Experiments on cyclic performance of external diaphragm joints between CFDST columns and steel beams

External diaphragm joint has been widely used in concrete-filled steel tubular (CFST) structure because of its large stiffness, good plasticity, and high bearing capacity. This paper studied new external diaphragm joints designed to connect concrete-filled double steel tubular (CFDST) columns and steel beams. Experiments were conducted to investigate the cyclic performance of nine joint specimens subject to cyclic horizontal load and fixed axial load at the top of the column. The variable parameters considered in the test were axial load of the CFDST column, width of external diaphragm, configuration of anchorage web and beam to column bending stiffness ratio. The load–displacement hysteresis behaviors were discussed. Failure mode of the joints was mainly dependent on beam to column bending stiffness ratio (k) and axial compression ratio (n), so the limit of these two factors should be considered to avoid the column failure in engineering design applications. The shear strain level in panel zone was high especially for weak-column joints. Results also showed that initial stiffness of external diaphragm joint significantly increased with the improvement of axial compression ratio, but the stiffness suffered a sharp degradation; the ductility and energy absorption ability improved with the width improvement of the external diaphragm; ribbed anchorage webs effectively improved initial stiffness and bearing capacity of external diaphragm joints.