Effects of brace-to-chord angle on capacity of multi-planar CHS X-joints under out-of-plane bending moments

摘要

In order to extend the existing capacity equations under out-of-plane bending moments (OPBM) from uniplanar unstiffened circular hollow section (CHS) X-joints to multi-planar CHS X-joints, theoretical and finite element (FE) parameter analysis are performed. Firstly, an analytical capacity equation for the multi-planar X-joints is derived based on ring analytical model, and a spatial effect factor is proposed to reflect the influence of the outof-plane brace-to-chord angle (OPA) on the capacity of the multi-planar X-joints under OPBM. Moreover, the capacity under hogging moment is lower than that under sagging moment due to different load transfer mechanism. Then an extensive FE (verified by existing tests) parameters analyses are carried out to study the effect of OPA on the capacity, and an equation for the spatial effect factor is established. Furthermore, the effects of inplane brace-to-chord angle (IPA) on the capacity of the X-joints are also studied, and an additional incline factor is proposed to compensate for the underestimated effects of IPA on the capacity, which due to the current specification does not consider the favorable effect of the increasing brace/chord intersection area caused by inclined brace-chord. Finally, based on the existing specification applied to uniplanar CHS X-joints with the spatial factor and the incline factor, an improved specification is proposed and verified by FE results. And it predicts the capacity of the multi-planar X-joints with brace-to-chord diameter ratio larger than 0.6 better than the original specification.