Seismic Behavior of Π-Shaped Connector RC Beam–Column Joints: Experimental and Numerical Investigation

Abstract

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.