Experimental Study On Seismic Behavior Of Moment Connections Of Steel Beams To Circular Concrete-filled Steel Tube Columns

With the rapid development of super tall buildings, frame-core tubestructural system has been widely used in China. The peripheral frame offrame-core tube structure can be various forms, such as steel frame, reinforcedconcrete frame, steel beam-circular (or rectangle) concrete-filled steel tubecolumn frame, and steel beam-steel reinforced concrete column frame. Forsteel beam-circular concrete-filled steel tube column frame, the mechanicalbehavior of beam-column connections is the key to whether the peripheralframe can be the second seismic defensive line of the structure or not.Nowadays, domestic experimental studies on beam-column connections focuson connections with diaphragm plates inside or outside circular steel tube. Tostudy seismic behavior of through beam connection or other types of steelbeam to circular concrete-filled steel tube column, which is on the background of Beijing Treasure Center Tower2, quasi-static test of five large-scalejoint specimens were conducted. Among the five specimens three are throughbeam connection specimens and two are inside diaphragm plate connectionspecimens. The former three specimens are standard type, flange weakenedtype and flange enlarged type, respectively. The latter two include a specimenwith beam flange cover plates and a specimen with special enlarged beamflanges.The test results indicate that the failure modes of through beamconnection specimens are fracturing between the groove welds at the end ofbeam flange and steel tube, and local buckling of beam flanges; peak bearingcapacity and yield secant stiffness of flange weakened type specimen are bothsmaller than that of standard type specimen, enlarging of beam flanges haslittle positive effect on improving peak bearing capacity and yield secantstiffness; through beam connection specimens have a large elastic-plasticdeformation capacity and the ultimate rotation reaches0.04; the beam endmoment-rotation hysteretic loops of through beam connection specimens are plump, showing good ability of energy dissipation; for specimen with beamflange cover plates, fracture occurs at the weld between the beam end and thesteel tube, which weakens its seismic behavior; the special flange enlargedspecimen shows good seismic behavior, but brittle fracture appears at thecorner where the flange width changed. Furthermore, non-linear finite elementanalysis of five specimens was performed based on the general FEA programANSYS11.0. The predicted results of through beam connection specimens arevery similar with the measured results. The through beam connection withflange weakened specimen shift the plastic hinge outwards apparently, whilethe flange enlarged specimen also shifts its plastic hinge outwards.Based on the results of experiments and FEA analysis, it is recommendedto use the standard type of through beam connections between steel beams andcircular concrete-filled steel tube columns, the flange weakened type and theflange enlarged type of through beam connections are preferred if shifting thebeam plastic hinge is required.