The required load-carrying capacity of columns damaged due to earthquake can be regained by retrofitting the inclined columns. During earthquakes, the top and bottom parts of a column are most vulnerable to shear forces. If the forces are large, the column may lose most of its strength and may get inclined under seismic and vertical loads, see Figure-1.
The process explained in this article is ideal for retrofitting inclined columns. The retrofit process for columns damaged at the top involves estimating loads on damaged columns, jacking beams supported by the column, removing deteriorated concrete and deformed steel bars, installing reinforcements, and assembling formwork and pouring concrete. The concrete should be cured adequately after formwork removal.
How to Retrofit Inclined Columns Damaged at the Top Due to Earthquakes?
1. The first step is to jack up deflected beams that support the damaged column to restore the level and release loads on the column to a certain extent. Adjustable jack posts or any other suitable means can be used to lift the beams.
2. The load on the jack posts should be estimated to determine the required number of jack posts needed for the work. The lifting capacity of the jack posts is commonly known and provided by the manufacturer.
3. Set up jack posts at proper places to avoid hindering the repair process.
4. Restore the beam to a required level using jack posts after they have been placed at their position, see Figure-3. If the lifting process is difficult, one can remove concrete from the column, cut deformed reinforcement, and then continue the lifting process.
5. After the required level is reached, remove the concrete from the lower part of the beam to improve the joint reinforcement detail.
6. Place new column reinforcement and splice them with the existing ones. The length of the splice between existing and new reinforcement should be at least 40d. Rearrange and add stirrup if necessary.
7. Place and assemble the formwork. If concreting is difficult, create a hole in the floor slab to facilitate the concrete pouring process.
8. Pour concrete and consolidate it properly.
9. Finally, remove formworks and cure the concrete properly till it gets adequate strength.
The above procedure is considered for columns damaged at the top. If the bottom of the column is damaged, a similar process is to be followed. The reinforcement of the column should be extended into the footing and detailed correctly.
It is the process of reconstruction and renewal of structural concrete elements like columns, beams, slabs, walls, etc. Retrofitting involves determining the origin of distress, removing damaging materials, and selecting suitable repair material and repair techniques.
The purpose of retrofitting is to regain load-carrying capacity of damaged member and increase its life span or increase the ultimate load carrying-capacity when an increase in the imposed load is expected due to variations in the function of the building.
Concrete columns may get damaged and inclined due to seismic forces. This type of column can be retrofitted by releasing the load on the column, remove damaged concrete and deformed bars, installing new bars, pouring concrete into preassembled forms, and finally curing the concrete to achieve adequate strength. After that, the column can be loaded.
Steps for Concrete Damage Repair in Reinforced Concrete Structures
Methods of Strengthening Concrete Columns
Jacketing and Collars for Concrete Column Beam Strengthening