Evaluation of the plastic hinge length of steel-concrete composite beams under hogging moment

Lumped plasticity is one of the most commonly used approaches for the nonlinear analysis of framed structures, but its effectiveness depends on the reliability of the plastic rotational capacity. In the case of RC or steel structures, this approach is based on well-known and reliable formulations, but no specific rules have been established for steel-concrete composite structures. This paper reports the results of a detailed analysis of the nonlinear behaviour of the section and entire element of a composite beam with the goal of determining its flexural ductility. In particular, the composite beam was examined under a hogging moment that results in its worst performance due to the concrete experiencing tension and the steel compression. An FE model is used to study the element; it was considered all the features of the materials and the geometry of the section to develop a parametric analysis that enabled to study the effect of different parameters on the rotational capacities of the composite beams. This formulation considers the local phenomenon of profile buckling and the global dimensions of the composite section. Finally, the obtained results allowed to define an equivalent plastic hinge length that provides the available plastic rotation when multiplied by the plastic curvature of the cross-section.