Research on mechanical behaviour of tapered concrete-filled double skin steel tubular members with large hollow ratio subjected to bending

Abstract

This paper reports a study on the mechanical behaviour of tapered concrete-filled double skin steel tubular (CFDST) members under bending. A total of twelve specimens with diverse hollow ratios and shear span ratios were tested. The failure mode, the distribution of the deflection curves, the bending moment-curvature curves (M-φ), the longitudinal stress distribution of the cross-section and the strain were investigated, respectively, to understand the bending performance and working mechanism of the specimens. Meanwhile, the finite element (FE) models of tapered CFDST members were developed to investigate the flexural behaviour by ABAQUS software. Finally, the calculation method for predicting the flexural capacity of tapered CFDST members was proposed. The results show that tapered CFDST specimen fails in a very ductile manner and no tensile fracture is observed at the tension region. The maximum deflection of tapered CFDST members occurs at the 3/4L0 section. Moreover, it is found that the flexural capacity is sensitive to the change of taper angle and hollow ratio due to the variation of flexure stiffness. For instance, ultimate bending capacity can be decreased by 62.6% when the taper angle changes from 0° to 1.71°. In addition, it is not reliable to directly select the minimum section of tapered CFDST members as designed section, which will underestimate the flexural capacity of the specimens. Therefore, the concept of equivalent section is proposed to predict the calculation, and the predicted results are satisfactorily in accordance with the measured results, which can provide certain reference for engineering design.