Evaluación de flechas y estados tensodeformacionales en servicio, en puentes isostáticos de vigas prefabricadas de hormigón pretensado

Evaluation of deflections, stresses and strains at service in simply supported spliced precast prestressed concrete girder bridges

The verification of stresses, strains and deflections along the structural service life which is the basis of the design of prestressed concrete structures, becomes specially complex when dealing with bridges composed by precast prestressed concrete beams and a cast in place reinforced concrete slab. This is due to the time dependent stresses redistributions produced by the materials rheology and by segmental construction, even in statically, determinate bridge structures. Thus, in order to satisfy the serviceability limit states, the use of numerican models capable to simulate the above mentioned effects results of great interest. In this paper, a structural time dependent analysis model based on the principles of linear viscoelasticity, capable to accurately simulate the state of stresses, strains and deflections during the construction stage and along the structure service life, is presented. The model allows also to simulate load tests, the effects of temporary shoring of the beam and the segmental construction of the slab. The model has been implemented in a computer program adapted to personal computers, allowing by means of systematic use, to optimize the cross section dimensions, the amount of prestressing and mild reinforcements and the construction process. Two examples are presented to show the applicability of the program to analyse real simply supported composite concrete bridge structures. The obtained results have allowed to quantify the level of stresses, strains and deflections during construction and throughout the structure's service life; to evaluate the influence of several design and construction parameters, to show the importance of the stresses redistribution due to creep, shrinkage and relaxation and to evidence the difficulties of simplified formulations to predict the time dependent behaviour of such structures.