Reinforcement of concrete shear wall

Shear walls are an important component of any structure that is subjected to variable shear forces and variable bending moments. These forces are at their maximum value at the base price of the wall. In addition, the compressive axial forces resulting from the weight of the upper floors falling on the shear wall are other important forces that enter the concrete, steel or brick shear wall.

In order to deal with lateral forces on a structure, which are usually caused by wind, storms or earthquakes, different solutions are proposed. All of these solutions aim to reduce damage caused by natural disasters or changes in the use of the building. In general, shear walls are much more economical than bending frames and protect the building from lateral forces by controlling displacements in the structures.

Shear walls can generally be classified into four categories: steel, masonry materials (brick), composite concrete and reinforced concrete or reinforced cement, of which we will examine the type of concrete.

Concrete shear wall
Reinforced cement or reinforced concrete shear walls are the most common types of shear walls that provide a reliable solution to deal with lateral forces caused by strong winds or earthquakes. These types of walls increase the building’s ability to resist seismic forces and their use in high-rise concrete structures is essential.

Today, reinforced concrete shear walls are widely used in small and large construction projects. In terms of implementation, these walls are executed horizontally and vertically. The thickness of this type of wall can vary depending on thermal insulation, number of floors, age of the building and other things. Typically, the thickness of concrete shear wall ranges between 14 and 50 cm.

There are two types of reinforced concrete shear walls: in-situ and prefabricated walls. The in-situ concrete shear wall is bonded to the perimeter frame to maintain consistency and continuity of the bars within the wall. This continuity is very important and affects the ability of the structure against lateral forces. The second type is prefabricated shear wall, which has a great influence on the appearance of the wall, the stability and malleability of the structure.

Reinforcement of concrete shear wall
The shear wall in the direction of the strong axis of the section is able to withstand the incoming lateral forces and transfer them to the foundation of the building. Shear walls are generally made individually with rectangular section or U, T and I shapes. An important advantage offered by concrete shear wall as a lateral load system is the high lateral rigidity that limits the lateral displacement of the building due to strong forces.

The adequate reaction against lateral forces, great rigidity and simple implementation process of concrete shear wall has made this structural system used today as one of the most popular lateral load-bearing members in small and large construction projects.

There are various ways to strengthen concrete shear walls, including the use of FRP fibers, steel plates, and concrete coating. Below, we will describe which of these three methods are among the most popular at the moment.

Reinforcement of concrete shear wall with concrete coating

One common method used to strengthen concrete shear walls is the use of concrete coating. Concrete covers can be implemented in different ways depending on the type of project. Filling the openings with reinforced concrete, increasing the thickness of the shear wall using concrete spraying and building a new shear wall next to the previous one are among the forms carried out in strengthening concrete shear walls with concrete coating.

To implement this method, in order to connect old and new concrete, screw implantation technology is used. Also, new implants are implanted inside the diaphragm and column

Reinforcing the concrete shear wall with steel plates

Anchor bolts are used to attach steel plates to concrete walls. This communication can be one-way or two-way. This method increases the strength and workability of the walls, but calculations must be made in such a way that brittle shear fracture does not occur in the concrete wall and the fracture is bending and soft.

Reinforcement of concrete shear wall with FRP fibers

One advanced and effective method used to reinforce and reinforce concrete walls or concrete shear walls is the use of FRP fibres. This technology increases bending and shear strength and prevents stress from being concentrated at a specific point. In this way, the structural wall shows much higher resistance to dynamic lateral loads generated by the earthquake. Also, in environments with unfavorable conditions, the walls are protected from the risks of corrosion and peeling.

Today, these fibers are used in structural reinforcement of reinforced or unreinforced concrete walls. Concrete shear walls, unreinforced concrete walls and masonry (brick) walls are types of structural walls that are strengthened in this way.

Strengthening the shear resistance of the concrete wall

FRP coating with concrete and reinforcement can greatly increase the shear strength of the wall. For this purpose, FRP sheets are installed in the longitudinal direction of the wall and parallel to the transverse stiffeners on both sides of the wall. If a shear crack is generated in the concrete wall due to incoming forces, the stress of the FRP coating increases and absorbs the forces. In this way, the yield strength, ductility and ultimate strength of the structural wall are greatly increased.

Flexural strengthening of concrete wall

To increase the bending strength of the concrete wall, the FRP cover is installed parallel to the height of the wall and parallel to the longitudinal stiffeners. In this case, the cover is installed vertically on both sides of the wall, and its end should be tied at the foot of the wall. Otherwise, the forces inside the FRP panels will not be transferred well to the foot support of the wall

Generally, a steel angle section is used to restrain the end part of FRP panels. For this purpose, they screw a steel corner to the wall support. Another way is that at the end of the layer, the sheared FRP panel is placed vertically on the curved FRP panel. Flexural strengthening of concrete wall with FRP panels results in greater cracking resistance, yield strength, secondary yield stiffness and ultimately increased ultimate strength.

Increase the ductility of concrete shear wall

Shear walls reinforced with FRP coating may have limited ductility, making them vulnerable to lateral forces caused by earthquakes. One of the most important reasons that causes this problem is the lack of a patch of longitudinal reinforcement in the parts where a plastic joint can be created.

Inadequate confinement in boundary sections and also lack of restraint of transverse reinforcements are other reasons leading to low ductility of concrete shear walls. Wall failure in such conditions is sudden and brittle and significantly reduces the bearing capacity of structures.

Internally enclosing concrete walls is one method commonly used to increase the effectiveness of the FRP coating. For this purpose, the walls should be divided into several sections by laying continuous reinforcement and reinforced steel, and then closed internally and externally with bolts or FRP fibers, respectively.