Study on seismic behavior of CHS T-joints under quasi-static cyclic in-plane bending

This paper aim to study the in-plane flexural behaviors of circular hollow section (CHS) T-joints by quasi-static cyclic loading test and finite element (FE) analysis. Two specimens under cyclic in-plane bending (IPB) were carried out to investigate the effect of the brace-to-chord diameter ratios (a key parameter for the CHS joints and denoted as beta) on the seismic behaviors of the T-joints. Moreover, finite element (FE) analysis were performed to study the effect of beta, gamma (another key parameter for the joints with name of the chord radius-to-thickness ratio) and the chord axial pressure on the in-plane flexural behavior of the T-joints. Test results showed that both two specimens failed in tearing of the chord wall at the heat-affected zone (WHAZ), and both two specimens exhibit good ductility and energy dissipation behavior. Both specimens mainly rely on the plastic development of the chord wall near brace/chord intersection and the crack propagation (after cracking) to dissipate energy input by the earthquake. Test results also found that the current specification conservatively predict the in-plane flexural strength of the T-joints (about 20 %-30 %), especially for the joints with larger beta. Test and FE results also show that the increase of beta (or the decrease of gamma) will effectively improve the flexural strength, energy dissipation capacity and ductility ratio. The results also shows that chord pressure stress will adversely affect the in-plane flexural behavior of the T-joints, especially when the stress is larger than 0.6 times of the chord yield strength. A FE parametric study was performed to investigate the effect of beta on the force transmission charac-teristics of the T-joints under IPB, and the force transmission characteristics in elastic state was further inter-preted by a simple semi-circular arch analytical model.