Experimental seismic behavior of bottom-through-diaphragm and top-ring plate connection to STMB columns

This paper introduces a novel type of connection characterized by a bottom-through-diaphragm and top-ring plate (BTD-TRP) to T-shaped multi-box (STMB) columns. To investigate the seismic behavior of this connection, six full-scale specimens were evaluated, based on various factors such as vertical stiffener plate, thicknesses of STMB columns, reduced beam section (RBS), beam depth, and STMB column connection style. The evaluation covered seismic behavior parameters, including hysteretic curves, panel zone deformation, skeleton curves, ductility, stiffness degradation, energy dissipation, and strain distributions. According to the test results, the new connection demonstrated reliable energy dissipation capacity, and the connection’s rotation met the requirements of the Chinese seismic standard for steel frames, with maximum story drift angles greater than 0.02 rad. The dominant failure mode was the fracture of the complete joint penetration (CJP) weld between the TRP and the flange, occurring after local buckling of the beam. Additionally, a finite element model (FEM) was developed and validated, revealing he load transfer mechanism. Experimental and FEM results indicate that the boundary box of the STMB columns, connected to the beam, bore most of the bending moment. High-stress areas were concentrated in the area connecting the beam’s flanges to the BTD and TRP, and the area near the corner of the TRP and BTD adjacent to the boundary box. Finally, a comparison of the BTD-TRP connections between the square steel tube (SST) and STMB columns to further investigate this new type connection. This study could serve as a reference for seismic provisions related to this type of connection.