Influence of brace-to-chord angle on the seismic behavior of circular hollow section X-joints under in-plane bending

Abstract

This paper studied the influence of brace-to-chord angle (BCA) on the in-plane flexural behavior of circular hollow section (CHS) tubular X-joints. The study begins with three CHS tubular X-joint specimens (one orthogonal joint with BCA of 90°, two skew joints with BCA of 70° and 55° respectively) under cyclic in-plane bending moment (IPBM). The test results showed that specimens mainly failed in tearing of the chord wall near the brace/chord intersection after experienced large plastic development, and the crack propagation rate of the chord wall of the skew specimens under negative IPBM is obviously faster than that under positive IPBM, while the propagation rates of the orthogonal specimen under two IPBM is similar. The ductility, strength and energy dissipation of the X-joints are deeply affected by BCA. Decreasing BCA is beneficial to the ductility ratio under positive IPBM, but it is not conducive to the ductility ratio under negative IPBM; decreasing BCA can increasing the flexural strength; both the skew joint with large BCA and the orthogonal joint exhibit higher energy dissipation behavior than that of the skew joint with small BCA. These observations is further confirmed by a simple load transferring model proposed in this study. Finite element (FE) parametric analysis is then carried out to verify test and the load transferring mechanism analysis results. Moreover, FE and test results showed that the negative strength Miu− (under negative IPBM) and the positive strength Miu+ (under positive IPBM) of the orthogonal joints are close, but Miu− of the skew joints are larger than the counterpart of Miu+, and the ratio of Miu− /Miu+ is increased (from slightly more than 1.0 to above 1.2) as BCA decreased (from 70° to 35°).