Designing for torsion in open-section steel members

• Autores: Richard Henderson
• Localización: The Structural Engineer: journal of the Institution of Structural Engineer, ISSN 1466-5123, Vol. 101, Nº. 7, 2023, págs. 28-33
• Idioma: inglés
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• Resumen

  • The purpose of this Technical Guidance Note is to assist structural engineers familiar with the theoretical behaviour of steel structural elements subject to torsion to avoid or design for it when necessary.

    The note will: | briefly describe the behaviour of open sections when subject to torsion | discuss the treatment of resistance to torsion in BS EN 1993-1-1 (EC3) | consider serviceability of elements affected by torsion | examine resistance to torsion with an illustrative example.

    Circular tubes, which are an example of a closed section, are particularly efficient at resisting torsion. Open sections, such as I-profiles, channels and angles, are unsuited to resisting torsion because, in doing so, they twist too much and also develop axial stresses which reduce their bending resistance. In general, managing twist will be the governing design criterion.

    It is suggested that designers avoid torsion in members wherever possible by adopting suitable framing arrangements. If torsion is unavoidable, e.g. in beams curved on plan, rectangular hollow sections are a better choice of member. However, torsion may be unavoidable as a temporary condition during construction. It may also be necessary to assess torsion on open sections when appraising or modifying existing structures.