Compression Failure of Concrete Columns- Causes & Repairs

Compression failure of R.C.C. concrete occurs when the axial load acting on the column exceeds the load-carrying (compression load) capacity of the given column. 

This article is a quick guide to understanding the compression failure of concrete columns, their prevention, how to identify a compression failure of the column, and various repair methods. 

What is Compression Failure of Concrete Columns?

Compression failure of a concrete column occurs when the compressive stresses developed within is greater than the allowable stress of the column. When axially loaded, both steel and concrete within the column experience stress. As the load increases beyond the column's capacity, the steel and concrete reach their yield strength, leading to immediate failure without significant lateral deformation.

We know that there are generally three categories of columns, namely:

1. Long Column le/d > 12
2. Pedestal le/d < 3
3. Short Column le/d ≤ 12

Note: "le" is the effective length of the column and "d" is the least lateral dimension of the column. The ratio is called as slenderness ratio. 

Short columns or pedestals are more prone to compression failure among the three types due to their inherent stiffness. They fail due to material crushing rather than buckling. Here's why:

• Limited Lateral Deformation: Short columns have a lower height-to-width ratio, restricting their ability to deflect laterally under load. This limits their capacity to redistribute stresses and absorb energy.
• Increased Stress Concentration: The restricted deformation leads to higher stress concentrations at the column's ends, making them more susceptible to failure. 
• Reduced Buckling Resistance: While buckling is more common in slender columns, short columns can still experience localized buckling under high compressive loads, especially if there are imperfections or eccentricities in the load application.

Failure of Short and Long Columns

How to Prevent Compression Failure of Columns?

1. Avoid overloading: Ensure the load remains within design limits.
2. Provide adequate cross-sectional area: The column's size should be sufficient for the applied load.
3. Provide adequate reinforcement
4. Limit compressive stresses: The developed stresses must be lower than the design strength

How to Repair Compression Failure in Concrete Columns?

During compression failure, the material starts to fail (concrete first) itself in the form of structural cracks, before complete column failure. Hence, structural cracks are an indication of excessive loading on the column.  

Read On : 4 Types of Cracks in R.C.C Columns

For example, the formation of diagonal cracks or splitting cracks is a few structural cracks that give us an indication regarding compression failure or crushing expected to occur in the column. This gives us time to retrofit the structure before complete collapse.

An extreme case of compression failure, known as concrete crushing, results in complete collapse and cannot be repaired. In such instances, the damaged column must be safely removed and replaced.

Unless this extreme condition happens, let’s look into various methods used to repair concrete columns with compression failure issues.

Concrete Column Repair Methods

1. Jacketing
• Steel Jacketing: A steel shell is installed around the column to provide additional strength and confinement.
• Concrete Jacketing: A concrete jacket, often reinforced with steel rebars, is applied to increase the column's load-bearing capacity.

  

  Concrete and Steel Jacketing of Concrete Columns

  
  
2. Fiber-reinforced polymer (FRP) Wrapping: FRP sheets are wrapped around the column to enhance its strength and stiffness. This non-invasive method is quick and efficient.

   

   Fiber-reinforced polymer (FRP) Wrapping of Concrete Columns

3. Injection Repair: Low-viscosity epoxy resin is injected into cracks to seal them and restore structural integrity.
4. Partial Demolition and Reconstruction: In severe cases, damaged sections are removed and replaced with new concrete and reinforcement. Note: Removal of concrete requires additional shoring to provide temporary support.

Key Considerations for Concrete Column Repair

To ensure a successful repair, the following factors must be carefully considered:

1. Structural Assessment: A thorough structural assessment is essential to determine the extent of damage and select the appropriate repair method.
2. Load Management
3. Load Reduction: Reducing the load on the damaged column can mitigate further deterioration.
4. Load Redistribution: Consider how load redistribution may affect the damaged column and adjacent structural members.
5. Material Selection and Application
• Material Compatibility: Repair materials should be compatible with the existing concrete and have adequate strength and durability.
• Workmanship: Proper construction practices and quality control are essential for the long-term performance of the repair.

Conclusion

Concrete columns are fundamental structural elements in buildings. When they experience compression failure, it can lead to severe consequences, including structural instability and potential collapse.

By understanding the mechanisms of compression failure, implementing preventive measures, and employing appropriate repair techniques, we can ensure the long-term safety and durability of concrete structures. Regular inspections, maintenance, and adherence to building codes are crucial in preventing and mitigating compression failure.