Flexural strength and stiffness of circular double-skin and double-tube concrete-filled steel tubes

Abstract

Circular double-skin and double-tube concrete-filled steel tubes (CFST) have become increasingly attractive especially in marine structures due to their favourable mechanical behaviour. With the development of (ultra) high strength materials, thin-walled and thick-walled steel structures, it is urgent to propose a design method suitable for a wider range of parameters. This paper develops fibre beam element (FBE) models for the circular double-skin and double-tube CFST members under pure bending. The FBE models are verified by the collected experimental results. Numerical data including 435 double-tube and 213 double-skin CFST beams are generated to cover extensive parameters. Based on the plastic-stress distribution method, the design formulae are deduced to calculate the flexural strength of circular double-skin and double-tube CFST members considering the different positions of neutral axis inside and outside the inner tube. The predicted results agree well with the FBE results and test results. Finally, the curvature from half-sine wave calculation is modified and the design method for flexural stiffness is proposed.