Bi-Directional Loading Tests of Weak Panel-Type Subassemblies Consisting of Circular-Hollow-Section Columns and H-Beams with Floor Slab

Since panel zones in steel moment-resisting frames can yield during large earthquakes, it is worthwhile to investigate their elasto-plastic behavior. Previous studies mainly investigated the effects of axial force on the panels or the panel aspect ratio (panel length divided by panel diameter) on the behavior of the panel zones. However, there are no such studies on panel zones with circular hollow sections and the effect of floor slabs has rarely been studied. Against this background, this study examines the effect of floor slabs on the behavior of panel zones with circular hollow sections using a cyclic loading test of three-dimensional cruciform subassemblies. The test parameters are the presence of a floor slab, the panel aspect ratio, and the direction of horizontal force. The test results show that in all cases, the horizontal force-story drift relationships were stable up to large deformations with story drifts greater than 6%. Moreover, the plastic strength of the specimens with a floor slab increased by 21% to 46% compared to that of the specimens without a floor slab. The increase in plastic strength was large when the panel aspect ratio was small and the horizontal force was applied in the in-plane direction.