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A column is a vertical member which transfers the loads from beam to foundation whereas a floating column is a vertical member which transfers the load from beam to another beam. The load transfer in any building is usually from slab to beams to columns and then foundation. But a floating column, instead of transferring the load to foundation transfers the load on to the beam. The beam on which the floating column rests transfers the load to the columns below. The load is transferred in the form of a point load.
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.
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.
Floating Column and 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.
Floating columns, though highly discouraged, are still an important part of the construction industry. It is in our hands to ensure correct analysis and design of this structural member. It is our responsibility to ensure that the detailing of this structural member and the girder beam supporting this floating column is done properly.
With all its advantages and disadvantages, a floating column is one of the favorite structural elements in today's construction world.