Strengthening of existing reinforced concrete walls becomes necessary either when they lose their strength and capacity to take up the stipulated loads or when you need to increase their load carrying capacity. This kind of rehabilitation is mostly required for walls constructed in high seismic zone areas.
Different retrofitting techniques can be applied by using the traditional materials or new materials for the strengthening of concrete walls.
Methods to Strengthen Concrete Walls
The methods of strengthening include :
- Concrete Jacketing
- Concrete Replacement
- Retrofitting by Steel Materials
- Shape Memory Alloys
- FRP Laminates
1. Concrete Jacketing
This is a traditional retrofitting method, where the retrofitting technique is performed to increase the dimension of the wall. This increase in dimension is achieved by adding new concrete to the existing concrete wall. For this, additional steel reinforcement is placed to increase the strength and ductility of the R.C wall.
The new steel reinforcement is made into a mesh of horizontal and vertical bars, which is then anchored to the wall foundation. The reinforcement mesh can also be inserted into a hole drilled into the foundation after which it is grouted by epoxy and sealed.
As the method focuses on the increase in the wall thickness, an increase beyond a limit increases the dead weight. This would demand the increase in load capacity of the existing foundation in order to take the additional weight.
2. Concrete Replacement
This is one of the simplest and cheapest way to restore the strength and the ductility of the R.C walls. The method initially involves the removal of the damaged concrete. The final surface is cleaned and brushed properly to remove all loose materials. If the reinforcement present in the compression zone is buckled in small amounts, then it should be straightened.
After the preparation is done, the formwork for the wall web is prepared. Into the formwork, fresh concrete is poured from one side of the wall. After concreting, the wall is cured. The top part of the wall can be completed by an epoxy grout as high strength is required to bring contact with the old concrete.
3. Retrofitting by Steel Materials
The use of steel for retrofitting R.C walls only adds a small weight to the old structure. It is a retrofitting technique that causes minimum disruption to the building occupants.
1. Retrofitting by Steel Sections: Steel plate sections are added to the R.C Wall surface which helps in increasing the strength, stiffness and the ductility of the wall structure. Based on the property to be enhanced, the steel plate section can be added either vertically or horizontally.
2. Retrofitting by Steel Bracing: Use of steel bracings is common for moment resisting frame structures. Proper connections of the bracing with the existing walls ensure adequate strength, stiffness, and ductility for the structure.
Steel bracing also increases the seismic performance of the R.C structure. Providing steel bracing at proper intervals on the R.C walls decreases the buckling length that in turn increases the capacity of the bracing member.
4. Retrofitting using Shape Memory Alloys (SMA)
Shape memory alloys have been gaining a great amount of attention in civil infrastructure researches it is to have a huge future in retrofitting of structure. The use of SMA for the retrofitting of RC walls is being studied through various tests and researches.
The SMA has the property of undergoing large deformations. When the stress applied to the SMA structure is removed, it regains its original shape. This means SMA gains ductility and energy dissipation capacity without undergoing any form of permanent deformation in the member.
5. Use of FRP Laminates
Use of composite materials like Fibre reinforced polymer (FRP) in different forms for retrofitting reinforced concrete wall is a method used from past decades. FRP gains high strength and high resistance to corrosion. In addition to this, they are light in weight and therefore can be applied easily.
FRP can be used as laminates or sheets or as rods over the R.C wall. The efficiency of this retrofitting can be increased by prestressing the fibres. FRP composites is a fast and easy retrofitting technique.