Seismic Analysis of Multistorey Building with Floating · PDF filedesign of building with floating column. ... STAAD PRO version 8 is used for analysis and design. Key words: Floating

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)


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




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.










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.

REFERENCES

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Seismic Analysis of Multistorey Building with Floating · PDF filedesign of building with floating column. ... STAAD PRO version 8 is used for analysis and design. Key words: Floating