Seismic behaviour of composite concrete-filled tube column-to-beam moment connections

This paper describes the results of cyclic loading applied to seven square concrete-filled tube column-to-beam connections. Connections of all seven specimens were reinforced with T-shaped stiffeners attached to the beam flanges. The specimens are divided into three series: the TS series specimens were reinforced with T-shaped stiffeners only; those in the TSD series had RBS beams in addition to the stiffeners; and those in the TSH series had small holes in the stiffeners. The test results presented in terms of the ductility capacity of the test specimens. All the specimens developed plastic rotations in excess of 3% rad, suggesting that the ductility capacity of the specimens exceeds the requirements for special moment frame connections in the AISC seismic provisions. The tapered horizontal stiffener elements, RBS cutouts and the horizontal stiffener holes were effective in reducing the stress concentration at the tip of the horizontal element. However, some of the specimens failed by a premature fracture in the HAZ of vertical element welds, suggesting that in designing the T-stiffeners strain hardening should be considered.