How are columns strengthened using encasement?

Short Answer:

Encasement is a method used to strengthen RCC columns by enclosing them with an additional layer of concrete, steel, or other strengthening materials. This technique increases the size and strength of the column, making it capable of carrying more load and resisting damage from external forces.

Encasement is used when a column becomes weak due to aging, corrosion, poor construction, or increased loading requirements. It helps restore stability, improve durability, and enhance the overall performance of the structure without removing the original column.

Detailed Explanation:

Columns strengthened using encasement

Encasement is a structural strengthening technique used in civil engineering to improve the load-bearing capacity and performance of existing RCC columns. It involves covering the column with an additional protective and reinforcing material, most commonly concrete or steel. The goal of encasement is to make the column stronger, more durable, and capable of resisting higher loads, seismic forces, or damage caused by environmental exposure.

Over time, columns in buildings or bridges may lose their strength due to corrosion of reinforcement, cracks, or increased load demands. Instead of replacing the entire column, which is costly and time-consuming, encasement provides a practical and efficient solution.

How Encasement Strengthens Columns

  1. Concrete Encasement:
    • A new layer of reinforced concrete is added around the existing column.
    • This layer increases the cross-sectional area, which improves the column’s strength and stiffness.
    • Additional reinforcement bars are placed and tied with the existing column before pouring the concrete.
    • Bonding agents or roughening of the old surface ensures good adhesion between old and new concrete.
  2. Steel Encasement:
    • Steel sections or plates are wrapped or bolted around the column.
    • The steel cover may be filled with grout or concrete to form a strong composite structure.
    • This method offers quick installation and is suitable for structures requiring fast repair or seismic strengthening.
  3. FRP Encasement (Fiber-Reinforced Polymer):
    • FRP sheets are wrapped around the column to enhance confinement and strength.
    • It is lightweight, corrosion-resistant, and effective in increasing ductility and resisting seismic loads.
    • It does not change the size of the column significantly, which is useful in space-limited areas.

Benefits of Column Encasement

  • Increased Load Capacity:
    By adding more material and reinforcement, the column can support higher loads.
  • Improved Ductility and Seismic Resistance:
    The confined section behaves better during earthquakes and reduces the risk of brittle failure.
  • Corrosion Protection:
    Encasement provides a cover that protects the internal reinforcement from moisture, chemicals, and environmental damage.
  • Extended Service Life:
    It helps in restoring and preserving aging structures, extending their useful life without full reconstruction.
  • Cost-Effective and Practical:
    Compared to replacement, encasement is easier, faster, and more economical. It also causes minimal disruption to the structure’s use.

Steps in Encasement of Columns

  1. Assessment:
    Engineers inspect the column to identify damage and determine the need for strengthening.
  2. Surface Preparation:
    The column surface is cleaned, roughened, and made ready for bonding.
  3. Installation of Reinforcement:
    Additional steel bars or FRP wraps are fixed around the column as per the design.
  4. Formwork and Concreting (in case of concrete encasement):
    Shuttering is placed around the column, and concrete is poured to form the new jacket.
  5. Curing and Finishing:
    Proper curing is done to develop strength, and the surface is finished smoothly.

Encasement is widely used in retrofitting of buildings, bridges, parking structures, and old industrial facilities where safety and load demands have increased.

Conclusion:

Columns are strengthened using encasement by enclosing them with extra concrete, steel, or FRP layers. This method increases the strength, stability, and durability of RCC columns without removing the original structure. Encasement is a simple and effective solution for upgrading damaged or weak columns and is commonly used in retrofitting works for long-term performance improvement.