Bi-directional seismic behavior of steel beam-column connections with outer annular stiffener

This paper investigates the seismic behavior of steel beam-column connections with outer annular stiffener under bi-directional cyclic loadings. Five welded three-dimensional beam-column connections configurated by hollow square structural steel (HSS) column sections, H-shaped steel beams, and outer annular stiffener was tested. The main parameters considered in this experimental study include loading protocols (anti-symmetric bidirectional and unidirectional cyclic reversals), beam depths, and the leg size of fillet weld between the outer annular stiffener and column. Moment versus rotation hysteretic responses, skeleton curves, stiffness degradation, and the associated energy-dissipating capacity were analyzed. The hysteretic loops of all specimens show a stable and ductile performance indicating a good energy-dissipating capacity. The ultimate flexural strength under the unidirectional cyclic reversals was found to be 20% higher than that under the corresponding bi-directional loading history. As the fillet weld leg size increases from 6 mm to 10.2 mm, the ultimate flexural capacity of the beam ends is slightly enhanced. The beam depth is a major factor that controls the elastic stiffness and strength capacity of the outer annular stiffener. The ductile failure mode can be achieved by using the proposed equations for the strength calculation of ring stiffeners.