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