Design of concrete-filled high strength steel tubular X-joints subjected to compression

Abstract

The structural performance and design of concrete-filled high strength steel tubular X-joints subjected to compression are investigated. A numerical investigation on the behaviour of concrete-filled high strength steel tubular chord members under concentrated bearing load has been performed. The high strength steel tubes had nominal yield stresses of 700 and 900 MPa. The infilled concrete had nominal concrete cylinder strengths of 35 and 100 MPa. In order to avoid the failure of brace members and reveal the true capacity of the X-joints, steel bearing plates were used to simulate the brace members. A finite element model was developed and validated against test results. Furthermore, a parametric study comprised 156 finite element analyses was carried out. The strengths of the concrete-filled high strength steel square and rectangular hollow section X-joints obtained from the parametric study together with available data in the literature were compared with the nominal strengths calculated from the CIDECT Design Guide. It is shown that the CIDECT design predictions exhibit significant scatter and could be unconservative for the concrete-filled tubular joints with chord sidewall slenderness ratio beyond 40 in this study. Hence, new design rules are proposed for concrete-filled high strength steel tubular X-joints subjected to compression. It is shown that the proposed design rules are able to provide reasonably good predictions.