Table of Contents
Introduction:
Repair and Rehabilitation is the process of improving an existing structure for new conditions of use. It aims at restoring the structure to its original service level it once had and has now lost. In some cases, this consists of giving the structure the service level which was intended, but could not be attained because of deficiencies in the original design and or construction.
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Necessity:
Here are the main reasons why we need rehabilitation of structures.
- To Improve Surface Appearance
- To Improve Durability
- To Change In Live Load Pattern During Service
- Need For Enhancing Load Capacity
- After Failure of a Structure
There may be other reasons for the rehabilitation of structure as per requirement. In the figure below, we can see the difference in the appearance of the structure, before and after rehabilitation.
Causes of Failure of Structure:
A structure may fail due to many reasons. Some of them are –
External Causes:
It is one of the most important causes of the failure of a structure. It includes the failures occurred by the Accidents, Earthquakes, Floods, Fire, Foundation Settlement etc.
During the terrorist attack in 2001, the World Trade Centre in New York City was crushed. Therefore, rehabilitation may be needed to make it workable again.
Again, massive destruction occurs during Nepal earthquake in 2015, many important structures like monuments, buildings, towers etc. collapse down. Therefore, it is necessary to repair and rehabilitate those structures, if possible.
Ageing, weathering, deteriorating of Structure:
After construction of any structure, it is subjected to deterioration. With the increase of age, all the structural components are subjected to weathering. Therefore, it may fail after a few years.
Underestimating Loads:
Sometimes, the upcoming loads on a structure is much more than the design load, especially for the public building. Thus, the structure may fail due to overloading.
Lack of Maintenance:
After the construction of the project, it is necessary to maintain the structural component to its service level. This maintenance works may include repairing old and defective plaster, white-washing and colouring etc.
Wrong Design, Detailing and Construction:
During the planning and designing the project, it is possible that the designer did some mistakes and miscalculation, which may lead to failure of the structure. If all the design and detailing is perfect, it is also possible that the labours did mistakes during construction.
Wrong Connections in steel structure:
In the case of steel structure, if sufficient numbers of bolts or rivets are not provided, the structure may fail.
Overlooking the Other Factors:
A failure may occur due to more than one factors. Sometimes, we do not take care of other factors. Thus a structure may fail.
Not Consulting an Engineer:
Before constructing any major project, the owner of the project should consult an engineer for structural analysis and safety. Otherwise, there will be a risk of structural failure.
Types of Rehabilitation:
We can classify the works of repair and rehabilitation mainly in four types. They are –
- Constructional and Technical
- Architectural
- Public Facilities
- Social Life
These are discussed in short below-
Constructional and Technical:
Construction and technical equipment that refers to improving energy consumption and reducing the operating costs and maintenance ones.
Architectural:
Functional and aesthetic improvements so that the final result is the increase in the quality and appearance of the housing.
Public Facilities:
Improving facilities, equipment, housing and complementary facilities and increasing the availability of housing facilities and improvement of their qualities.
Social Life:
Improving the conditions of social and community life, conflicts reduction and improvement of the decision making by the community.
Materials Used for Rehabilitation:
Following are the materials which are commonly used for repair and rehabilitation of structure –
Un-modified Portland Cement Mortar or Grout- Latex Modified Portland Cement Mortar or Concrete
- Quick Setting non-shrink Mortar
- Polymer Concrete
- Epoxy Mortar or Concrete
- Methyl Methacrylate Concrete
And many more products are available in the market that can be used for rehabilitation.
Process of rehabilitation:
First, we need to investigate the causes & identify the problems and understand.
Then, we should use NDT methods to understand damages and defects.
Next step is to consider structural and operational requirements to select the rehabilitation method.
Finally, we have to select the right Repair Materials with appropriate methodology.
Methods of Rehabilitation:
Jacketing:
Jacketing is done for deteriorated columns, piles, Beams, Slabs etc.
Shotcreting or Guniting:
A concrete mix of very high workability is fired with compressed air. It is most suitable where water should not penetrate through the wall, like water tanks.
Stitching by Iron or Steel Dogs on Sides:
Stitching is done for cracks in beams or slabs.
External prestressing by Wires or Rods:
Sometimes, external wires, fibres or steel rods are embedded in the concrete. Experiments show that prestressing those wires increase the stresses to a higher limit.
Overlays on Defected Structure:
If cracks appear on flooring, it can be repaired by providing overlays. A thin layer of protecting material is provided above the old flooring to improve the appearance.
Other methods of repair and rehabilitation of structures are prepacked Concrete, Bonding with Injection of Epoxies under Pressure, Routing & Sealing, Grouting etc.
Final Thought:
It is evident from the above discussion that whenever a structure is constructed, it is subjected to deterioration. Hence, it is important to recognize the problems lies in the structure and give an appropriate treatment that would give long-term durability to the structure. Otherwise, it will lose its capability gradually.
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