La variazione di schema statico nei ponti in cemento armato precompresso durante le fasi costruttive e l’influenza dei fenomeni lenti

The construction of prestressed concrete bridges often presents different construction stages in which the structural static scheme changes many times, together with the characteristics of the construction elements. In fact, prefabrication and in situ assembly involve a multiple variation of the scheme with the introduction and removal of restraints, especially when temporary sup-ports are used. These transitional phases can strongly modify the structural behavior, in relation also to the deformations due to shrinkage and creep. In this study an evaluation of the effects of time-dependent phenomena is presented, for the case of complex sequences in which delayed restraints and removal of provisional supports occur till the final configuration is achieved. The study is based on analytical methods and creep models available in the literature, discussing the implications on long-term behavior of bridges, both in terms of deformation and variation of the stress state. A practical application is also presented.