Cyclic bending tests to determine fully ductile section slenderness limits for cold-formed circular hollow sections

This paper determines new section slenderness limits suitable for design and construction of seismic resisting structural systems. It describes an experimental investigation of the cyclic inelastic flexural behavior of cold-formed circular hollow section (CHS) beams. Controlled-rotation, symmetrical cyclic bending tests were performed on different sizes compact CHS with section slenderness Dit ranging from 13 to 39. With continuous cycling, the growth of ovalization caused a progressive reduction in the bending rigidity of the tube and eventually an instability occurred. The CHS beams exhibited stable hysteresis behavior up to local buckling and then showed considerable degradation in strength and ductility depending upon the Dit ratio. Seismic capacity parameters are presented, including strength, stiffness, hysteresis loops and modes of failure for each specimen. Peak moments obtained in the cyclic tests were compared with those obtained in monotonic tests published previously and also with design moments predicted using a number of steel specifications. The deformation ductility demand was determined and used to derive new fully ductile section slenderness limits suitable for seismic design. A comparison is made between these seismic slenderness limits and the static limits available in the design codes.