Retrofitting in the Construction Industry

Concrete is a very common material used in the construction of many buildings. It has been noticed that some of the buildings proved to be inadequate to resist lateral or vertical loads by current code requirements. This may be a result of poor design or damaged elements of buildings. Some of the elements may deteriorate during the life span of the building. One way of strengthening buildings to resist lateral loads is the introduction of shear walls but in this article, we’re going to talk about something different. That is, Retrofitting.

What is retrofitting?

The word retrofit means to apply new technologies to an older system. Retrofitting is a process of adding some new features that were not there before. Retrofitting in the construction industry refers to re-strengthening existing structures to make them seismic-resistant. It is an economic approach to increase the life span of an existing structure rather than redeveloping it.

Need of Retrofitting

There are several problems that structural members experience and need 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

WAYS to RETROFIT REINFORCED CONCRETE STRUCTURES

Concrete jacketing

Concrete jacketing is one of the very common techniques of retrofitting that is used to increase the structural integrity of beams, columns, and other structural elements. Reinforced concrete jacketing can be employed as a repair or strengthening scheme. Existing members that have been damaged should be repaired before they are jacketed. Jacketing of columns serves two purposes: (I) increasing column shear capacity in order to achieve a strong column–weak beam design, and (II) improving column flexural strength by extending the jacket longitudinally through the slab system and
anchoring it to the foundation.

To enhance the load-bearing capacity, flexural strength, and resistance to the shear forces of these structures, an extra layer of concrete is cast around the existing member. Extra longitudinal bars and stirrups are added within the new concrete layer to increase the flexural and shear capacity of the structure effectively. These reinforcements, coupled with the new concrete encasing, bolster the structural integrity of the original element, aiding in the restoration of structural design integrity following failures or revisions in the initial design.

Mostly after seismic events, this technique is employed in retrofitting structural elements that require additional support.

Steel Jacketing

Unlike CFRP jacketing where a Fiber Reinforced Polymer is used to wrap around the four corners of the column, steel section (usually angle steel) is used when it comes to steel jacketing. As the term jacketing implies, this method protects the column or member from being attacked by harsh weather conditions. Steel jacketing not only provides enough confinement but also prevents shell concrete deterioration, which is the primary cause of bond failure and longitudinal bar buckling. Encasing the portion with steel plates and filling the gap with non-shrink grout is referred to as steel jacketing. It is a very effective approach for correcting shortcomings
such as inadequate shear strength and longitudinal bar splices at critical locations. The member is encased by the steel sections and filled with grout which serves as a form of insulator for the member and corrosion protection. This technique is capable of greatly increasing the bearing capacity of the element thereby making it able to carry more loads. Steel jacketing appears to be useful in retrofitting columns because it helps restore column strength, ductility, and energy absorption capacity. In addition, the steel
jacket helps strengthen the lap-spliced column’s flexural strength and ductile behaviour, hence improving lateral performance. In the specification where the size of the element doesn’t significantly increase but high bearing capacity is required, steel jacketing is used.

This method is done by pasting the steel on the structural element through structural pouring glue or welding together the steel sections, and the newly added steel forms as one with the original component.

Steel Caging

This is a type of steel jacketing that involves reinforcing existing concrete elements by adding steel cages or frames around them. This procedure involves placing steel bars, plates, or mesh in a specific pattern around the concrete element to improve its durability, strength, and load-bearing capacity.

The steel cages are often designed to distribute forces evenly throughout the structure, providing additional support and preventing it from falling under stress or cracking.

Glass Fibre Reinforced Polymer (GFRP) Wrapping

In recent years, composite materials, such as Glass Fibre Reinforced Polymer (GFRP), have been used to strengthen and retrofit concrete structures. GFRP is designed to withstand tensile, compressive, bending, and shear forces, as well as secondary loading factors like creep, heat response, and moisture transport. Glass fibre-reinforced concrete is made up of high-strength glass fibres embedded in a concrete matrix, providing a combination of qualities that neither component could achieve on its own. The fibres act as load-carrying members, while the matrix transfers the load and protects the fibres from environmental degradation. Both continuous and discontinuous lengths of glass fibres can be integrated into the matrix.

Carbon Fibre Reinforced Polymer (CFRP) Wrapping

This is an excellent way to reinforce an RCC beam or column. This is mostly attained by wrapping the targeted structural element with Carbon Fiber Reinforced Polymer (CFRP) to strengthen the column or beam. In seismic-prone areas, structural elements are strengthened with the use of these FRPs. Research makes it known that the shear failure of the beam-column joint is the main reason for building collapse. One advantage of using this technique is that it is a lightweight material and doesn’t significantly increase the load on the structural element.

FRP material retrofitting is a technically sound and economical repair technology that is currently widely employed as a seismic retrofitting approach. The methods being referred (GFRP and CFRP) to are known for their quick and easy installation, resistance to corrosion, minimal impact on the structure’s appearance and geometry, minimal disturbance to occupants, high durability, high strength-to-weight ratio, improved work safety, reduced risk of hazards, and enhancement of both strength and ductility.

Other types of retrofitting includes the External Plate Bonding Method.

Benefits of Retrofitting

This method is more economical since the long-term savings in energy and maintenance costs often outweigh the upfront investment
It impacts the environment positively by decreasing energy consumption which translates to reduced greenhouse gas emissions and a more sustainable approach to building operations.
Retrofitting may be necessary to meet evolving building codes and regulations.
Retrofitting allows buildings to adapt to changing needs. For instance, the changes in environmental conditions.
Retrofitting can enhance a building’s resilience to natural disasters, such as earthquakes or hurricanes, and improve overall safety
It can help upgrade critical building systems and components leading to an extension in the overall lifespan of a structure. This is especially crucial for older buildings that may be more susceptible to wear and tear.
Retrofitting can also enhance the market value of a building.

Reference

Akshay, V.S., Prakash S.P., & Mayur A.B. (2014). RETROFITTING TECHNIQUES FOR REINFORCED CONCRETE STRUCTURAL MEMBERS USING DIFFERENT MATERIALS – A REVIEW. Journal of Emerging Technologies and Innovative Research. Retrieved from https://www.jetir.org/papers/JETIR2202146.pdf