Design of cold-formed high strength steel tubular T-joints under compression loads

This study presents a comprehensive finite element (FE) analysis of cold-formed high strength steel (CFHSS) tubular T-joints. The brace members of tubular T-joints were made up of rectangular (including square) and circular hollow sections (RHS and CHS), whereas the chord members were made up of RHS. The nominal yield strengths (i.e. 0.2% proof stresses) of the tubular members were 900 and 960 MPa for S900 and S960 steels, respectively. Finite element (FE) models were developed and verified against the tests conducted by Pandey and Young (2019), showing the capability of reciprocating the experimental joint strengths, failure modes and load-deformation histories. The material properties and test results used for the validations of the FE models are reported in Pandey and Young (2019). The tubular T-joints were tested under axial compression through the brace members, while the ends of the chord members were supported on rollers. Upon validations of the FE models, a parametric study comprised of 285 FE analyses was carried out. The validity ranges of governing parameters in this study exceeded the current validity ranges given in the EC3 (EN 1993-1-8, 2005) and CIDECT (Packer et al., 2009). A total of 309 joint strengths obtained from the tests (Pandey and Young, 2019) and parametric study were compared with the nominal strengths obtained from the EC3 (EN 1993-1-8, 2005) and CIDECT (Packer et al., 2009). In this study, three failure modes were observed, namely chord face failure, chord side wall failure and combined failure. The applicability of current chord stress function given in the CIDECT (Packer et al., 2009) was also evaluated for cold-formed tubular T-joints of S900 and S960 steel grades. It is shown that the existing design rules given in the EC3 (EN 1993-1-8, 2005) and CIDECT (Packer et al., 2009) are not directly suitable for T-joints of S900 and S960 steels with validity ranges of governing parameters exceeding the limits specified in these specifications (EN 1993-1-8, 2005, Packer et al., 2009) and their modifications are needed. Therefore, using two approaches, i.e. semi-empirical and by applying correction factors on the latest equations given in the EC3 (EN 1993-1-8, 2005, EN 1993-1-12, 2007), design rules are proposed in this study for cold-formed tubular T-joints of S900 and S960 steel grades. In addition, reliability analyses were also performed to check the reliability levels of the existing and proposed design rules.