Improving the seismic performance of concrete columns revolves around four core objectives: enhancing load-carrying capacity, improving ductility, optimizing force transfer mechanisms, and reducing seismic action. Appropriate methods should be selected based on the structural condition and retrofitting requirements. Below are mainstream and mature technical approaches, covering both direct retrofitting and indirect protection strategies:

Core Confinement Retrofitting (Enhancing Ductility and Shear Capacity, Most Commonly Used)

By confining the core concrete of columns with external materials, this approach delays cracking, prevents longitudinal reinforcement buckling, and avoids brittle failure during earthquakes, serving as the fundamental strategy for seismic retrofitting.

Reinforced Concrete (RC) Jacketing

Procedure: Bind new longitudinal and transverse reinforcement around the existing column, then cast a new layer of concrete to form an "outer jacket" that works synergistically with the original column.

Advantages: Simultaneously improves flexural capacity, shear strength, and ductility; exhibits excellent compatibility with the original structure; and has a wide range of applications.

Applicable Scenarios: Columns in old buildings with low concrete strength, insufficient reinforcement, or requiring significant performance upgrading.

Steel Jacketing Systems

Steel Plate Jacketing: Prefabricated steel plates are wrapped around the column via welding or bolted connections. Grout may be filled between the plates and the column to enhance bonding. It features fast construction, minimal increase in self-weight, and is suitable for columns with regular cross-sections and space-sensitive scenarios.

Angle Steel with Lacing Bars: Angle steels are installed at the four corners of the column, and transverse lacing bars connect the angles to form a steel skeleton, which is then integrated with the original column. It strengthens column corner protection and is applicable to rectangular columns with insufficient longitudinal or transverse reinforcement.

FRP Wrapping

Procedure: Carbon Fiber Reinforced Polymer (CFRP) or Glass Fiber Reinforced Polymer (GFRP) sheets/strips are wrapped around the prepared column surface using resin adhesives to provide circumferential confinement.

Advantages: Extremely lightweight, corrosion-resistant (suitable for coastal/chemical environments), adaptable to complex cross-sections, and exhibits significant confinement effects on core concrete.

Note: FRP materials are relatively brittle and should avoid direct impact loads.

Enhancement of Member Integrity (Optimizing Force Transfer and Addressing Weak Points)

By strengthening the connection between columns and other members or supplementing their own reinforcement, this method ensures effective force transmission during earthquakes and reduces local damage.

Beam-Column Joint Strengthening

Joints act as "force transfer hubs" during earthquakes, and joint failure directly leads to column ineffectiveness, thus requiring complementary retrofitting:

The joint region is confined with RC jacketing, steel jacketing, or FRP wrapping to enhance shear strength;

If joint reinforcement is insufficient, additional horizontal stirrups or longitudinal reinforcement are installed via post-installed rebar techniques to improve confinement.

Applicable Scenarios: All seismic retrofitting projects, especially for old buildings with missing joint stirrups or low concrete strength.

Post-Installed Rebar and Reinforcement Supplement

Targeted remediation of insufficient reinforcement in original columns:

Supplementing Longitudinal Reinforcement: Grooves are cut on the column surface, new longitudinal rebars are post-installed and anchored into the foundation and beams, then covered with concrete or grout;

Stirrup Densification: Additional circumferential stirrups are installed via post-installed rebar or drilled bar penetration to strengthen the confinement of core concrete.

Advantages: Directly addresses the issue of "insufficient reinforcement" and exhibits good integration with the original structure.

Indirect Seismic Mitigation Methods (Reducing Seismic Action at the Source)

Instead of directly enhancing the columns themselves, these methods reduce the seismic input energy by adjusting the dynamic characteristics of the structure, thereby indirectly protecting the columns.

Base Isolation

Procedure: Isolation devices (e.g., rubber isolation bearings, sliding isolation bearings) are installed between the structure's foundation and superstructure to form a "flexible buffer layer".

Advantages: Significantly reduces the seismic shear force and acceleration borne by the superstructure (including columns), making it the most efficient "source control" measure for seismic resistance.

Applicable Scenarios: Buildings with high seismic requirements (hospitals, museums), requiring integration with the overall structural design.

Energy Dissipation

Procedure: Energy dissipators (friction-type, viscous damping-type, metal yielding-type, etc.) are installed at beam-column joints or between columns and braces.

Advantages: During earthquakes, energy dissipators consume seismic energy through deformation, reducing the force and damage to column bodies. Damaged dissipators can be replaced post-earthquake to restore structural functionality.

Applicable Scenarios: Retrofitting of existing buildings, especially when major modifications to the main structure are impractical.

Targeted Repair and Load Sharing (Adapting to Damage or Special Needs)

Concrete Replacement

When column concrete suffers severe deterioration (carbonation, freeze-thaw damage, spalling), the deteriorated portions are first removed, then new concrete with high strength and ductility (fiber-reinforced if necessary) is cast to restore and enhance performance.

Adding Braces/Shear Walls

New steel braces, concrete braces, or shear walls are added to the structure to actively share the horizontal seismic forces borne by columns, indirectly reducing the load on columns and improving the overall structural stability.