Behavior of Concrete-Filled U-Shaped Steel Beam to CFSST Column Connections

Two new types of connection between concrete-filled U-shaped steel (CFUS) beams and concrete-filled square steel tube (CFSST) columns were presented in this study, including rebar-sleeve with internal diaphragm connection and rebar-through with internal diaphragm connection. Based on the experiments of the rebar-plate with internal diaphragm connections between CFUS beams and CFSST columns under cyclic loading, the nonlinear finite element models of the tested specimens were developed and validated by comparing them with the experimental results. The numerical results were in agreement with the experimental results in terms of failure modes, stress distribution, and load-displacement skeleton curves. Based on the FEA results, the mechanical behavior of the two new types of connection were comprehensively discussed and compared. Furthermore, this parametric study was conducted for the rebar-sleeve with internal diaphragm connection to investigate the effect of specific parameters on the capacity of the connection. The parameters included: The thickness of U-shaped steel, the ratio of longitudinal reinforcement in the concrete slab, the strength of concrete in the beam, the strength of the U-shaped steel, and the thickness of the internal diaphragm. The results indicate that the thickness of the U-shaped steel (tb), the ratio of the longitudinal reinforcement in concrete slab (ρ), and the strength of the U-shaped steel have significant effects on the loading capacity of the connection—the loading capacity increases by about 20% when tb increases from 6 mm to 8 mm, increases by about 45% when ρ increases from 1.5% to 4.8% under negative P, and increases by about 20% when the steel yield strength (fy) increases from 235 Mpa to 420 Mpa.

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