Repair of Concrete Columns for Cracks and Damages
In order to commence the repair of a concrete column, it is imperative to have knowledge of several crucial factors such as the axial dead load, axial live load, horizontal load, and their associated moments. These parameters are essential for determining the extent of the damage and the level of restoration required.
Concrete column repairs can be broadly classified into two categories based on the nature of the damage. The first category is surface or cosmetic repair, which is limited to addressing localized deterioration in the structure. The second category is structural repair, which involves restoring or strengthening the affected columns.
If the deterioration in the concrete column does not significantly reduce the cross section, conventional concrete repair techniques can be effectively utilized. These techniques involve using materials and methods that restore the structural integrity of the column without altering its dimensions or load-bearing capacity. This type of repair is considered a cost-effective solution for addressing minor damages and maintaining the longevity of the structure.
Methods of Concrete Column Repair for Damages and Cracks
Columns may be repaired by using one or more of the following methods:
There are several methods that can be used to strengthen and protect reinforced concrete columns. One approach is to encase the column with additional materials, such as concrete or steel plates, to increase its cross-sectional area. This process, also known as jacketing, can enhance the column’s load-carrying capacity and improve its resistance to external forces.
Another technique is to apply cathodic protection to the reinforcing steel within the column. By introducing an electrical current to the steel, this method can stop or slow down the corrosion process, which can weaken the structure over time.
Re-alkalization is another method that can be used to halt the corrosion of reinforcing steel in a column. This process involves applying a highly alkaline solution to the steel, which can neutralize the acidic environment that causes corrosion to occur.
Chloride extraction is another approach to preventing corrosion in reinforced concrete columns. This method involves removing chloride ions from the concrete, which can help slow down or stop the corrosion of the reinforcing steel.
Confinement is another method that can be used to strengthen a reinforced concrete column. This technique involves wrapping the column with steel plates, carbon fiber, or glass fiber materials to improve its load-carrying capacity and resistance to external forces.
In situations where the shear capacity of intermediate floors is insufficient, the addition of shear collars can be a helpful solution. These collars can increase the shear capacity of the floors and prevent structural failure.
To increase the moment capacity of a reinforced concrete column, a steel plate assembly can be added. This assembly can provide additional strength and support to the column, which can enhance its overall load-carrying capacity.
Supplemental columns can also be added to reinforce a structure. These columns can help distribute the load across the structure more evenly and improve its overall strength.
Finally, applying a protection system can help prevent future corrosion and damage to reinforced concrete columns. By implementing a protective coating or other measures, the column can be shielded from external factors that may cause it to deteriorate over time.
Following parameters are important for the design and the execution of the column repair:
Unloading Columns
Significant deterioration in a column may require unloading it before repairing it. This is necessary so that the entire cross section of the repaired column can carry the design load once again. If the column is not unloaded, the new repair will not be able to bear much load. Furthermore, the drying shrinkage of the new material used for the repair can further reduce its load-bearing capacity. However, unloading columns can be challenging and expensive, particularly in tall buildings. If the existing load on a column is not removed before repairing it, the jacket used for repair will only serve to confine the existing column, and its ability to bear direct load will be minimal – usually less than 25% of the jacket strength.
In situations where unloading a column is not feasible, a supplemental column system can be used to provide an alternative method of support in combination with the repair of the existing column. By using a supplemental column system, the load can be redistributed, and the repaired column can be brought back to its original load-carrying capacity. This method involves using a separate column that is designed to carry a portion of the load from the damaged column. The supplemental column is usually installed next to the damaged column and attached to it with steel plates or bolts. The supplemental column is then braced to ensure that it can carry its share of the load effectively.
In summary, repairing columns that have suffered significant deterioration can be a challenging task, particularly when unloading the column is not feasible. If the existing load on the column is not removed before repairing it, the jacket used for repair will not be able to carry much load, and its effectiveness will be limited. In such cases, using a supplemental column system can provide an alternative method of support, allowing the load to be redistributed and the damaged column to be repaired to its original load-carrying capacity.
Redistribution of the Load
When reinforcement corrosion and concrete deterioration occur in a structure, it can lead to a redistribution of load throughout the entire system. This new pattern of load distribution must be carefully considered when designing repairs. It is not enough to simply repair the damaged areas without taking into account the potential effects on the entire structure.
Furthermore, the impact of the load redistribution may not be limited to the immediate area of the damage. Adjoining members may also have been affected and may need to be taken into account during the repair process. Failing to address the full extent of the damage can result in further deterioration and potential safety hazards.
Therefore, it is important to thoroughly assess the extent of the damage and the resulting load redistribution before beginning any repairs. By doing so, engineers can design effective repairs that address the full scope of the problem and ensure the safety and integrity of the entire structure.
Supplemental Reinforcing Steel
During the repair of a column, it is important to avoid disturbing the ties as it can result in buckling of the longitudinal bars. This means that the original cage of ties cannot be moved. However, supplemental vertical bars can be added to the outside of the cage with additional ties. When placing the supplemental bars outside the original cage, it is necessary to increase the dimensions of the column to ensure sufficient cover. Hairpin ties made of stainless steel are commonly used to provide lateral support to the supplemental bars.
Concrete Removal
When it comes to removing concrete from a column cage, it is crucial to ensure that the column is unloaded beforehand. Failure to do so could result in severe consequences such as the buckling of longitudinal bars and potential compression failure of the column.
This is because the presence of load-bearing forces can put significant stress on the longitudinal bars, leading them to buckle under the pressure. This, in turn, can cause the entire column to fail under compression. Therefore, it is essential to take the necessary precautions and ensure that the column is unloaded before attempting to remove any concrete from the cage.
By following these guidelines, one can minimize the risk of structural failure and ensure that the column remains stable and secure. It is important to note that the safety of the structure should always be the top priority in any construction or maintenance project. Thus, taking the necessary precautions can go a long way in ensuring the longevity and stability of the structure in question.
Corroded Reinforcing Steel
When reinforcing bars suffer from corrosion and their cross-sectional area is reduced, it is not always necessary to remove them completely. Instead, additional reinforcing bars can be added to make up for the lost area. However, it is important to provide a lap length for the splice that corresponds to the amount of area that was lost due to corrosion on both sides of the supplemented corroded portion of the bar.
Any partially corroded reinforcing bars that are not removed must be cleaned thoroughly by sandblasting until they are stripped down to bare metal. This process will ensure that the bars are free from any remaining corrosion and will be able to provide the necessary structural support.
In cases where the corrosion is too severe and the bars have lost too much of their cross-sectional area, they must be replaced entirely with fresh reinforcement. The new bars that are added must have full laps on both sides to ensure that they provide adequate support and are securely anchored to the surrounding concrete.
Corroded Ties
When dealing with corroded ties, a possible solution is to replace them with stainless steel hairpin ties that can be anchored into the concrete. However, it is important to ensure that adequate cover is provided over the supplemental ties around columns. This may require depositing extra material in the affected areas. By taking these steps, the integrity and stability of the structure can be maintained or improved.
Low-strength Concrete
In situations where the strength of concrete is low and unable to carry sufficient loads, there are several alternatives that can be considered. One option is to shore the column and remove the existing concrete, replacing it with new concrete. Another alternative is to shore the column and increase the size of the column to reduce bending stresses and provide additional confinement to the weak concrete that has already been placed.
A third option is to wrap the column with carbon- or glass-reinforced plastic. This can provide additional strength and support to the column without requiring major structural changes. Finally, an additional column can be installed to supplement the existing structure and provide additional load-carrying capacity.
Each of these alternatives has its own advantages and disadvantages, and the choice will depend on the specific situation and the goals of the project. It is important to carefully evaluate each option and consider factors such as cost, feasibility, and long-term durability when making a decision.