What Is Retrofitting?
Retrofitting is the method of modifying or repairing something after it has manufactured. Retrofitting work includes changing or repairing the structure system of a building after its construction and occupation. This work result in increased safety and durability of the structure.
Retrofitting of buildings is required for homes that are affected by failures and damage by seismic forces. Retrofitting done for your home makes it resistant to seismic activity caused by earthquakes.
Retrofitting of structures means making changes to an existing building to protect it from flooding or other hazards such as high winds and earthquakes.
Retrofiting of RCC structural members is carried out to regain the strength of deteriorated structural concrete elements. The strength deficiency of concrete structural members can be due to poor workmanship, design errors, and deterioration due to the aggression of harmful agents.
The main goal of retrofitting is to stabilize the current structure of buildings and making them earthquake resistant.
What Is Need Retrofitting
There are several problems that structural members experience and needed to be tackled among them some common problems include:
- Structural cracks
- Damage to structural members
- Excessive loading
- Errors in design or construction
- Modification of the structural system
- Seismic damage
- Corrosion due to penetration- honeycombs
Methods of Retrofitting of Building
The following are the most common methods in retrofitting of a building
- Adding New Shear Wall
- Adding Steel Bracing
- Wall Thickening Technique
- Base Isolation Technique
- Mass Reduction Technique
- Jacketing Method
- Fiber Reinforced Polymer (FRP)
- Epoxy Injection Method
- External Plate Bonding
1. Adding New Shear Wall:
- This is a frequently used technique for retrofitting of building of non-ductile reinforced concrete frame buildings.
- The elements can be either cast-in-place or pre-cast concrete elements.
- New elements preferably are placed at the exterior of the building.
- This method id not preferred in the interior of the structure to avoid interior moldings.
2. Adding Steel Bracing:
- Steel bracing is an effective solution in the retrofitting of building when large openings are required.
- Potential advantages due to higher strength and stiffness and opening for natural light can be provided.
- The amount of work is also less so foundation cost may be minimized and adds much less weight to the existing structure.
3. Wall Thickening Technique:
- The existing walls of a building are added a certain thickness by adding bricks, concrete, and steel aligned at certain places as reinforcement.
- The weight of the wall increases and it can bear more vertical and horizontal loads.
- Also, it is designed under special conditions that the transverse loads do not cause sudden failure of the wall.
- Rust can be developed on reinforcement if not covered properly by mortar.
4. Base Isolation Technique:
- Isolation of superstructure from the foundation is known as base isolation. It is the most powerful method for passive structural vibration control techniques.
- When building isolates from the ground it causes lesser seismic loads, hence lesser damage to the structure and minimum repair of the super-structure.
- The main demerit of this method is, it cannot be applied to structures like other retrofitting and expensive in the budget.
- This method is inefficient for high rise buildings and not suitable for buildings rested on soft soils.
5. Mass Reduction Technique:
- In mass reduction technique, for instance, by removal of one or more storey’s as shown in the figure.
- In this method, it is evident that the removal of the mass will lead to a decrease in the loading, which will lead to an increase in the required strength.
6. Jacketing Method:
- It is most used method of retrofitting o f building.
- Jacketing is the most popularly used method for the strengthening of columns and beams of a building.
- Jacketing consists of added concrete with longitudinal and transverse reinforcement around the existing columns.
- It improves the axial and shear strength of the column and major strengthening of the foundation may be avoided.
- The amount of work is less as foundation strengthening does not require and increases the shear strength of the column. It also increases the confinement of concrete in circular columns.
- Steel jacketing does not increase the significant weight of the column and also saves construction time.
7. Fiber Reinforced Polymer (FRP):
- A fiber-reinforced polymer is an axial strengthening system which used to improve or enhance the capacity of reinforced concrete beams.
- It can be used for both circular as well as a rectangular-shaped column but it is more effective in former shape.
- FRP increases the ultimate load-carrying capacity of reinforced concrete members and improves the shear capacity of the reinforced concrete element.
- Also, the ductility of a reinforced concrete column is increased considerably.
- Composite must be dried before repair because all resins and some fiber absorb moisture.
8. Epoxy Injection Method:
- Epoxy injection is an economical method of repairing of non-moving cracks in the concrete walls, slabs, columns, and piers. In retrofitting of building, epoxy injection is used to fill and repair the structural fault.
- It is capable of restoring the strength of concrete to its pre-cracked strength.
- The epoxy tensile bond to the concrete is stronger than the tensile strength of concrete.
- Strengthening is provided by installing additional reinforcement across the failure plane in combination with the epoxy resin injection.
9. External Plate Bonding:
- Strengthening of reinforced concrete beams with external plates or strips is a conventional method and has been utilized for many decades.
- The external plate bonding method can be used for increasing the shear strength of reinforced concrete beams by completely or partially wrapping steel plates at the joint of a column and beam.
- An external plate providing perpendicular to potential shear cracks is effective to increase the shear strength of the concrete reinforced member.
- The additional shear strength is achieved, but depending on beam geometry, existing concrete strength, and applied the wrapping method.
Read More: 8 Foundation Repair Techniques and Methods
10. Section-Enlarging Reinforcing Method:
- The enlarged cross-section method is used to increase the components of the reinforcement area, which enhance the bearing capacity and also increase its cross-section stiffness and change the natural frequency of vibration.
- This method is widely used in the reinforced concrete structure of the beam, slab, column, etc.
- The enlarged cross-section method is suitable for the reinforcement of reinforced concrete bending and compression member.
Factors Affecting in Selection of Retrofitting of Building Methods:
The following factors should be kept in mind while selecting a method of retrofitting for building:
- Existing concrete strength.
- Accessibility to work areas.
- The magnitude of strength to be enhanced.
- Cost of construction and maintenance.
- Time constraints.
- Clearance issues.
- Seismic effect consideration.
- Environmental aspect.
Identify the Structural Damages and Their Retrofitting Process
1. Retrofitting of Corroded Structural Member
If corrosion has started, the following process is adopted:
- Remove weak concrete and expose reinforcement all around.
- Clean the rust of steel by wire brushes or sandblasting.
- Apply rust removers and rust preventers.
- Reinforce to supplement rusted steel if required with anchorage i.e. shear connectors.
- Apply tack coat or bonding coat (to provide a bond between the old concrete and new concrete) of polymer and epoxy resin-based bonding material.
- Use one of the patching technique to restore concrete to the original surface level. Polymer defined mortars are very good. This can be used with or without guiniting.
- Injection of cement slurry or polymer-modified slurry or epoxy to fill up pores or internal cracks or honeycombing.
- Apply a suitable protecting coating.
2. Retrofitting of Severely Damaged Concrete:
In case when the original concrete is in very bad condition and the injection of grouting is not able to rehabilitate the section to take the required loading, RCC Jacketing of the concrete section is to be provided.
- Provide the essential supporting system to the structure.
- Remove weak concrete.
- Clean the surface and clean the corroded part of the steel.
- Apply rust removers and rust preventers.
- Provide additional steel all around the structure.
- Provide required formwork.
- Provide a polymer-based bonding coat between old and new concrete surfaces.
- Place the concrete of required thickness, grade, and workability admixed with different admixtures.
3. The benefit of Retrofitting of Building:
The followings are the benefits of the retrofitting of building technique:
- This technique is used to prevent displacement from the concrete foundation of the structure.
- It improves the stability and safety levels of the structure.
- Retrofitting buildings are more adaptable and suitable for existing activities or future activities and making a building more comfortable to resist loading.
- Helps to prevent damage to the structure and injury to the occupants.
- Retrofitted buildings are more energy-efficient and lower carbon emissions from the building operations.
- The process helps to improve a residence’s ability to keep residents safe when there is an earthquake.
- Retrofitting also helps to make homes more habitable after any major earthquake.
- Also, when you get retrofitting done in your home, most insurance companies have increased their insurance benefits.
- Increasing the local capacity of the structural and non-structural components.
4. Demerits of Retrofitting of Building
Other than the advantages, retrofitting also has several disadvantages, such as:
- The skill of the worker must be complying with the adopted retrofitting approaches
- Limited access to the construction site, since the building could be still in function.
- Difficult of bonding mat be arise between old masonry and the new concrete surface.
- Concrete has higher strength than old masonry structure, thus special care should be given to specify the strength of overlaid concrete.
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