Análisis en el tiempo de estructuras masivas de hormigón mediante elementos finitos mixtos. Aplicación a las presas

Time-dependent analysis of massive concrete structures using mixed finite elements. Applications to dams

Massive concrete structures, and particularly concrete dams, suffer delayed deformations in all directions, due to shrinkage and creep, which normally generate stresses. Besides during their construction process (in general implying changes in structural configuration and additional stress redistributions) creep and shrinkage are important and interact with heat of hydratation. Normally, all these effects are not negligible and must be consifered for design and construction, trying to prevent concrete cracking. In this work, a general procedure for 3 dimensional (3-D) time-dependent analysis of creep and shrinkage is proposed. Creep and shrinkage deformations are taken as geometrical actions and so, considered out of the material model itself. Mixed finite elemnts, based on the Reissner functional are employed. This aspects have important advantafes, implying an efficient procedure. Two approaches of concrete creep, consisting of extrapolations of one-dimensional creep behaviour to 3-D have been adopted (one is directly expressed in strains and the other in stresses). Several theoretical properties, very interesting for the prevision of certain practical results, have also been studied. For evaluating the procedure and its precission, as well as the structural differences when taking one creep approach or another, two examples have been presented: a simple beam, dealt both in 3-D by the proposed approach and in 1-D by the classical beam solution (validation of the procedure) and a block (comparison at 3-D structural level between both crep options). The results from various examples show to be very consistent and percise, according very well with theoretical precisions and with the beam solution. Results for the concrete block using both creep approaches are, in general, rather simuilar, but differences in stresses can be locally strong, what is significant, facing the precission of concrete cracking.