Section Classification & b/t Limits for Hollow Sections


Most of the current b/t limitations in international steel design standards are based on investigations of hot-rolled I-sections. This project has been examining the behaviour of hollow sections, such as RHS and SHS to examine their classifications.To date, there have been bending only tests on SHS and RHS, as well as bending and compression tests on SHS and RHS in both the Class 1 and Class 2 range. Finite element simulation has also been performed.


Associate Professor Tim Wilkinson

Research Location

Civil Engineering

Program Type



When a beam has suitable lateral bracing, its strength is usually governed by local buckling of the individual plate elements that make up the cross-section. A section is classified according to its moment capacity with respect to the fully plastic moment (Mp) and the yield moment (My) and the rotation capacity. A beam cross-section that can resist the plastic moment, and has a sufficiently large rotation capacity to be deemed suitable for plastic design is sometimes call a “Class 1” or “plastic” or “compact” section depending on the terminology of the relevant specification.

Local buckling is primarily a function of the slenderness of the individual plate elements, usually referred to as the b/t ratio. Design standards specify slenderness limits against which the b/t values are compared in order to classify a cross-section. These limits change according to the stress distribution and support conditions experienced by the element under consideration. Some of the publications related to this research include:

*Wilkinson T. and Hancock G. J., (2002), “Predicting the rotation capacity of cold-formed RHS beams using finite element analysis”, Journal of Constructional Steel Research, Elsevier, Vol 58, No 11, November 2002, pp 1455 - 1471.

*Wilkinson T. and Hancock G. J., (2000), “Tests to examine plastic behavior of knee joints in cold formed RHS”, Journal of Structural Engineering, American Society of Civil Engineers, Vol 126, No 3, March 2000, pp 297 305.

*Wilkinson T., (2003), “Recommendations for Cold-Formed RHS in Bending and Compression”, Tubular Structures X, Proceedings of the 10th International Symposium on Tubular Structures, Madrid Spain, (Balkema, publ.), (Jaurrieta, Alonso & Chica eds.), pp 293 300.

*Wood K. and Wilkinson T., (2003), “Measuring Imperfections in Hollow Sections”, Tubular Structures X, Proceedings of the 10th International Symposium on Tubular Structures, Madrid Spain, (Balkema, publ.), (Jaurrieta, Alonso & Chica eds.), pp 285-292

*Jouaux R & Wilkinson T, (2005), "Tests To Examine The Effect Of Axial Compression On The Rotation Capacity Of Square Hollow Sections", ICASS05, 5th International Conference on Advances in Steel Structures, Shanghai, China

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structural engineering, section classfication, hollow sections

Opportunity ID

The opportunity ID for this research opportunity is: 417

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