Seismic behavior and analytical model for a fully bolted joint between CFDST columns and steel beams

Abstract

A steel beam to concrete-filled double-skin steel tubular (CFDST) column joint was developed to improve the widespread use of CFDST columns in buildings. The comparative studies of six specimens under pseudo-static cyclic tests were designed and performed to examine the influence of endplate thickness, axial compression ratio, bolt diameter, concrete fill degree, and inner tube shape on the mechanical behavior of the joint. The failure modes were the bending of the endplate, warpage and fracture of bolts, fracture of the weld seam, and buckling of beam flanges. The displacement ductility coefficients exceeded 4.89, indicating that the connection had excellent ductility. Increasing the endplate thickness greatly improved the seismic indices of the joint. Although the higher axial compression ratio increased the bearing capacity and initial stiffness of the joint, the ductility and energy dissipation were unaffected. Improving the bolt diameter did not affect the bearing capacity, ductility, and energy dissipation capacity of the joint; however, it increased the initial stiffness and delayed the strength. The bearing capacity and initial stiffness of the joint were improved by increasing the concrete fill degree and using a square tube instead of the inner circular tube; however, it decreased the ductility and energy dissipation and accelerated the strength degradation of the joint. Finally, a calculation model of the initial rotational stiffness was proposed. The mean and standard deviation of the ratios of the predicted results to the experimental results were 0.95 and 0.14, respectively.