Numerical Investigation of Retrofitting Strategies for Existing Reinforced Concrete Beam-Column Joints: A Systematic Review

Abstract

Many existing reinforced-concrete (RC) frames do not have joints which are detailed according to modern seismic detailing provisions. Consequently, the joint core of many existing frames is at risk of experiencing diagonal tension, bond deterioration, bar-slip, loss of stiffness and brittle shear failure. An insightful synthesis of 50 studies from the years 2021 to 2026 involving the numerical investigation and retrofitting of RC beam-column joints, especially methods useful for existing structures. An audit was informed by PRISMA on the corpus supplied: all 50 deduplicated records were screened; four complete open-access papers were audited in full text, and 46 were evaluated through verified publisher, DOI, and abstract-level records. The literature was divided into FRP, steel and mechanically anchored devices, advanced jackets, hybrid and precast connection strategies, SHM, and latest finite-element/explained-machine-learning approaches. Non-linear finite element analysis was applied across the direct evidence – most often based on concrete damage plasticity, non-linear reinforcement constitutive laws and explicit interface or bond assumptions. This was deemed effective when calibrated against full-scale cyclic tests. The results obtained through tests indicate that the performance of retrofit is less dependent on the nominal strength of the materials used, but more so on the modification of the force-path, anchorage, interface behaviour, and confinement, and prevention of premature joint-core shear. According to one numerical study, CFRP improves the ultimate-load by 103.93%, U-shaped bars by 43.55% and pre-tensioned steel-angle strengthening by 148.50%. Furthermore, a post-tensioned metal-strap programme claims a core recasting gave up to 42%, and further strapping up to 25% increase in shear-capacity recovery. According to the account, joint shear deformation was more than 40% less for the combined C-FRP rope-and-sheet strengthening. Further, the peak load was 65% higher as well as 55% higher equivalent viscous damping. Modelling degraded bond, corrosion, bidirectional loading, slab participation, field installation variability, long-term durability, and uncertainty-aware validation has important gaps. The conclusion of the review points out that hybrid, mechanical anchoring and damage-controlled retrofits offer the most reliable route once the design is supported by experimentally justified nonlinear models and performance-based acceptance criteria.

Introduction

This review examines recent advances (2021–2026) in the retrofitting of reinforced concrete (RC) beam-column joints, which are critical components responsible for transferring gravity and earthquake loads in buildings. Many older RC structures lack adequate reinforcement, proper anchorage, and modern seismic design features, making their beam-column joints susceptible to brittle failure during earthquakes. Instead of forming ductile beam hinges, these deficient joints often experience cracking, bar slip, and shear failure, which can lead to premature structural collapse. Consequently, modern research models beam-column joints as non-linear structural subassemblies rather than rigid connections.

The review highlights a wide range of retrofit techniques aimed at improving joint strength, ductility, and seismic performance. Carbon Fibre Reinforced Polymer (CFRP) systems—including sheets, plates, bars, ropes, and near-surface-mounted reinforcement—are among the most widely studied because they provide high tensile strength, corrosion resistance, and minimal increase in structural dimensions. Their effectiveness depends heavily on proper anchorage, fibre orientation, bonding, and surface preparation. Studies show that X-shaped CFRP ropes, grooved reinforcement, and combined rope-sheet systems effectively improve joint confinement, shear resistance, and energy dissipation while encouraging ductile beam failure rather than brittle joint failure.

Where FRP systems are less suitable due to anchorage, fire resistance, or substrate limitations, steel-based retrofit methods such as steel plates, haunches, prestressed straps, and steel angles provide effective alternatives. These systems create external load paths that redistribute stresses and enhance joint performance, although their behaviour depends on factors such as bolt pretension, welding quality, and interaction with the existing structure. Advanced cementitious materials, including UHPFRC and strain-hardening composites, further improve crack control and cyclic stability but require careful modelling of the interface between old and new materials.

The review notes that existing research is extensive but fragmented, covering different joint types, retrofit materials, numerical models, and experimental methods. The authors therefore aim to classify retrofit technologies, compare modelling approaches, identify reported performance improvements, distinguish well-supported findings from limited evidence, and define future research priorities for practical, performance-based retrofit design.

A systematic PRISMA-informed review of 50 peer-reviewed studies published between 2021 and 2026 was conducted. The review used predefined inclusion and exclusion criteria and classified studies into five categories: conventional repair, FRP/CFRP strengthening, steel-based strengthening, advanced cementitious and hybrid systems, and emerging approaches such as structural health monitoring and machine learning.

The review finds that non-linear finite element modelling has become essential for accurately predicting joint behaviour. Modern simulations commonly use three-dimensional continuum models, concrete damage plasticity, cyclic bond-slip laws, embedded reinforcement, and displacement-controlled loading to reproduce stiffness degradation, crack propagation, energy dissipation, and failure mechanisms. The reliability of these models depends strongly on realistic representation of material interfaces, bond-slip behaviour, anchorage conditions, and prior structural damage rather than assuming perfect bonding between retrofit materials and existing concrete.

Among the reviewed retrofit methods, prestressed steel-angle systems produced the largest reported increase in ultimate load capacity (up to 148.5%), followed by CFRP systems (approximately 104%) and U-shaped steel bars (approximately 44%). These techniques were also effective in relocating failure from the joint to the beam, achieving the desired ductile seismic response. However, direct comparison across studies remains difficult because of differences in specimen geometry, reinforcement deficiencies, loading protocols, and modelling assumptions.

The review concludes that successful beam-column joint retrofitting requires more than increasing shear strength. Effective retrofits must preserve the global seismic load path, promote beam hinging, prevent brittle joint failure, and avoid transferring excessive demands to columns or foundations. Future research should focus on validated numerical models that incorporate realistic bond-slip behaviour, interface damage, corrosion, construction tolerances, bidirectional earthquake loading, and long-term structural performance to support reliable, field-ready seismic retrofit design.

Conclusion

An examination of repairs, strengthening and transferable seismic design for reinforced-concrete beam-column joints of existing structures will be performed to carry out a systematic review of 50 studies published from 2021 to 2026. According to the literature, the systems can be organised into the FRP/composite systems, steel and mechanically anchored devices, advanced cementitious jackets, hybrid and damage-resilient connections, and monitoring/data-driven methods. Nonlinear finite-element analysis is a powerful retrofit-development tool when calibrated against realistic cyclic tests and explicit representation of concrete, reinforcement, interface, anchorage and prior-damage mechanisms, the evidence shows. Performance-based decisions cannot be taken with only peak strength compatibility. The models are also insufficient if they model other effects such as stiffness degradation, pinching, shear deformation, and failure location failure location. The addition of FRP sheets, plates, bars and rope is highly efficient and very light. X-shaped NSM ropes, grooving and combined rope/sheet arrangements improve load-path definition and reduce reliance on surface adhesion. Steel angles, haunches, plates, straps and prestressed devices provide mechanically anchored and inspectable force transfer. A pretensioned steel-angle system produced an ultimate-load increase of 148.50%, as per the audited full-text evidence, compared with 103.93% for CFRP and 43.55% for U-shaped bars. Through core recasting and PTMS, the parameter’s joint shear capacity is recovered by 42%. The further increase in joint shear capacity was up to 25%. With combined wrap of C-FRP ropes and sheets, peak load increased by 65%. The equivalent viscous damping increased by 55%. Joint shear deformation decreased by… Continue Reading Past Studies and Experimental Observations on Joint Shear Behaviour of FRP-Confinement RC Joint at High Drift Levels 543 Over 40%. Strength retention at 4%? drift was more than 90%. The ECC, UHPFRC, HPFRCC, and FRCM systems are especially suitable for the damaged cover replacement, crack control, durability, and fire compatibility requirement. Among the main research gaps that have been identified are cyclic interface modelling, corrosion and prior-damage representation, biaxial loading, slab and transverse-beam participation, environmental ageing, construction tolerances, blind validation, and transfer from subassembly response to complete-building performance. The future research efforts should aim at establishing new open benchmark datasets, uncertainty-aware multiscale models, and standardized measure of performance. This review’s primary contribution is a traceable mechanism-based synthesis which distinguishes verified numeric evidence from unreported information and shows that the most reliable retrofit is not the strongest material but one that provides a reliable ductile load path, controls damage at large drift, and remains verifiable during construction and service.

References

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Copyright

Copyright © 2026 Yash D. Wani, Umesh L. Deshpande, Rais A. Chougale. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.