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IJSRD - International Journal for Scientific Research & Development| Vol. 4, Issue 05, 2016 | ISSN (online): 2321-0613
All rights reserved by www.ijsrd.com 219
Seismic Analysis of Multistorey Building with Floating Columns Ashish. G. Pakmode1 Prof. Lakshmikant Vairagade2
1M.Tech. Student 2Assistant Professor 1,2Department of Civil Engineering
1,2Institute of Technology, University of Gondar, EthiopiaAbstract— The objective of the present work is to study the
behavior of multistorey buildings with floating columns
under earthquake excitations. Finite element method is used
to solve the dynamic governing equation. Linear time history
analysis is carried out for the multistorey buildings under
different earthquake loading of varying frequency content.
The base of the building frame is assumed to be fixed.
Newmark’s direct integration scheme is used to advance the
solution in time. The project is aimed at arriving to suitable
configuration, modeling, developing models for analysis and
design of building with floating column. A through study of
relevant specifications is also aimed in the project. STAAD
PRO version 8 is used for analysis and design.
Key words: Floating Column, Multistorey Buildings,
STAAD PRO
I. INTRODUCTION
Many metropolitan cities multistorey buildings in India
today have open first storey as an unavoidable feature. This
is primarily being adopted to hold parking or reception
lobbies in the first storey. Whereas the total seismic base
shear as veteran by a building during an earthquake is reliant
on its natural period, the seismic force distribution is reliant
on the distribution of stiffness and mass along the height.
The behavior of a building during earthquakes
depends critically on its general shape, size and geometry, in
addition to how the earthquake forces are carried to the
ground. The earthquake forces developed at divergent floor
levels in a building need to be brought down along the
height to the ground by the shortest pathway; any deviation
or discontinuity in this load transfer path results in poor
performance of the building. Buildings with erect setbacks
(like the hotel buildings with a few storey wider than the
rest) cause a abrupt jump in earthquake forces at the level of
discontinuity. Buildings that have less columns or walls in a
particular storey or with oddly tall storey tend to break or
collapse which is initiated in that storey. Many buildings
with an open ground storey proposed for parking collapsed
or were severely damaged in Gujarat during the 2001 Bhuj
earthquake. Buildings with columns that suspend or float on
beams at an intermediate storey and do not go all the means
to the foundation have discontinuities in the load transfer
path.
A. What is an earthquake?
Earthquakes are defined as a sudden vibration of the earth's
surface that occurs after a release of energy in the earth's
crust. Since the earth's crust is made up of several plates that
are constantly moving slowly, vibrations can happen which
result in small earthquakes. The majority of earthquakes are
small but are not eagerly felt. Superior and aggressive
earthquakes are those which occur in a discharge of energy
as the plates slide past or crash into one another. The
characteristics such as strength, period, etc. of seismic
ground shakes estimated at any location depend upon the
earthquake’s magnitude, its focus depth, distance from the
epicenter, characteristics of the pathway through which the
seismic waves moves, and the soil strata on which the
constructed structure stands. The major direction of ground
vibration is usually flat or horizontal.
Fig. 1: Earthquakes
Reinforced concrete Special moment frames are
used as fraction of seismic force resisting systems in
buildings that are planned to resist earthquakes. Beams and
columns in moment frames are proportioned and detailed in
such a manner that they must oppose flexural, axial, and
shearing actions that effects as a building sways through
multiple displacement cycles during strong earthquake
ground shivering. Special proportioning and detailing
requirements are liable for frame, competent of resisting
strong earthquake shaking without important loss of
stiffness or strength. These moment-resisting frame is called
as “Special Moment Frame” cause of these additional
necessities, which improve the seismic resistance in contrast
with less severely detailed Intermediate and Ordinary
Moment Frames.
B. What is column?
A column is supposed to be a vertical part of a building
starting from foundation level and transferring the load to
the ground.
Fig. 2: Column
C. What is a Floating Column?
The term floating column is also a vertical part of a building
which (due to architectural plan/ site conditions) at its lower
level or Termination Level rests on a beam which is a
horizontal part. The beams in turn transmit the load to other
columns below it.
Seismic Analysis of Multistorey Building with Floating Columns
(IJSRD/Vol. 4/Issue 05/2016/056)
All rights reserved by www.ijsrd.com 220
Fig. 3: Hanging or Floating Columns
There are a lot of projects in which floating
columns are adopted, mainly above the ground floor, where
transfer girders are employed, so that extra open space is
available in the ground floor. These open spaces may be
necessary for assembly lobby or parking purpose. The
transfer girders have to be planned, designed and detailed
properly, mainly in earthquake zones. The column is an
intense load on the beam which supports it. As far as
analysis is concerned, the column is often assumed pinned at
the base and is consequently taken as a point load on the
transfer beam. Floating columns are capable enough to take
gravity loading but transfer girder must be of sufficient size
(Stiffness) with very minor deflection.
Looking further, of course, one will continue to
make buildings attractive rather than repetitive. However,
this need not be done at the cost of poor performance and
earthquake safety of buildings. Architectural features that
are unfavorable to earthquake reaction of buildings should
be avoided. If not, they must be minimized. When irregular
features are incorporated in buildings, a significantly higher
level of engineering effort is required in the structural design
and so far the building may not be as good as one with
simple architectural features. Hence, the structures already
finished with these kinds of discontinuous members are rare
in seismic regions. But those structures cannot be
demolished, rather study can be completed to strengthen the
structure or some corrective features can be suggested. The
columns of the primary storey can be made stronger, the
rigidity of these columns can be increased by retrofitting or
these may be provided with bracing to reduce the lateral
deformation.
II. OBJECTIVE AND SCOPE
To Analyze the behaviour of building for various
floating combinations by dynamic analysis.
To compare normal and floating column building with
parameter such as the displacement by considering I.S
code loading and load combination.
III. MODELING AND ANALYSIS
The building considered in the present report is G+6
storied R.C framed building of symmetrical
rectangular plan configuration. Complete analysis is
carried out for dead load, live load & seismic load
using STAAD PRO. Response spectra method of
seismic analysis is used. All combinations are
Considered as per IS 1893:2002.
Typical plan of building is shown in Fig.3.1
Fig. 4: Plan of G+ 6 structures
A. Building Properties
1) Site Properties
Details of building:: G+6 RC structure
Outer wall thickness:: 230mm
Inner wall thickness:: 230mm
Floor height ::3 m
Height of parapet wall ::0.8 m
Thickness of parapet wall:: 230 mm
2) Seismic Properties
Seismic zone:: II
Zone factor:: 0.1
Importance factor:: 1.5
Response Reduction factor R:: 3
Soil Type:: medium
Material Properties
Material grades of M25 & Fe415 were used for the
design.
B. Loading on Structure
Dead load: self-weight of structure
Weight of 230mm wall: 14.25 kN/m²
Weight of parapet wall: 3.5 kN/m²
Live load: 4 kN/m²
Roof Live load: 1.5 kN/m²
Wind load: Not considered
Seismic load: Seismic Zone II
C. Preliminary Sizes of Members
Column:: 450mm x 600mm
Beam:: 250mm x 400mm
Slab thickness:: 125mm
D. Model Type
Type I: No float.
Type II: float type I
Type III: float type II
Type IV: float type III (mix of Type I & II).
1) No Float
Seismic Analysis of Multistorey Building with Floating Columns
(IJSRD/Vol. 4/Issue 05/2016/056)
All rights reserved by www.ijsrd.com 221
Fig. 5: No Float
2) Float 1
Fig. 6: Float 1
3) Float 2
Fig. 7: Float 2
4) Float 3
Fig. 8: Float 3
IV. RESULTS
The results are obtained and presented in terms of critical
structural response such as displacement in the building
structure with and without float Models due to the applied
seismic or earthquake load. The variations of the critical
structural response for column C1, C5, C9 & C13 due to I.S
code load combinations are presented below.
Seismic Analysis of Multistorey Building with Floating Columns
(IJSRD/Vol. 4/Issue 05/2016/056)
All rights reserved by www.ijsrd.com 222
Seismic Analysis of Multistorey Building with Floating Columns
(IJSRD/Vol. 4/Issue 05/2016/056)
All rights reserved by www.ijsrd.com 223
Seismic Analysis of Multistorey Building with Floating Columns
(IJSRD/Vol. 4/Issue 05/2016/056)
All rights reserved by www.ijsrd.com 224
Fig. 9: Results
V. DISCUSSIONS
Parametric study is carried out on Building structure with &
without floating columns for various I.S code load
combinations using Staad Pro. In this paper the change in
displacements of selected columns i.e. C1, C5, C9 & C13
are compared. The results obtained for C1, C5, C9 & C13
are presented in the form of graphs.
VI. CONCLUSIONS
The comparative study for the various columns
combinations i.e. C1, C5, C9 & C13 is done for various load
combinations given in I.S code. It has been seen that in the
load combinations where seismic or earthquake loadings are
not present the displacement of structure having no floating
columns is comparatively less than the structure having
floating columns. On the other hand where the earthquake or
seismic load are present in the combinations given in I.S
code the displacement of no float structure is comparatively
greater than the structure having floating columns.
ACKNOWLEDGMENT
The journalist would like to prompt their sincere thanks to
the G.H.R.A.E.T college of Engineering for giving
Guidance and technical support to get done this research.
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