Chord plastification in high strength steel circular hollow section X-joints: testing, modelling and strength predictions

This paper presents experimental and numerical investigations on cold-formed high strength steel (CFHSS) circular hollow section (CHS) X-joints. The CFHSS CHS members had nominal 0.2% proof stress up to 1100 MPa. The geometric parameters of the X-joints were designed by varying the ratios of β, 2γ and τ. Seventeen X-joint tests were conducted by applying axial compressive load through the braces without preloading in chords. Non-linear finite element model (FEM) was then developed for the CFHSS CHS X-joints. After successful validation of ultimate strengths, failure modes and load-deformation curves, parametric studies were performed by using the verified FEM. The chord plastification failure of the X-joints was mainly found in both test and numerical studies. The relationship between the joint strengths and the variation of geometric ratios were investigated. The strengths of the X-joints obtained in this study together with the test strengths collected from the literature were used to assess the strength predictions by CIDECT and EN-1993–1-8, as well as those from the literature. It was found that the current predictions generally provided unconservative predictions. A new equation that considers the effects of geometric ratios on the strengths was proposed based on both the test and numerical results. By adopting the newly proposed equation, the predictions are improved and provide the least scattered results when compared with the other predictions.