Fire resistance of restrained circular concrete-filled double-skin steel tubular columns

In the past decade, more and more attention has been paid to the fire performance of concrete-filled double-skin steel tubular (CFDST) columns. The columns in actual structures are not isolated members and are affected by the adjacent structural members. However, little research has been conducted on the behaviour of restrained CFDST columns under fire. In this paper finite element models were developed to analyse the fire performance of axially and rotationally restrained circular CFDST columns. The predicted temperature-time curves, internal axial force-time curves and fire resistance agreed well with the related test results. Based on the verified models, a parametric study was performed to investigate the effect on the internal axial force-time curves and fire resistance. The parameters included axial load level, axial restraint ratio, diameter of the outer tube, slenderness ratio, diameter-to-thickness ratios of the outer and inner steel tubes, dimension ratio of the inner tube to the outer tube, load eccentricity, yield strengths of the outer and inner tubes, compressive strength of the concrete, fire protection thickness and rotational restraint ratio. Through regression analysis, a design formula was proposed to calculate the fire resistance of restrained circular CFDST columns.