Hysteretic Behavior of Circular Hollow Section Panel Zones in Beam-to-Column Subassemblies with Large Panel Aspect Ratio

This paper aims to comprehend the behavioral aspects of beam-to-column subassemblies with highly dissipative circular hollow section (CHS) panel zones with emphasis on those with large panel aspect ratios (i.e., greater than 1.5) via experiments and continuum finite-element simulations. The test results suggest that all specimens exhibited stable hysteretic behavior up to a story drift ratio of 0.06 rad without experiencing strength deterioration, which is an important finding from a collapse safety standpoint. The contribution of the panel zone deformation to the story drift ratio ranged from 40% to 72%. The observed ultimate failure modes as well as the plastic shear strength of the CHS panel zone highly depend on the lateral force orientation and the panel aspect ratio that controls the flexural demands on the panel zone itself. Complementary finite-element analyses suggested that the shear stress distribution in the circumferential direction within the panel zone is nonuniform once yielding occurs, which contradicts the primary assumptions of the panel zone design formula that are tailored for panel aspect ratios from 0.9 to 1.8. A refined reduced-order CHS panel zone model was also proposed that reliably predicts the three-dimensional hysteretic response of subassemblies with dissipative CHS panel zones, regardless of the panel aspect ratio, the lateral force orientation and the axial force ratio and can further facilitate system-level studies at a viable computational cost.