Strengthening concrete structures

Many reinforced concrete structures may, for various reasons in design, production or even implementation, lose some of their strength against lateral forces or stresses that usually arise after a few years in the building or structure. In this article, we will explain the reasons for strengthening concrete structures and show you how this very important work is usually accomplished.

What are the advantages of concrete structure?

As you have seen in your daily routine, concrete structures are almost an integral part of small and large construction projects. Of course, this popularity is not without reason, and the advantages offered by concrete structures have led many employers to prefer the use of these structures over other methods. In the following, we will learn about the most important advantages of concrete skeleton.

High ductility and can be used in all small and large construction projects
Maintenance costs for concrete structures are lower than steel structures
Ease of implementing concrete structures and reducing the need for specialized personnel
Higher strength and durability in adverse environmental conditions
Ability to allocate funds step by step
Higher resistance to fire and high temperature
Less bending of components against applied forces
Faster execution time than steel types
Production and implementation costs are much lower
Weakening factors of concrete structures

Concrete structure or reinforced concrete is one of the most important components that is widely used today in the construction of residential or commercial buildings and large construction projects such as bridge building or dam construction. Concrete structures are by far one of the strongest components used in construction. In the production of this type of structure, a mixture of sand, cement, sand and steel or ribbed reinforcement is used.

However, corrosion of steel reinforcement, change in building use and adverse environmental conditions such as extreme cold may result in these structures needing to be strengthened or repaired. Low quality of concrete, inappropriate reinforcement, defects in concrete, poor quality of materials, and increased seismic and dynamic load in the concrete structure are all important reasons why concrete structures need to be strengthened.

If, after the above tests, the strength capacity of the load-bearing concrete structure differs by 15% or more from the figure calculated at the time of design, the structure needs to be strengthened or repaired. In these experiments, reliability coefficients are usually omitted to bring the results closer to reality

Concrete slabs and concrete buildings are strengthened by   Bikaran Sazan Shamal Company. For a free consultation and price inquiries, call 88797928-021

Strengthening the concrete structure and its causes

Fortunately, today there are many solutions for strengthening concrete structures that are used according to the building use, construction site and specific constraints. To determine the strength of a concrete structure or concrete structure, it must be tested. These tests are available in both destructive and non-destructive forms, and the data obtained from them are reliable.

Unfortunately, many buildings whose concrete structures are based on pre-1970 regulations have various weaknesses in strengthening and implementation. The presence of various defects such as low lateral displacement capacity, low energy dissipation, etc. in these concrete structures has caused them to be exposed to the risk of collapse and destruction in earthquake-prone areas.

If we want to present the major weaknesses of concrete structure as a list, perhaps the following can present the weaknesses of concrete structure well.

Shear failure of short members or side connections with short effective length
Delamination of main concrete core in earthquake-induced oblique cracks
Tighten the straits and move out of their original place
Oblique cracks form in the concrete core
The reinforcement comes out of the specified position
Making diagonal incisions in the shear wall
Bends in longitudinal reinforcement

Remove the concrete cover

Concrete is one of the building materials with relatively good compressive strength, which provides low tensile strength. If the concrete structure is not strengthened with rebar, by applying high loads, various and generally diagonal cracks will be created in the structure, and eventually this will lead to complete destruction of the structure. However, in reinforced concrete structures, tensile stiffeners are used.

One of the challenges in concrete structure strengthening projects is selecting the right materials to repair or strengthen the structures, making this a specialized process. As mentioned, different methods are currently used to strengthen concrete structures. Below, we will mention some common and widely used methods.

Strengthening the concrete structure by adding a shear wall

One of the most common methods used to strengthen concrete structures is the addition of infill shear walls. Installing RC filler significantly increases the lateral and rigid bearing capacity of the structure.

In order to implement this method, the existing dividing walls of the building are removed and high-strength reinforced concrete shear walls are installed in their place. These shear walls have high resistance to lateral earthquake loads and significantly limit building movement.

Reinforcement of the concrete structure with concrete and steel jacket

Reinforcing concrete structures using concrete jackets and steel jackets is one of the common methods used in construction projects. Before this method became popular, the concrete cover of the structure was cracked and additional rebar was placed in it. This gap is then completely filled with a very strong and special adhesive and resin.

The problem with this method was corrosion of the steel reinforcement, for which there was no solution. But today, steel sheets or plates are used to strengthen concrete structures, the so-called steel jackets. In this method, steel plates are glued to the outer structure of the members

In this method, the shear, flexural and compressive strength of the structure is increased and the ductility of the structure is also improved. Although this method has a low implementation cost, some limitations make it impossible to use this method in every project.

In the concrete envelope method, reinforced concrete coatings are used instead of existing materials and structures. In this method of strengthening a concrete structure, the amount of ductility and rigidity of the structural components is increased and ultimately the overall strength of the building is improved.

Unfortunately, while implementing this method, the building cannot be exploited and requires the evacuation of the building and the destruction of existing concrete structures on a large scale. Increased cross section and dead loads in the concrete structure are other disadvantages of this method.

The middle of concrete or stone slab frames

To increase the strength and rigidity of structures, the technology of adding reinforced concrete panels or masonry (brick walls) can be used. This is one of the most common methods of strengthening concrete structures. These walls are usually installed as concrete block or shotcrete walls.

In this method, it must be considered whether the concrete frame of the building can be considered part of the composite system or not. In simpler terms, to apply this method, the bearing capacity of the existing columns of the structure must be checked as boundary members and components of shear walls. If this capacity is not ideal, it is possible to construct shear walls completely separate from the existing concrete frame, with the necessary elements and boundary components.

Use curved frames

Bending frames have very good ductility and energy loss if produced and executed according to specified standards. Due to the low rigidity of these frames, their interaction with lateral forces (such as earthquakes) will have severe deformations and will naturally cause problems for some non-structural components. In addition, increased secondary deformation can lead to overall structural instability.

Bending frames are generally used to absorb the forces applied by these frames after the destruction of the rigid systems and to prevent complete collapse of the building. These frames can also be installed externally.

Reinforcing the concrete structure with FRP fibers

Sometimes we need materials to strengthen concrete structures as well as increase the capacity of the structure against adverse environmental conditions to increase the durability of concrete. FRP fiber reinforced polymers are one of the best new methods used to strengthen concrete structures. These fibers can now be used in various forms such as fibres, panels and reinforcements.

FRP is a composite material with very high tensile strength, which is made from a special type of resin. Low weight, very good resistance to corrosion and environmental conditions, have made this material widely used in strengthening buildings today.

Frequently asked questions about strengthening skeletal structures

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