Effect of loading patterns on in-plane flexural hysteretic performance of CHS X-connections

Abstract

This paper presents an experimental investigations to study the hysteretic behavior of circular hollow section (CHS) X-connections which widely applied in various tubular structures. Cyclic in-plane bending moment (IPBM) loading patterns and geometric parameter of brace-to-chord diameter ratio (β) were varied in testing four connection specimens, to evaluate the influence of load patterns on the hysteretic behavior of the connections. Test results shown that regardless of load patterns and connection details, all specimens showed plump and no pinching effect for the hysteresis curve before cracking occurred, all specimens shared similar final failure modes (the chord wall near the intersection teared) and similar energy dissipation modes (mainly rely on the plastic deformation of the chord wall near the intersection). However, the influence of loading patterns on the hysteretic behavior of the X-connections with varied β is different. For the CHS X-connections with large β, it developed higher flexural strength, better ductility and more energy dissipation performance under synchronized down and up IPBM (SDUI) loading pattern than that under take turns to align clockwise and counterclockwise IBPM (TCCI) loading pattern; while for the X-connections with small β, it is opposite. This experimental observation result was further affirmed by a simplified analytical model and FE analysis results. The test results also indicated that regardless of the load patterns, increasing β trend to significantly improve the strength, ductility ratio and energy dissipation behavior of CHS X-connections under cyclic IPBM, and the current specification trend to give conservative prediction on the in-plane flexural strength of the X-connections.