Experimental and numerical analysis of the stress concentration factor for concrete-filled square hollow section Y-joints

Previous studies have shown that the stress concentration factors for 90° square hollow section T- and X-joints can be significantly reduced by filling the chord with concrete and stiffening the chord with perfobond ribs. The current study examined stress concentration factors for non-90° (Y-type) joints. A total of 11 Y-joints were tested under axial tension, and the hot spot stresses were measured. The measured results were employed to evaluate the influence of design parameters on the stress concentrations. In addition, the measured results were used to evaluate finite element models. A parametric study was then undertaken using the finite element models to generate an extensive database of stress concentration factors and to develop parametric design equations to estimate the maximum stress concentration factors on the brace and the chord of concrete-filled square hollow section Y-joints with perfobond ribs. It was found that decreases of 13.7%–59.9% in the stress concentration factors occurred in concrete-filled square hollow section Y-joints stiffened by perfobond ribs relative to conventional square hollow section joints for different loading cases.