Floating columns are vertical members that rest on beams but do not directly transfer loads to the foundation. They act as point loads on beams, which then transfer the load. Floating columns are used to alter floor plans but are undesirable for lateral earthquake forces as they disrupt force transfer paths. While they provide flexibility, floating columns increase displacement and attract seismic forces. Modern codes prohibit floating columns for high-rise buildings in seismic zones due to past building collapses where their presence led to soft stories and irregularities.

1. FLOATING
COLOUMN

2. o Floating coloumn
The floating column is a vertical member which rest on a beam but doesn’t
transfer the load directly to the foundation. The floating column acts as a point load on
the beam and this beam transfers the load to the columns below it. The column may
start off on the first or second or any other intermediate floor while resting on a beam.
Usually columns rest on the foundation to transfer load from slabs and beams. But the
floating column rests on the beam.
This means that the beam which supports the column acts as a foundation.
That beam is called as a transfer beam. This is widely used in high
storied buildings for both commercial and residential purpose. This helps to alter the
plan of the top floors to our convenience. The transfer beam which supports the
floating column, transfers the loads up to foundation. Hence this has to be designed
with more reinforcement.

3. o Floating Column in Buildings
Now a days multi-storey buildings constructed for the purpose of residential,
commercial, industrial etc., with an open ground storey has become a common feature.
For the sake of parking, the ground storey is kept free without any constructions, except
for the columns which transfer the building weight to the ground. For a hotel or
commercial building, where the lower floors contain banquet halls, conference rooms,
lobbies, show rooms or parking areas, large interrupted space is required for the
movement of people or vehicles. The columns which are closely spaced in the upper
floors are not advisable in the lower floors. So to avoid this problem,
floating column concept has come into existence.

4. In urban areas, multi storey buildings are constructed by providing floating columns at
the ground floor for the various purposes which are stated above. These floating
column buildings are considered safe under gravity loads and hence are designed only
for those loads. But these buildings are not designed for earthquake loads and
therefore, these buildings may be unsafe in seismic prone areas. When the floating
columns are employed in buildings in seismic prone areas, the entire earthquake of the
system is shared by the column or the shear walls without considering any contribution
from the floating columns.

5. o Floating Column & Earthquake
The lateral forces due to earthquake need to be transferred to the foundation
through clear force transfer path. This force transfer path is disrupted in case of
floating columns. These floating columns attract a lot of seismic force, which is
unfavorable in the high seismic zone.
The floating columns act well when only vertical forces are considered. But they are
highly undesirable for lateral forces such as earthquake. It is highly discouraged to
have floating columns in high seismic zone regions.
But even then, we see a lot of buildings be it residential, commercial or
industrial using floating columns in their construction. And the only reason being the
flexibility to alter the plan above or below to suit the client requirement. This is where
our knowledge and art of structural engineering comes into play.
So, in this situation, it is the job of structural engineers like us to ensure that
such buildings are not only analyzed properly but the detailing of such buildings is
also done properly. Detailing of the steel becomes a crucial part of floating column
construction.

6. o Need of Floating Column
Now a days multi-storey building construction for residential, industrial or
commercial purpose has become a common feature. These multi-storey building need
ample of parking or open spaces below.
In multi-storey residential building to accommodate for the number of
parking places and the turning radius, some of the columns from the floors above
create a problem. In these cases, these columns are designed as floating columns.
Even in commercial building there might be a need for conference hall or
banquet hall on the lower floors. For these purposes we prefer to have a clear open
space rather than having columns in between. This is where floating columns come
into the picture. Floating columns gives the liberty to alter the floor plans above.

7. o How are Floating Columns Incorporated in the
structure?
Like in any structure, the load from the floors above is transferred to the
column. The entire load is then transferred to the beam on which the floating
column is going to rest. The floating column is designed as regular column. The
beam on which it rests is designed as a beam carrying all the load of the column as
a single point load.
This beam referred to as girder beam or transfer beam usually has a big
cross section with heavy steel. This girder beam is also subjected to torsion. The
design and detailing of this girder beam is very crucial in the construction of
floating columns.

8. o Load Transfer in Floating Columns and Non-floating
Columns
The load transfer is directly done by the non-floating column where it is
safely transferred to the foundation.
In case of floating column, the load is taken by the below beam. The
column is arranged as a point load over the beam. The load is equally distributed to
the beam.
o Advantages and Disadvantages of Floating Column
The floating column is undesirable in building construction. Some of
the reasons are:
1.Increased storey displacement in buildings
2.Attract seismic forces extensively
3.There is no continuity with the above and below floors making it
vulnerable
Still floating column is used due to following advantages
1.The plan can be varied on each floor
2.Construction of Soft-storeys
3.Architectural Importance

9. o Why People or Architects take Floating Columns?
In modern times the buildings are becoming complex particularly the mix
use ones. There are different uses on different floors and hence to follow it
structural grid becomes difficult as columns on any floor would become a
hindrance. Even in residential buildings when there is a parking on ground floor or
lower stories or huge cantilevers are taken to exploit ambiguities in Local bye-laws
for gaining more FSI, the lower floors need column-free spaces for easy movement
of vehicles; while on upper floors which are more in no, the columns have been
designed based on room layout. They are also frequently used when there are shops
on ground floor and residence on upper floors. Rather than finding an architectural
solution one easily take recourse to floating columns and remove columns on lower
stories, which is “a dangerous proposal”.
Those architects who are not able to find design solutions in their design
or those who do not respect the structural engineering and force the structural
engineer to alter the uniform vertical alignment of columns and to provide floating
columns. What has happened during last few years is that; that someone took a risk
and the building survived and hence architects and structural engineers thought that
this could be done. Hence now this practice has reached a stage where it is followed
by many in violation of all norms. People do not understand that the building has
survived in Gravity loads only. But they forget that how it would behave in
Earthquake or wind i.e. when subjected to horizontal loads.

10. They also forget that earthquake occurs once in a life of building i.e. once in 50
or 100 years and at such times it might prove absolutely fatal. In our opinion
taking floating columns is not a sound engineering practice.

11. o Floating Column Applications
The most important application of floating column is for the construction of
soft storey in the ground floor to facilitate free space for parking or entrance
corridors. This free space will provide parking option for residential, industrial and
commercial buildings.
In banquet halls, lobbies, conference room, large interrupted column free
space is required for free movement of people and vehicles. This must avoid closely
spaced columns in the area. A wrong practice that has come into force is to solve such
problems by providing floating column.
Floating columns are constructed to obtain different grid arrangement in
different floors.

12. The floating column is designed as a normal compression member over the
beam or slab. The beam below the floating column is designed as transfer beam, where
the beam carries the load of the floating column as a point load. The beam that is
employed to support the floating column is designed with high shear capacity or as deep
beams. These provisions are not stated in Indian codes. The system is so designed that the
stub column is not the part of lateral load resisting system (Earthquake and wind loads).
The floating column is analyzed in software by providing pin joints at the ends.

13. Plan of G+2 building

14. FLOOR NAME COLOUMN NO.
SIZES
WIDTH DEPTH
GROUND FLOOR
C1,C4,C28,C23 400mm 230mm
C6,C7 450mm 230
FIRST FLOOR
C1,C4,C28,C23 240mm 230mm
C2,C12,C16,C18,C28,
C17,C13,C21
270mqm 230mm
C5,C6,C7,C10 350mm 230mm
SECOND FLOOR
C1,C4,C28,C23 220mm 230mm
C2,C3,C12,C14,C16,
C18,C20,C24,C28,C27,
C26,C21,C19,C17,C13
240mm 230mm
C5,C6,C7,C10,C11,C22
310mm 230mm
SIZES OF COLOUMN:-

15. REINFORCEMENT OF COLOUMN:-
FLOOR NAME COLOUMN NO.
COLOUMN BAR
TRANSVERSE
REINFORCEMENT
No. of
bars
Dia of
bars
Dia of bar distance
GROUND FLOOR
C1,C4,C28,C23 10 14 8 190 c/c
C6,C7 10 14 8 170 c/c
FIRST FLOOR
C1,C4,C28,C23 10 12 6 190 c/c
C2,C12,C16,C18,C28,
C17,C13,C21
10 12 6 190c/c
C5,C6,C7,C10 10 12 6 180 c/c
SECOND FLOOR
C1,C4,C28,C23 8 12 6 190 c/c
C2,C3,C12,C14,C16,
C18,C20,C24,C28,C27,
C26,C21,C19,C17,C13
8 12 6 185 c/c
C5,C6,C7,C10,C11,C22
,C23
8 12 6 195 c/c

16. FLOOR BEAM NO.
SIZE
REINFORCEMENT
d b
GROUND FLOOR
B1,B2,B3,B4,B5 300 230
Provide 10mm dia. 2
legged stirrups at
100mm c/c
B6,B7,B8,B9,B10 320 230
Provide 10mm dia. 2
legged stirrups at
95mm c/c
FIRST FLOOR
B1,B2,B3,B4,B5
320 230
Provide 10mm dia. 2
legged stirrups at
110mm c/c
B6,B7,B8,B9,B10
300 230
Provide 10mm dia. 2
legged 100stirrups at
mm c/c
SECOND FLOOR
B1,B2,B3,B4,B5
300 230
Provide 10mm dia. 2
legged stirrups at
110mm c/c
B6,B7,B8,B9,B10
310 230
Provide 10mm dia. 2
legged stirrups at
105mm c/c
BEAM REINFORCEMENT:-

17. FOOTING NO.
SIZE
Development
length(mm)
REINFORCEMENT
D(mm) B(mm)
C1,C2,C6,C5 450 310 1385
Provide 16mm dia.
Bars at 105mm c/c on
both side
C3,C4 430 300 1240
Provide 16mm dia.
Bars at 150mm c/c on
both side
Design of footing:-

18. o Are Floating Columns Advisable?
The floating column construction, a dangerous practice adopted by many
structural designers is found undesirable due to the following reasons.
• They are:
1.Floating column is constructed over the beam and hence it won’t be having
any form of continuity with the structural elements below.
2.Floating columns can make every floor different, with different grid
system. This will affect vertical symmetry of the building. This will affect the building
performance during earthquake forces.
3.This forms one of the critical elements in the building, which will attract
large seismic forces in seismic prone regions or during earthquakes.
4.Using floating columns increases the story displacement and story drift
under the action of lateral force.
5.The base shear created at the building support during earthquake activity is
high.
6.The floating column tends to increase the base shear and story
displacement of buildings under earthquake action. This is not a desirable
performance. Hence, past performance of floating column in seismic regions make
them unsuitable in future construction. They are limited to take up gravity loads alone.
7.During Bhuj Earthquake (Jan 26, 2001) many multi storied buildings
collapsed like pack of cards within seconds, as there were presence of soft stories,
floating columns and mass irregularities.

19. As per the 6th revised edition of IS: 1893 – 2016 (Part 1) – Clause 7.1, it
is not recommended to have floating columns in building construction.
FLOATING COLUMNS AS PER THIS CODE ARE NOW
PROHIBITED. Hence floating columns not being a sound engineering
practice do not recommend it, especially for high-rise structures.