Concrete-filled cold-formed circular steel tubes subjected to variable amplitude cyclic pure bending

This paper describes an experimental investigation of the cyclic inelastic flexural behaviour of concrete-filled tubes (CFT). Controlled-rotation, symmetrical cyclic bending tests were performed using a variable amplitude loading history on different sizes of CFT with different section slenderness. The CFT beams exhibited stable hysteresis behaviour up to local buckling and then showed considerable degradation in strength and ductility depending on the D/tD/t ratio. Seismic capacity parameters are presented including strength, hysteresis curves and modes of failure for the specimens. Peak moments obtained in the cyclic tests were compared with design moments predicted using a number of steel and concrete specifications. New section slenderness limits suitable for design and construction of seismic resisting structural systems were determined. A comparison is made between these seismic slenderness limits and the limits available in the design codes.