Torsional behavior of I-steel-concrete composite beam considering the composite effects

To investigate the mechanical behavior of composite beams under pure torsion, considering the torsional contribution of the steel beam flanges, we established finite element models of I-steel-concrete composite beams. The nonlinear material constitutive relationship of concrete and steel was adopted in the model, and we validated the relationship by tests. Afterward, parametric analyses were carried out to study the main factors affecting the torsional performance of the composite beam. Our primary investigation focused on the composite effects and load sharing ratio of the steel beam and the concrete slab under pure torsion. We established the formulas for obtaining the maximum shear stresses in the concrete slab and the steel beam based on the composite effects and superposition principle. From these tests and our calculations, we proposed a model defining the torsional bearing capacity and the torsional stiffness of the I-steel-concrete composite beam; thus, the torsional contribution of the concrete slab and the steel beam were a primary concern in this research. Bearing capacity formulas are also proposed herein and are comparable with those in the literature, demonstrating that our formulas, with simple forms, are highly reliable when predicting the torsional behavior of the composite beam.