Flexural behaviour of rectangular double-opening concrete filled sandwich steel tube (DCFSST) beams.

Experimental and numerical studies on flexural behaviour of rectangular double-opening concrete filled sandwich steel tube (DCFSST) beams were performed in this study. Six specimens under different cross-section of inner tube and nominal cross-sectional steel ratio (α n) were tested under bending to assess the failure modes, moment-displacement and moment-strain relationships, flexural capacity and flexural stiffness of rectangular DCFSST beams. The experimental results demonstrate that the two design variables investigated in this paper have limited impact on the failure modes of typical specimens. The failure mode of outer tube includes multiple local bulges on top flange and one case of fracture on bottom flange that is located at the same plane as the primary local bulge on top flange, whilst the failure mode of inner tubes is mainly due to excessive global deflection. Simultaneously, sandwich concrete is crushed at the locations with evident local bulge on outer tube and cracks nearly uniformly within the lower 2/3 section depth. In general, the flexural capacity and stiffness of the specimens enhance as α n increases, and are moderately affected by the cross-section of inner tube. In addition, finite element (FE) models were built to replicate the flexural behaviour of rectangular DCFSST beams, and the FE models were validated by comparison with test results. At the end of the paper, simplified formulae that can better predict the flexural capacity of rectangular DCFSST beams were developed. • Typical tests of rectangular DCFSST beams under bending were carried out. • FE models that can well reproduce the flexural behaviour of rectangular DCFSST beams were developed. • Formulae that can accurately predict the flexural capacity of rectangular DCFSST beams were proposed. [ABSTRACT FROM AUTHOR]