A floating column is a vertical column that does not have a direct connection to the foundation below it, but instead, it is supported by a beam.
These columns are used in multistory buildings where changes in floor levels or other architectural features make it difficult to connect the column directly to the foundation.
Floating column guidelines as per IS 456 and IS 1893
As per the Indian Standard Code of Practice for Design of Reinforced Concrete Structures (IS 456:2000), a floating column is a vertical column that is not directly connected to the foundation below it but instead rests on a beam.
As per IS 1893-2016 Part 1 (Table 6 VI Page 16) the use of floating columns should be avoided wherever possible, as they may cause concentrated damage to the structure in the event of an earthquake or other lateral forces.
If a floating column is necessary, the following guidelines should be followed:
- This column should be designed to resist all vertical and horizontal loads acting on it.
- The beam supporting this column should be designed to resist the vertical and horizontal loads transmitted by the floating column.
- Adequate provision should be made to ensure that the beam does not fail due to the excessive deflection of the floating column.
- The size and location of this column should be such that it does not cause any adverse effect on the stability and safety of the building as a whole.
Load transfer mechanism in floating column
In a building structure, the load transfer in this type of column is different from that of a traditional column that is directly connected to the foundation.
When a load is applied on top of a floating column, it is transferred to the beam or slab directly underneath the column.
The beam or slab is responsible for distributing this load to the adjacent columns or walls in the building. This is known as the load transfer mechanism.
Advantages
Architectural flexibility
It allows for more architectural freedom and creativity in building design, as they can be used to create unique and interesting architectural features, such as cantilevers, mezzanines, and split-level floors.
Reduced construction costs
It can reduce construction costs by eliminating the need for complex foundation designs and deep excavations. This can be especially beneficial in areas with difficult soil conditions, where it may be more costly to construct traditional foundations.
Increased space utilization
It can help to maximize the use of available floor space by reducing the amount of space taken up by structural elements.
Disadvantages
Structural integrity
It can compromise the structural integrity of a building if not properly designed and installed.
This is because they do not directly transfer the loads to the foundation, which can lead to concentrated stresses on the beam and column system and can cause damage during lateral loads such as earthquakes or wind.
Limited load capacity
It typically has limited load-carrying capacity compared to traditional columns, which can limit their use in certain types of buildings and structures.
Reasons for floating column failure
- Inadequate design of the floating column or load transfer mechanism
- Inadequate strength of the beam or slab to hold the load of the floating column
- Insufficient reinforcement of the column or beam/slab
- Use of poor-quality materials
- Structural overloading due to changes in building usage or occupancy
- Incorrect installation or construction methods
- Excessive deflection or movement of the floating column due to external forces or environmental factors
- Seismic activity or natural disasters
- Check the alignment of these columns to ensure it is in the correct position and orientation.
- Check all the rebar, ties, and spacing details as per the drawings
- Check clear cover is provided as per the structural drawing.
- Determine the anchoring requirements for the column, including the type and number of anchors needed to secure the column in place. (In short check the formwork)
