Jacketing of column is the method of adding transverse and longitudinal reinforcement around the existing columns in a building. The main advantage of column jacketing is that it increases the load capacity of the building by distributing the weight uniformly.
Jacketing is the most popular and common method of earthquake retrofitting RCC buildings. Different types of jackets are reinforced concrete jacket, steel jacket, fiber reinforced polymer composite jacket, jacket with high-tension materials like glass fiber, carbon fiber, etc.
The advantages of jacketing include increase in concrete confinement, especially for circular columns, increase in shear strength (strength against sliding failure), and flexural strength (resistance to bending or deformation).
By method of jacketing, strengthening of foundation can be avoided. As there will not be any major changes to the geometry of the structure, the building can be put to its original function.
Reinforced Concrete Jacketing
In some cases, we may need to eliminate or reduce the loads acting on the column before jacketing. This can be achieved either by installing mechanical jacks between the floors or by using additional props between the floors.
Jacketing of column is started by digging holes into the existing column to insert the steel connectors to hold the stirrups. The steel connectors are held in position by filling the holes with epoxy material.
Similarly, vertical steel connectors are installed to hold vertical bars, and the vertical bars and stirrups are installed next. The existing column is coated with an epoxy material for bonding and concrete is poured into the jacket.
This method is adopted when it is not possible to increase the area of the column and when load acting on the column increases. Steel jacketing procedure starts with removing the concrete cover and cleaning the steel bars with sand compressor or wire brush. Steel bars are coated with a corrosion repelling epoxy material.
Steel jacket is installed to the structure with enough openings to insert the epoxy material, which provides bonding between the steel jacket and concrete column. Then the space in-between is filled with the epoxy material.
Both reinforced concrete jacketing and steel jacketing procedure needs to be carried out under proper supervision. Jacketing is a very effective method of strengthening columns and the increase in strength is considerably higher than the original column.