Semi-rigidity Connection Model for Unstiffened CHS X-type Joints Subjected Out-of-plane Bending

Mechanical performance of unstiffened circular hollow section (CHS) multi-planar X-joints subjected two different directions (sagging and hogging) of out-of-plane bending moment (OPBM) was analyzed. A seven-parameter exponential function model, which describing semi-rigidity behavior (moment-rotation curves) of the X-joints subjected sagging and hogging OPBM, was proposed, and then the method to obtain the values of each parameters in the seven- parameter model was also proposed. Based on the results of FE parametric analysis, formulas for parameters in the seven-parameter model were established combined with multiple nonlinear regression analysis. FE and test results were used to verified the seven-parameter model. The results indicated that: the seven-parameter model can well reflect the semi-rigidity behavior of CHS multi-planar X-joints subjected to OPBM.