To enhance the seismic performance of existing reinforced concrete (RC) buildings during retrofitting, the study introduces a new type of joint connected by a T-shaped steel plate. Compared with previous similar strengthening methods, this novel structure incorporating a post-installed beam not only effectively improves the mechanical properties of RC columns, but the connectors also further enhance the integrity of the post-installed beam. Low-cycle reversed loading tests on one cast-in-place specimen (RC) and three T-shaped steel plate connection specimens (TRC1–TRC3) were conducted to evaluate failure modes, hysteresis and skeleton curves, and energy dissipation. Results show that the novel joint failure concentrates at beam-end–column steel jacket weld seams and column-side steel plate cracking, while the core-zone concrete remains intact. Compared with RC, the novel joints TRC1–TRC3 exhibit bearing capacity variations of −1.03%~+15.80% and significantly enhanced energy dissipation. The thickness of the beam’s wrapped steel improves the carrying capacity and energy dissipation, whereas the T-shaped connector thickness has limited influence on bearing capacity. ABAQUS parametric analysis indicates that bolt quantity, concrete strength, and connector thickness have limited influence and serve as secondary design factors. These findings provide a theoretical basis for retrofitting existing buildings.
Numerous existing RC frame buildings in China suffer from seismic deficiencies. This paper proposes a novel Π-shaped connector connection joint for the rapid strengthening of existing beam–column joints: steel plates are wrapped around existing columns, and Π-shaped connectors are welded to link new beam reinforcement. Quasi-static cyclic loading tests were conducted on one RC reference specimen and three strengthened specimens. The strengthened joints showed varying performance—two specimens (JGJ1 and JGJ2) exhibited peak loads below the RC reference, while the best specimen (JGJ3) achieved 9.8% enhancement in peak load and a nearly threefold increase in cumulative energy dissipation. The failure mode transitioned from brittle concrete crushing in the RC specimen to weld cracking and bolt fracture in the strengthened joints, thereby preserving the integrity of the core concrete. Finite element models were established using ABAQUS and validated against the test data. A parametric study investigated the effects of bolt quantity, beam and column dimensions, concrete strength, and steel plate thickness. The FE results indicate that increasing beam height from 400 mm to 450 mm yields the most significant improvement, with peak load increasing by up to 15.59% relative to the base parametric model. Favorable seismic performance was achieved with column concrete grade C50, beam concrete grade C40, steel plate thickness of 6 mm, eight bolts, and connector thickness of 6 mm. The proposed connection provides a potential strengthening alternative for existing RC frame structures.
