Bending tests to determine slenderness limits for cold-formed circular hollow sections

There are significant differences in slenderness limits recommended in various codes for circular hollow sections (CHS) under bending as there have been little experimental studies. In this paper an attempt is made to establish more accurate slenderness limits for cold-formed circular hollow sections. This paper describes a series of bending tests to examine the influence of section slenderness on the inelastic bending properties of cold-formed CHS. Twelve bending tests were performed up to failure on different sizes of CHS with diameter-to-thickness ratio d/t ranging from 37 to 122. This range of d/t was obtained by machining as-received cold-formed circular hollow sections grade C350L0. The test results are compared with other experimental data and the design rules given in various steel specifications. The slenderness limits were established to define Class 1 (compact), 2, 3 (non-compact) and 4 (slender). These limits were based on modifications of criteria for rotation capacity commonly used for steel structures. A design curve was developed and recommended for the design of cold-formed CHS under pure bending.