Retrofitting of concrete wall | types of retrofitting | techniques

 Retrofitting for strengthening concrete wall

Existing reinforced concrete walls must be strengthened when they lose their strength and capacity to handle the specified loads, or when their load carrying capacity must be increased. This type of rehabilitation is typically necessary for walls built in high-seismic-hazard zones.

For the reinforcement of concrete walls, many retrofitting techniques can be used, utilising either classic or new materials.

Concrete Wall Strengthening Techniques

The following are some of the strategies for strengthening:

1.       Concrete Jacketing

2.       Concrete Replacement

3.       Retrofitting by Steel Materials

4.       Shape Memory Alloys

5.       FRP Laminates

 

1.     Concrete Jacketing

This is a classic retrofitting approach in which the retrofitting technique is used to enhance the wall's dimension. The new concrete is added to the existing concrete wall to give it more dimension. Additional steel reinforcement is added to the R.C wall to boost its strength and ductility.

The new steel reinforcement is formed into a mesh of horizontal and vertical bars that is then anchored to the foundation of the wall. The reinforcing mesh can also be put into a drilled hole in the foundation, then grouted and sealed with epoxy.

Jacketing is a structural strengthening and retrofitting technique. It's utilised to boost bearing load capacity after a structural design change or to restore structural design integrity after a structural member failure. Vertical surfaces such as walls, columns, and various combinations such as beam sides and bottoms are all used with this technique. Around the existing column, it comprises of additional concrete with longitudinal and transverse reinforcement. Jacketing is the process of restoring or increasing the size of a piece of an existing structural element by encasing it in appropriate materials. Around the damaged portion, a steel reinforcement cage or composite material wrap can be built, then shotcrete or cast-in-place concrete can be applied.

Jacketing is commonly used to repair corroded columns, piers, and piles, and it can also be used in underwater applications. The procedure can be used to prevent concrete, steel, and wood components from further deterioration as well as to strengthen them. Jacketing improves the axial and shear strength of columns, avoiding the need for extensive foundation reinforcement.

Because the approach concentrates on increasing the thickness of the wall, going beyond a certain point increases the dead weight. In order to support the added weight, the present foundation's load capacity would need to be increased.

When is it necessary to do jacketing?

Jacketing is the technique of reinforcing weak RCC members that have deteriorated over time as a result of unfavourable weather conditions or poor construction maintenance. Other issues that arise during the construction phase include design flaws, poor concrete manufacturing, and a sloppy execution process. During the service life of the structure, the need may arise as a result of an earthquake; an event, such as collisions, fires, or explosions; situations requiring changes in structure functionality; or the creation of more stringent code requirements.

·         The wall's load capacity is increased.

·         When a design flaw is discovered.

·         Weathering activity has caused the wall to deteriorate.

·         Walls are deteriorating.

·         Other factors, such as earthquakes and fires, have caused significant damage.

Jacketing's Benefits

·         It improves the earthquake resistance of member.

·         Because foundation strengthening is not necessary, the amount of work is reduced.

·         It improves the member's shear strength.

·         It also tightens the concrete confinement in circular columns.

·         It does not add to the column's major weight and also saves time during construction (curing).

 

Various types of jacketing

Reinforced concrete jacketing

The task of reinforcing reinforced concrete members should be performed by a structural engineer based on calculations. Only a few options are presented here to show how the strengthening could be accomplished. Jacketing and installing an extra cage of longitudinal and lateral tie reinforcement around the columns, as well as casting a concrete ring, are the best ways to strengthen RC columns. The above method can also be used to jacket a reinforced concrete beam. In this situation, holes will have to be drilled into the slab to hold the stirrup.

Steel jacketing

Steel jacketing is another good way to boost basic strength. Steel jacketing not only offers sufficient confinement, but it also inhibits shell concrete deterioration, which is the primary cause of longitudinal bar bond failure and buckling. Encasing the portion with steel plates and filling the gap with non-shrink grout is known as steel jacketing. It's a great way to fix flaws like poor shear strength and splices on longitudinal bars at important points. However, it may be expensive, and fire resistance must be considered. Steel strips and angles are the most popular method of reinforcement in practise. Steel jacketing aids in the restoration of a column's strength, ductility, and energy absorption capacity.

Steel strips and angles are the most widely employed strengthening technique in practise. Steel jacketing appears to be useful in retrofitting columns because it helps to restore column strength, ductility, and energy absorption capacity. Furthermore, the steel jacket aids in boosting the flexural strength and ductile behaviour of lap-spliced columns, hence improving lateral performance.

 

2.     Concrete Replacement

This is one of the most straightforward and cost-effective methods for restoring the strength and ductility of R.C walls. The procedure begins with the removal of the damaged concrete. To eliminate all loose materials, the finished surface is thoroughly cleaned and brushed. If minor sections of reinforcement in the compression zone have buckled, it should be straightened.

The formwork for the wall web is prepared when the preparation is completed. Fresh concrete is poured into the formwork from one side of the wall. The wall is cured after it has been concreted. Because great strength is required to bring touch with the existing concrete, the top half of the wall can be finished with epoxy grout.

 

3.     Retrofitting by steel material

The use of steel to retrofit R.C walls adds only a tiny amount of weight to the existing structure. It is a method of retrofitting that causes the least amount of inconvenience to the building's tenants.

A.      Steel Sections Retrofit: Steel plate sections are added to the R.C Wall surface to help increase the wall structure's strength, stiffness, and ductility. The steel plate piece can be inserted vertically or horizontally, depending on the property to be improved.

B.      Steel Bracing Retrofit: Steel bracings are commonly used for moment-resisting frame systems. The structure's strength, stiffness, and ductility are ensured by properly connecting the bracing to the existing walls.

Steel bracing also improves the R.C structure's seismic performance. Steel bracing placed at appropriate intervals on the R.C walls reduces buckling length, increasing the bracing member's capability.

 

4.     Retrofitting using shape memory alloys (SMA)

Shape memory alloys have gotten a lot of attention in civil infrastructure research, where they're considered as having a bright future in structure retrofitting. Various studies and researches are being conducted on the usage of SMA for the retrofitting of RC walls.

The SMA is capable of suffering significant deformations. The SMA structure regains its original shape when the force applied to it is removed. This means that SMA increases ductility and energy dissipation capacity without the member experiencing any permanent deformation.

5.     FRP Laminates

Retrofitting reinforced concrete walls using composite materials such as fibre reinforced polymer (FRP) in various forms has been a method utilised for decades. FRP has a strong strength and corrosion resistance. Furthermore, they are light in weight and may thus be applied quickly.

Over a R.C wall, FRP can be used as laminates, sheets, or rods. By prestressing the fibres, the efficiency of this retrofitting can be enhanced. FRP composites are a simple and quick method of retrofitting.