Study on the brace axial force-local deformation behavior of unstiffened CHS X-joints

Numerical parametric analysis is carried out to study the force-local deformation (F-δ)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(F-\delta )$$\end{document} behavior of circular hollow section X-joints under brace axial force (including compression and tension) and chord stress. An exponential model is proposed to describe the F-δ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$F-\delta $$\end{document} curves of the X-joints. Parameters of the proposed model including two intercept forces and three joints stiffness (initial stiffness and two tangent stiffness) are determined by theoretical analysis, finite element (FE) analysis and nonlinear regression. The results show that the F-δ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$F-\delta $$\end{document} behavior under brace compression is significantly different from that of brace tension. Chord stress has little effect on the initial stiffness, but has a relatively large effect on the intercept forces and the tangent stiffness. The proposed model well predicts F-δ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$F-\delta $$\end{document} behavior of the X-joints from FE results, which including strength degradation caused by chord wall buckling.