Moment Redistribution in Steel-Concrete Composite Beams at Ultimate Limit State

The paper investigates the design of continuous steel-concrete composite beams using the elastic analysis with limited redistribution. The permissible moment redistribution which satisfies the requirements of the ultimate limit state (ULS) was computed. An advanced finite element program accounting for all mechanical nonlinearities was used. An extensive parametric analysis aimed to determine the influence of several geometrical parameters on the permissible moment redistribution was carried out on propped cantilevers. The analyzed parameters include the shape of the steel profile, the ratio between the depths of the concrete slab and of the steel beam, the steel to concrete area ratio and the reinforcement percentage of the concrete slab. The analysis was limited to compact steel sections (class 1 in accordance with the Eurocode 3) and low ductility reinforcing steel (characteristic elongation at maximum load 2.5%). A moment redistribution lower than that recommended by Eurocode 4 was found for high values of the reinforcement to steel area ratio due to limited rotation capacity at ULS.