INELASTIC NONUNIFORM TORSION OF STEEL I-BEAMS

This paper presents a finite element model for analysing the elastic-plastic nonuniform torsion behaviour of thin-walled steel I-beams. The model uses Vlasov's warping strain model to represent warping torsion, and a mitre model for uniform torsion. The mitre model allows the representation at the tips of flanges of the transverse uniform torsion shear stresses. For elastic-plastic analysis, the incremental theory of plasticity is adopted, employing the Prandtl-Reuss flow rule and the von Mises yield criterion. The material state determination algorithm and the variable arc-length method are also employed to improve the accuracy and reliability of the solutions. The numerical integration over the cross-section is carried out by dividing it into a number of triangular areas and then applying the no-bias area-coordinate Gaussian numerical integration scheme. The numerical examples provided show that good agreement is obtained with predictions of other models of inelastic nonuniform torsion and the experimental results by using the present finite element model. It is also concluded that the present model can predict more realistic results at higher rotations than other models which ignore the transverse uniform torsion shear stresses.