Addressing the critical seismic vulnerabilities of reinforced concrete (RC) beam-column joints remains an imperative research priority in earthquake engineering. This study presents an experimental and analytical investigation into the seismic performance enhancement of non-ductile RC frames using an innovative all-steel Tube-in-Tube Buckling-Restrained Brace (TnT BRB) system. Shake table tests were performed on one-third scale RC frame specimens, including a baseline structure representing conventional substandard design and a counterpart retrofitted with the proposed TnT BRBs. Experimental results revealed that the unretrofitted specimen experienced pronounced brittle shear failures, excessive lateral deformations, and significant degradation of beam-column joints under cyclic seismic loading. In contrast, the TnT BRB-retrofitted specimen exhibited substantially improved seismic behavior, characterized by enhanced energy dissipation, controlled inter-story drifts, and preserved joint integrity. Advanced fiber-based finite element modeling complemented the experimental efforts, accurately capturing critical nonlinear phenomena such as hysteretic energy dissipation, stiffness degradation, and localized damage evolution within the structural components. Despite inherent modeling limitations regarding bond-slip effects and micro-level cracking, strong correlation between numerical and experimental results affirmed the efficacy of the TnT BRB retrofit solution. This integrated experimental-analytical approach offers a robust, cost-effective pathway for upgrading seismically deficient RC structures in earthquake-prone regions.

The process of seismic retrofitting for inadequate RC frames is vital for enhancing structural integrity in areas susceptible to earthquakes. This research investigates a novel tube-in-tube (TnT) buckling restrained brace (BRB) system aimed at improving the seismic performance of these substandard RC frames. By targeting significant weaknesses inherent in older RC constructions, the TnT BRB introduces a lightweight, all-steel configuration that eliminates the need for traditional mortar or concrete infill materials. Experimental shake table testing on two one-third scaled RC frame models was conducted to compare the seismic performance of an unretrofitted control frame and a frame retrofitted with the TnT BRB system. Results indicate significant enhancements in lateral strength, ductility, and energy dissipation capacity in the retrofitted frame, demonstrating stable and symmetrical hysteresis loops and reduced stiffness degradation compared to conventional X-braced systems. Analytical modeling corroborated these experimental findings, confirming the TnT BRB’s superior capability in absorbing seismic energy and preventing premature structural failures. This investigation emphasizes both the practical and financial benefits of integrating the TnT BRB into seismic retrofitting strategies while recommending further research to optimize the system, specifically addressing issues related to local denting, frictional wear, and alignment to bolster its effectiveness in practical applications.