Design guidance for stainless steel, a material which is increasingly used in structural applications, has significantly improved in recent years. Yet, so far, not much attention has been paid to the behaviour of members submitted to torsion, in combination with bending or not. This paper presents a numerical study of duplex stainless steel welded I beams submitted to pure torsion. Firstly, a finite element model of a simply supported welded beam with a single concentrated torque applied at mid span is described. This model is validated against reference experiments. Since the observed behaviour of beams submitted to torsion is considerably different when their web is slender, different cross-section geometries are modelled to study the behaviour of both slender and non-slender webs. The analysis shows that, in beams with slender webs, local instability causes the beam to fail before the uniform strain is reached. Buckling of the web affects the behaviour of the flanges, causing the beam to fold rather than to rotate when submitted to torsion.
