Effects of chord pre-load on strength of CHS X-joints stiffened with external ring stiffeners and gusset plates

摘要

Compared to unstiffened circular hollow section (CHS) X-joints, CHS X-joints stiffened with external ring stiffeners and gusset plates have exhibited much higher bearing capacity. To gain insight into the effects of the chord pre-loads on ultimate bearing capacity, this paper presents results of finite element (FE) analyses of the stiffened X-joints with braces under compression and chord under (i) axial load, (ii) in-plane bending moment, or (iii) combinations of axial load and in-plane bending moment. Precision of the FE model under combined brace and chord loads is validated by test results. The ultimate bearing capacities attained by using proportional loading and non-proportional loading respectively are presented, and the results indicate that the differences due to loading path are negligible. The validated FE modelling technologies are then employed in a parametric study on the effect of chord pre-load. A total of 4560 stiffened X-joints are examined in the parametric study. The theoretical analysis presented herein provides a reasonable explanation for the significant reduction in strength of stiffened X-joint when the chord is under axial tension. Finally, a chord stress function with corresponding boundary conditions is proposed, in which the coefficients for different chord load caws are determined through regression analysis. Furthermore, a lower-bound multiplier is given for the function to ensure a conservative design.