Retrofit Techniques used for RCC structure

Retrofit Techniques used for RCC structure

Damage to concrete buildings is a global issue right now. This is due to a number of factors, including earthquakes and other natural disasters, a general lack of knowledge of crucial design codes in construction, inadequate oversight, and so on. As a result of these issues, the built environment becomes weak.

Overloaded structures can experience significant deformations and corrosion, both of which require urgent treatment at the present time. Repair, retrofitting, or strengthening reinforced concrete structures is a common practice in today's construction industry to counteract these consequences.

Many other methods exist for repairing the harm that could result from any of these causes; the one that proves to be most effective in any given circumstance will be chosen. It is not uncommon for even recently constructed buildings to need fixing and reinforcing to get rid of flaws that resulted from design or construction flaws.

methods of retrofitting

JACKETING

Using this method, extra concrete is added to the existing web in order to expand the structure's size. The structure's strength and ductility could be improved with the addition of reinforcement. The additional reinforcement may include both vertical and horizontal bars, resulting in a reinforcement mesh, or diagonal bars.

The additional support needs to be attached to the foundation of the structure. In one method of anchoring, the reinforcement is placed in holes that have already been drilled into the base, and the holes are then grouted with epoxy. The fresh concrete is put into place once it has hardened to the proper consistency.

Compared the performance of two RC buildings, one with its web concrete in the plastic hinge area repaired by adding diagonal bars, and another with its web concrete repaired by making it thicker (jacketing) .

Although the initial stiffness of the rebuilt structures was reduced to roughly half that of the original structures, testing demonstrated a gain in strength and deformation capacity. In cases where the structure's foundation is not sufficiently robust, further foundational reinforcement may be required to accommodate the larger dead load and the larger predicted lateral load.

ADDING STEEL BRACING

Rehabilitation of presumably ductile moment-resisting frame constructions is the most common application of steel bracings. As long as the connections to the existing structure are carefully considered, they can offer the necessary strength, stiffness, and ductility. Strengthening RC shear walls against earthquakes is possible with the use of steel bracings.

For instance, if the steel bracing is anchored to the RC structure at tiny intervals to minimise the buckling length, the capacity of the bracing member can be increased without having to refit the moment resisting frames, which is primarily governed by buckling of the compressed bracing member.

Since diagonal forces in bracing members will have a vertical (compression/tension) component, it is best practise to include vertical steel strips at the structure ends to resist some of these forces with the concrete.

Concrete replacement is the quickest and cheapest way to restore the strength and ductility of an RC structure. The damaged concrete must be removed, the aggregate must be exposed, and the surface of the old concrete must be cleaned to remove any loose debris and produce a tight bond between the old concrete and the new.

 It may be necessary to straighten the reinforcing steel bars in the compression zone of crushed concrete if they have gotten somewhat buckled. The web's formwork is set up on one side of the building, while fresh concrete is poured in from the other. For the final touch, a high-strength epoxy grout can be utilised to create a strong bond with the preexisting concrete.

The fresh concrete must cure when the forms are taken down. Thus, if the building needs to be accessible during repairs, fixing the shear structure via concrete replacement is not an option. Sometimes, low-viscosity epoxy resins can be used to seal the primary flexural cracks in an RC structure, which greatly increases the structure's strength and ductility.

Polymer Material

Fiber-reinforced polymer (FRP) composite materials are gaining popularity as a possible material for retrofitting of existing buildings because to its high strength, low weight, ease of application, Figure 2 Retrofitted RC structure employing steel bracings at 1.0% drift and strong resistance to corrosion.

The use of pre-stressed fibres in fiber-reinforced plastic (FRP) laminates, sheets, or rods can increase the efficiency of a retrofit. When it is not possible to completely vacate a building during a refit, FRP composites can provide the necessary strength with minimal disruption to building operations, making this a faster and easier retrofit option.

Retrofitting using steel material

Most RC buildings' older parts were replaced with steel when they were renovated. The response characteristics of RC shear structures were improved by various retrofitting strategies using steel sections.

Steel retrofitting solutions include advantages such as less extra weight to the structure (in comparison to concrete jacketing) and less interruption to the building's tenants. Retrofitting with steel, however, presents challenges due to the material's susceptibility to corrosion, the necessity of scaffolding, and the difficulty of handling the heavy steel plates on site.

Using steel sections

Strength, stiffness, or ductility can all be improved by using this method, which involves attaching steel plates to the structure. Steel plates can be attached in either a vertical or horizontal orientation, depending on the intended outcome. investigated the possibility of using a rehabilitation plan for retrofitting steel-plate shear structures to enhance a specific feature (such stiffness, strength, or ductility) without influencing any other properties.

Figure depicts a number of different restoration strategies for the structures under study. They determined that external steel plates attached along the length of the structure's towards the edges can increase the stiffness without affecting the strength, provided that a space exists between the plates and the foundation or top slab, as the critical section will remain the same. Increase the strength of the structure without sacrificing its stiffness by connecting external, unbonded steel plates or bars using an interaction delay mechanism (IDM).

Only once a predetermined displacement threshold is met does the IDM activate the supplementary plates or bars. Corrosion and fire resistance for the steel are provided by enclosing the plates or bars in a ductile material and attaching them to the slabs at the intermediate levels of the structure.

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