Time dependent behaviour of continuous composite beams: comparison between different prestressing techniques

The long-term behaviour of continuous steel-concrete composite beams is investigated to evaluate the effectiveness of the principal prestressing systems generally used to prevent concrete cracking in the regions of the internal supports. Four prestressing techniques are considered: the first with imposed support settlements, the second with internal cables in cast-in-situ slab, the third with internal cables in precast concrete slab and the fourth with external cables. The time-evolution of the compressive stress on the slab is studied evaluating the magnitude of the stress loss due to the concrete creep. The study is carried out on a composite beam model with flexible shear connection which permits taking into account the slip at the beam-slab interface and calculating the longitudinal shear force distribution which is particularly important at the cable anchorage sections