Early-age shrinkage and slab casting sequences in a long steel-concrete composite viaduct

This paper presents a study on the effectiveness of different casting sequences to control the cracking tendency in a long continuous steel-concrete composite viaduct. The main features of the early-age behaviour of concretes are addressed and the relative modelling options are discussed. The results of previous researches are recalled pointing out the influence of the bridge span-length, and the effects of tensile creep on the tensile stress state of bridges with few spans. Then, the application to a real viaduct with 12 spans of different length is presented. The continuous sequence and two fractionated sequences of casting are considered. The importance of the choice of segments in which the slab is subdivided during the casting is pointed out. Effects of thermal shrinkage confirmed to be the main cause of cracking together with those due to the weight of new segments. The enhanced creep of concrete in tension may reduce stress states below the concrete tensile strength even in the long term since the stresses due to the development of the drying shrinkage are compensated by the relaxation of stresses due to the early-age concrete and to the weight of the slab.