If damage in a building following an earthquake is limited to specific components, and the overall structure retains adequate lateral rigidity and remains in good condition, it may be sufficient to simply repair the damaged elements.

Repairing and Strengthening Beams

There are various approaches to repairing and reinforcing beams:

One method involves increasing beam capacity by affixing carbon fibres or steel plates with high-strength adhesives. This is applied to the side faces of beams subjected to static loads, enhancing their shear strength. By applying it to the lower face of the beams, the bending strength within the span is improved. In this technique, steel plates are attached to the face of reinforced concrete elements using epoxy resin, and then clamped against the concrete surface until the resin hardens.

Another method is the sheathing technique, wherein a new reinforced concrete layer is added to one, two, three, or four faces of the beam. The primary advantage of this method is the ability to place stirrups on the mantle, as well as the potential for longitudinal reinforcement, increasing both shear strength and bending strength. When repairing and reinforcing beams using reinforced concrete, it is crucial to ensure proper adhesion of the reinforcement to the concrete, anchoring of the reinforcement, and bonding of the existing and new concrete.

Repairing and Strengthening Columns

Columns must be repaired and reinforced to boost the lateral load-bearing capacity of damaged columns or to ensure they can withstand the effects of an earthquake.

By adding reinforcements to the columns’ new dimensions and increasing the cross-sectional area, the bending strength of the columns is enhanced. Concurrently, compressing the transverse reinforcement provides ductility and shear strength.

For columns with minor cracks, the injection technique is typically employed for repair. Cement mortar or resin is injected into the areas opened at 20 cm to 100 cm intervals, depending on the crack width.

If local crushing is present in the columns, the damaged concrete in the affected area should be removed, the concrete surface cleaned, and the existing concrete in the damaged area saturated with water before pouring new concrete.

In cases where column strength is insufficient or damage is extensive, reinforcement and repair can be achieved using the sheathing technique with a steel jacket and reinforced concrete jacket. This method involves adding reinforcement and concrete sections to the existing column. The new column should be no less than 10 cm thick to ensure proper integration with the existing column. A sheathing that covers the entire perimeter should be used to guarantee full-force communication between the new and existing concrete.

Repairing and Strengthening Column and Beam Joints

The most severely damaged areas during an earthquake are often the junctions between columns and beams in a structure. At the same time, repairing and reinforcing these joints can be particularly challenging.

Repairing column and beam joints demands significant effort and attention due to the high number of connecting elements, intense stresses, and the difficulty in joining, anchoring, splicing, and maintaining the continuity of the reinforcing parts.

Inadequate joints, reinforcement clamping, and shear strength under earthquake conditions are common causes of damage.

The methods used to repair and strengthen columns and beams can also be employed for repairing and reinforcing joints.

For minor cracks, epoxy resins may suffice, restoring the adhesion between concrete and reinforcement to its original level. However, cement injection alone is insufficient to restore adhesion between concrete and reinforcement. If the reinforcement is damaged or the concrete crushed, the affected section must be removed and replaced.

Repairing and reinforcing joints of columns and beams involves sheathing both the beam and the column at the nodal point. The concrete cover is removed so that new reinforcements can be welded to the existing reinforcement. Transverse and horizontal and vertical reinforcement bars should be connected in a skeletal manner.

The integration of the connecting elements is achieved using the sheathing method. To ensure proper integration of the new and existing concrete, welding may be necessary to remove the cover layer and clamp the short reinforcements. Additionally, the stiffness of the jacket must be adequate. Level and horizontal stirrups in the region should also be placed at the nodal point to obtain sufficient shear strength.

Column and beam joints can also be repaired and strengthened by adhering and wrapping steel strips in cases where damage is localised and manifests as cracks.