PSI - Issue 52

Sairam Neridu et al. / Procedia Structural Integrity 52 (2024) 267–279 Sairam Neridu/ Structural Integrity Procedia 00 (2019) 000 – 000

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encasement is determined based on the FEM analysis, which takes into account the required strength, stiffness, and load distribution. The encasement should be of an appropriate thickness to provide the necessary strength and stiffness to the pier wall. This will ensure that the pier wall can withstand the existing loads and any future loads that may be imposed on it without experiencing excessive stress or deformation. Figure 6 will show the recommended restrengthening technique carried to the pier wall. 5.4. Site Execution The recommended restrengthening technique of encasing the pier wall with concrete should be executed with great care to ensure a proper bond with the existing pier wall and to avoid creating any additional stresses or deformations. The execution process should be closely monitored and carried out according to the step-by-step procedure shown in figures 7 to achieve the desired strength and stiffness of the pier wall. The six main steps involved in the execution process are surface preparation, crack preparation, grouting of cracks, placing of reinforcement, placing of new reinforcement, and curing and de-shuttering. Surface preparation involves cleaning the surface, chipping and cutting to the required depth, and cleaning the surface again. Crack preparation involves cutting a V-groove or U-groove for cracks exceeding the permissible limit, cleaning the groove, and applying primer. Grouting cracks involves fixing injection nipples, injecting grout, and cutting the nipples once the system is cured. Placing of reinforcement involves providing and inserting steel shear key bars, drilling holes, cleaning the holes, injecting epoxy, and allowing the shear key bar to stay undisturbed for 24 hours. Placing of new reinforcement involves applying adhesive to the concrete surface, applying polymer-modified bonding cement slurry, providing and fixing special watertight centring and shuttering, and laying reinforced concrete for the pier wall. Curing and de shuttering involves covering all exposed surfaces of concrete with moist gunny bags or any other approved material, keeping the exposed surfaces continuously damp after the final set, and de-shuttering and starting curing after the specified time by the Engineer. These constrained steps have been followed at the site and can be seen in figure 8.

Fig. 7. Schematic step-wise procedure for Implementing recommended restrengthening technique;

However, the implementation of this restrengthening technique poses several challenges. One significant challenge is placing new rebars in the existing structure, requiring careful planning and execution to ensure the rebars are properly placed, anchored, and aligned with the existing structure reinforcement. Another challenge is fixing shear connectors that were placed accurately and securely to ensure proper bonding between the new and existing concrete layers. Due to the limited space and narrow gaps between the shuttering and the existing concrete surface of the member, it can be difficult to ensure that the concrete is evenly distributed and compacted throughout the member, resulting in voids, honeycombing, and other defects that can compromise the strength and durability of the structure. Additionally, the mix's stiffness or fluidity can affect its proper placement and compaction, and environmental factors such as temperature, humidity, and wind speed can affect the concrete's setting time and curing, leading to cracks, shrinkage, and other problems.