Effect of Brace-to-Chord Angle on Performance of Unstiffened Circular Hollow Section X-Joints under Brace Axial Force

In order to study the effect of brace-to-chord angle (BCA) on the performance of unstiffened circular hollow section (CHS) X-joints under brace axial force, experimental test was carried out to verified finite element (FE) model. Then FE parameter analysis were used to study the effect of BCA on the stress transfer and bearing capacity of the X-joints under brace axial force, and the capacity prediction accuracy of the X-joints with small BCA was improved. The results show that the failure pattern of test is local buckling of chord wall near brace-to-chord intersection. The incline X-joints (brace-to-chord non-orthogonal) with BCA greater than 60° have the similar stress transfer characteristic to that of the brace-to-chord orthogonal X-joints, which is consistent with the assumption of the Togo model. Moreover, the reciprocal of the sine of BCA (RSBCA) in the current specification can accurately reflect the influence of BCA on the capacity. However, the stress transfer characteristics of the incline X-joints with BCA less than 45° are quite different from the assumption of the Togo model, and RSBCA underestimates the beneficial effect of BCA on the capacity of these X-joints (even 30% for the X-joint with BCA near to 30°). Hence, it is recommended to multiply a correction coefficient on the existing capacity prediction formula of these CHS X-joints with BCA less than 45°, to improve the prediction accuracy.