What is Column | Planted Columns |Floating Column or Hanging Columns
What is Column?
A column can be defined as a vertical structural member which transmits the loads from beam of the building to foundation. Columns are the essential compression structural members which transfer the loads from the top structural level to the lowers passing through the foundations. A column is one of the crucial structural members.
What is a Planted Column?
A planted column is a vertical compression member supported on a non-axial bearing member (member designed to withstand force in a perpendicular direction) such as slabs or beams to provide the structural requirements without sacrificing interior and architectural needs.
However, only a few studies about the behaviour of planted columns and the supported beam may not be advisable.
Floating Column or Hanging Columns
What is Floating Column?
A floating column acts as a point load on the beam, and this beam transmits the load to the columns below it.
The column may start on the first or second or any other intermediate floor while resting on a beam. Typically, the columns rest on the foundation to transfer load from slabs and beams; however, the floating column rests on the beam.
It is designed as a standard compression structural member over the beam or slab, and the beam below the floating column is intended to be load transfer beam, in which beam takes the load of the floating column as a point load.
The beam designed to support the floating column is done with high shear capacity or as deep beams.
The system is so designed that the stub column is not the part of the lateral load resisting system (Earthquake and wind loads). The floating column is analyzed in software by providing pin joints at the ends.
Floating Column Design
Why Floating Columns are not Advisable
The floating column designs can be a dangerous practice used by many structural designers is found undesirable for the following reasons.
They are constructed over the beam, and hence it won’t be having any form of continuity with the structural elements below it.
A floating column forms one of the essential main structural members of a structure but can attract large seismic forces in seismic prone regions or during earthquakes.
A floating column can make every floor different, with the other grid system and will affect vertical symmetry of the building. The structure will have poor performance when subjected to earthquake forces.
Using floating columns in buildings increases the storey displacement and storey drift under the action of lateral force.
With a floating column base shear created at the building support during earthquake activity is high.
This floating column tends to increase the base shear and story displacement of buildings under earthquake action, and it is not a desirable performance. Therefore, past performance of the floating column in seismic prone regions make them unsuitable in future construction. They are limited to support gravity loads alone.
Advantages of Floating Columns
- A Floating column is primarily used to fulfil the architectural requirements of a building. Floating columns are significant when the lower floor has a large span hall having rooms on its upper floor like hotel or auditorium
- Floating columns are useful in the construction of soft storeys.
- The plan layout on every floor can be different
- The rooms can be partitioned, and some portion can be raised without raising the whole area.
Disadvantages of Floating Column
- · The primary disadvantage of floating columns is that it often suffers during the earthquake and when subjected to major seismic movements. Beams supported by floating columns may experience a large amount of bending, shear forces and tension forces. However, this problem can be reduced but still not advisable in case of lateral loading.
- · Floating columns attracts extensive forces.
- · Floating columns increases storey displacement in structures.
- · Because the floating columns do not rest on primary continuous columns, discontinuity happens with the below and above columns, making it vulnerable.
As a structural engineer, we advise against the provision of floating columns in a building structure. Architects may not be aware of its implications, as the floating columns are more vulnerable to seismic forces. Always opt for an alternate solution.