Behaviour of Composite Bridges during Construction

The behaviour of steel-concrete composite bridges is influenced by time-dependent effects in the concrete deck slab that can affect the durability of such structures. A detailed study of the causes of transverse cracking in concrete slabs of composite bridges has been carried out to understand better the origin of tensile stresses in the slab. In situ measurements and laboratory tests have enabled the behaviour of concrete slabs to be observed from the moment they were placed. The results demonstrate the important influence of concrete hydration and the pouring sequence on the tensile stresses in the slab. It is shown that for typical bridges the most critical tensile stresses in the slab are induced during construction. Methods for limiting the effects of hydration have been tested and the results compared with those of numerical simulations. A criterion for evaluating the probability of crack formation in young concrete has been established based on these simulations.