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Based on the low cyclic loading test results of vertical stiffener joints between concrete-filled double steel tubular (CFDST) columns and steel beams, the shear transfer mechanism and shear resistance were analyzed in this paper. A conceptual model formulated was presented in terms of equilibrium and stress-strain relationships. The results calculated by the theoretical model and the available experimental data were compared, and then one new concept of shear storage coefficient was proposed for the determination of the shear storage capacity of the joint, which quantitatively explained the ductility failure progression of the joint specimens in the seismic performance test. It was concluded that the vertical stiffener joint had sufficient shear resistance, which met the seismic design principle of strong shear and weak bending. Results show that the ribbed joints have greater shear resistance than unribbed ones; lengthening the overhang of the vertical stiffener can both increase shear resistance and shear storage capacity of the joint; axial compression ratio can reduce the shear storage capacity. The paper also suggests that the joint design should ensure enough safety storage of shear resistance to improve the seismic performance.

External diaphragm joints with high structural reliability are used widely in composite steel and concrete structures. In this study, the external diaphragm joint was improved to be a steel beam-to-concrete filled double steel tubular column connection. The digital speckle correlation method was used to measure and investigate the strain field in the panel zone and relative beam-to-column rotation in a low-cycle reciprocating loading test. The obtained hysteresis curves of moment-rotation ( M-θ) and shear force-deformation ( V-[Formula: see text]) showed that the external diaphragm joints had higher strength, higher ductility, and better energy dissipation capacity. Decreasing the axial compression ratio resulted in the deterioration of initial rotational stiffness. Wider external diaphragm produced better ductility and larger initial shear stiffness. The ribbed anchorage web was effective to increase the bending resistance by 10%. Beam-to-column bending stiffness ratio can not only influence the bending resistance and energy dissipation capacity significantly but also affect the shear deformation capacity in the joint core. The magnitude of the shear strain in the panel zone was large, especially for the specimens under column failure mode, and shear deformation in the panel zone should not be neglected for it accounted for 30%–40% of the beam-to-column rotation. Beam-to-column rotation and shear deformation obtained by the digital speckle correlation method offered better predictions to analyze the mechanical behavior of external diaphragm joints in the concrete filled double steel tubular structures.

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is paper firstly studied the internal force transfer mechanism of vertical stiffener joints in concrete-filled double steel tubular (CFDST) frame structures on the basis of finite element modeling (FEM). Analytical models of shear force and bending moment were established through the appropriate material constitutive equations and equilibrium theory. en, the proposed models were used to predict and evaluate the shear and bending resistance of the vertical stiffener joint. Six joint specimens were tested to verify the rationality of the theoretical models, and the design suggestions for construction were subsequently discussed. e analysis indicated that the vertical stiffener together with the anchorage web played a dominated role in the internal force transfer mechanism. e computed bending resistance obtained by the tension model agreed well with the measured experimental data, and the shear resistance in the panel zone was sufficient to guarantee the ductile failure in the test. e vertical stiffener determined the plastic hinge so as to ensure the strong connection between the CFDST column and the steel beam. e ribbed anchorage web was an effective way of increasing the shear and bending resistance.