Nonlinear analysis of composite beams subjected to combined flexure and torsion

There are situations in which a composite steel-concrete beam is subjected to torsion, such as members that are curved in plan or straight edge beams in buildings or bridges. The composite action of the steel beam and concrete slab in torsion is usually ignored in design codes of practice. Therefore, a three-dimensional (3D) finite element model is introduced in this paper to simulate composite steel-concrete beams subjected to combined flexure and torsion with the influence of partial shear connection using a commercial software ABAQUS. Brick and truss elements were used with the incorporation of nonlinear material characteristics and geometric behaviour in the model. This is coupled with an extensive parametric study using the validated finite element model using different parameters such as the span length and the level of shear connection. From the analytical study, a new phenomenon has been uncovered, which was validated by the test observation. This phenomenon called torsion induced vertical slip is an important issue, which would make the assumption plane sections remain plane invalid. In addition, difference in span length greatly affected the flexure-torsion interaction relationship of the composite steel-concrete beams, whilst the partial shear connection did not affect the relationship. Design models for readers to take away at the end of this paper are also proposed.