LAUSR

Abstract This paper presents a comprehensive investigation of the hysteretic behavior of unstiffened circular hollow section (CHS) X-connections subjected to out-of-plane bending moment (OPBM). The study commences with tests on three full-scale CHS X-connection specimens with varying geometric parameters. The test results showed that the specimens mainly failed in tearing of the chord wall near the connection zone. Evident energy dissipation was provided when the connections experienced yielding, and this was followed by ductile crack propagation of the chord wall. The strength and ductility of the connections depended significantly on the brace-to-chord diameter ratio and the in-plane brace-to-chord angle. In particular, a decrease in the brace-to-chord angle led to increases in both the strength and connection efficiency (i.e., the ratio of the connection ultimate flexural capacity to nominal brace flexural yielding capacity) of the connection specimens. The test results also suggested that the current design code tends to make conservative predictions of the OPBM capacity of the connections, especially when the in-plane brace-to-chord angle is small. Moreover, either decreasing the in-plane brace-to-chord angle or increasing the brace-to-chord diameter ratio is found to benefit the ductility ratio and energy dissipation capability. This observation is further confirmed by a ring analytical model proposed in this study. FE models are then built and calibrated through comparisons against the test results, and subsequently, a parametric study was carried out to consider the influences of an extended range of geometric parameters.