Seismic Performance of Steel Beams to Diamond-Shaped Concrete-Filled Steel Tube Column Connections: Concept and Validation

Abstract

The brittle behavior traditional directly welded connections of steel beams to concrete-filled steel tube columns is caused primarily by excessive out-of-plane deformation of the tube walls at the level of the beam tension flange. To address this issue, this study proposes a reference connection that involves fillet welding a built-up steel beam directly to the corner of a diamond-shaped concrete-filled steel tube (DCFST) column. Two options are suggested for enhancing the seismic performance of the reference connection: a predrilled hole with a 12-mm diameter at the midwidth of each beam flange, or a rib stiffener reinforcement on the outside of each beam flange. The two proposed specimens and a traditional directly welded connection were subassembled and investigated experimentally. The results showed that the reference DCFST connection significantly improved the seismic response of the directly welded connection in terms of initial stiffness, strength, ductility, and energy-dissipating capacity. Specifically, the initial stiffness and strength capacity increased by over 150% compared with that of the traditional connection counterpart. Furthermore, the rib stiffeners contributed to further enhancement of the seismic response by shifting the beam plastic hinge away from the column face. Overall, these findings suggest that the use of DCFST connections is reliable for composite moment-resisting frames (C-MRFs), and the proposed enhancements can improve the seismic performance of these connections significantly.