Seismic performance of diaphragm-through type joints between concrete-filled square steel tubular column and H-section steel beam with enlarged arc and dog-bone junctures

In order to study the effects of enlarged arc and dog-bone junctures on seismic performance of diaphragm-through type joints between concrete-filled square steel tubular column and H-section steel beams, low-reversed loading tests were performed on joints with enlarged arc and dog-bone junctures as well as conventional joints. Disaster mechanism analysis was performed on the specimens based on an elliptical fracture envelop and a generalized yield model of constructional steel. The results of tests and fracture analysis reveal that crack initiates at the edges of constructional welding holes of beam web. The core concrete in panel zone acts as a baroclinic short column and does not crack or crush until joints failure. The conventional joint exhibits brittle fractures at the edges of butt weld between the beam flange and the diaphragm rib with the sharply changed geometry where the stress concentration is serious. The plastic rotation of the conventional joint is about 0.016 rad. For the joints with enlarged arc and dog-bone junctures, the plastic hinge is formed at the reduced beam section far away from panel zone while the sharply changed geometry and stress concentration at butt weld of beam flanges are mitigated. The plastic rotation of joints with enlarged arc and dog-bone junctures may range from 0.033 rad to 0.041 rad, and the energy dissipation capacity increases by 72%~86% while the load bearing capacity decreases by 9.6%~12.6%, compared with that of conventional joints.