COMPARISON OF IN-PLANE FLEXURAL SEISMIC BEHAVIOR BETWEEN CHS CROSS-TYPE JOINTS AND CHS T-JOINTS

Current codes believe that the in-plane flexural strength of T-joints with unstiffened circular hollow sections (CHS) is the same as that of cross-type joints with corresponding CHS. However, the force characteristics of the former is different from the later. In order to comprehensively compare the behavior of the cross-type joints and the T-joints under in-plane bending (IPB) conditions, the experimental test of six CHS joints (four cross-type joints and two T-joints) under cyclic IPB conditions are carried out, and force mechanism analysis and finite element analysis are also carried out. The four cross-type joints stay in two loading conditions, which including a reverse bending loading condition and a syntropy bending loading condition. The results show that: the failure mode of each joint is the ductile tearing of the chord wall near the intersection, and all joints exhibit good seismic performances. Regardless of the T-joints or the cross-type joints, increasing β (brace-to-chord diameter ratio) can significantly improve its strength, ductility and, energy dissipation capacity. Comparing T-joints and the corresponding cross-type joints, the former has higher flexural strength than the latter, but its ductility is not as good as the latter, and its energy dissipation capacity is between the energy dissipation capacities of the cross-type joints under two IPB loading conditions. Contrast with the reverse bending loading condition, the syntropy bending loading condition is detrimental to the in-plane flexural behavior (e.g., strength, energy dissipation and ductility) of the cross-type joints with smaller β (close to and less than 0.7), but the syntropy bending loading condition is beneficial to the behavior of cross-type joints with a larger β (close to and larger than 0.9).