Análisis en el tiempo de puentes continuos de hormigón construidos a partir de elementos prefabricados

Time-dependent analysis of continuous span concrete bridges made up of precast elements

Actual time-dependent analysis can hardly be avoided in envolving concrete structures, because of the generally relevant effects of the delayed properties of concrete, creep and shrinkage. Changes in structural configuration, together with creep and shrinkage, cause delayed compatibility effects (that, in general, are not negligible) when passing from one stage to another. A new technology of bridges has began to be used in Spain. These bridges, composed of precast prestressed and reinforced concrete elements, and cast-in-place concrete deck slab, are made continuous later; because of the joints are placed at the span areas, they can reach longer spans than usual. Their double evolution, until reaching the final structural configuration, justifies a rather accurate analysis of the delayed effects. This work presents a general procedure for the time-dependent analysis of concrete structures subjected to longitudinal and transversal evolution. The procedure is based on a time discretization process in which creep and shrinkage are taken as geometrical actions, and influence lines for them are employed. The effects of active (with relaxation) and passive steel, and the cracking of concrete at some areas, are taken into account; as well, structural serviceability conditions are assumed under permanent loads, those involving creep. This general procedure is applied lattor to the aforementioned bridges, considering several options for the construction system (depending on the real sequence of the operations involved), different concretes in slab and precast elements (and different concrete ages), etc., with interesting results from a real example and a comparison with others derived from analytical approaches, for validating the procedure, are also included. Finally, some conclusions from the analysis procedure and its developments, as well as from its application to these bridges and the practical results obtained, are pointed out.