Edge column position has higher
displacements and storey drifts followed by floating column
at Centre portion and finally the floating column at the
parallel positions.
3) The introduction of floating columns in the RC frames
increases the time period of bare frames due to decrease in
the stiffness.
4) It is observed that the models provided with
recommendations show the allowable deformation limits
when analysed, where the floating column building models
without recommendations are beyond the deformation limits
as per IS codes.
5) When the recommendations are considered, Shear walls
show efficient resistance to the natural disaster effects such
as earthquake forces exerted on the frame when compared
with Infill walls and Bracings.
6) Finally, it is concluded that the floating column building
will lead to the increase in dimensions of the members
in the structure to increase the stiffness considerably
increase the cost of construction also.

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7) It is concluded that the floating column buildings can be
preferably constructed for disasters i.e. like earthquakes
with earthquake resistant design criteria for the architectural
and site situations but with careful analysis and guidance.
References
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Different Shapes of Shear Walls in Unsymmetrical High Rise
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Building With and Without Floating Column, International
Journal of Current Engineering and Technology, 4(5) 3395-3400
(2014)
3. Bureau of Indian Standards: IS-1893, Part 1, Criteria For
Earthquake Resistant Design of Structures: Part 1, General
Provisions and Buildings, New Delhi, India (2002)
4. Bureau of Indian Standards: IS-13935-1993, Repair and
Strengthening of Buildings”, New Delhi, India (1993)
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(Received 15th
July 2015, accepted 30th
August 2015)
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