An approximate solution for the rheological behavior of non-homogeneous structures changing the structural system during the construction process

Time-dependent phenomena as shrinkage and creep in concrete or relaxation in steel, deeply influence the stress and strain patterns of prestressed concrete bridges. Such phenomena are more relevant for staged-constructed bridges, in which a change of the static scheme occurs by the addition of restraints to the initial scheme. The aim of this paper is to develop an approximated procedure allowing to calculate the long-term stress and strain patterns in modern prestressed composite structures. The method is based on the introduction of a suitable number of time intervals depending on the constructive phases of the bridge; then, for each time step, the influence functions of the linear viscosity coefficient are defined together with the variation of this coefficient. The further introduction of the hypotheses of linear behavior of the viscous-elastic strain distribution and of external loads concentrated at the end of each time step, leads to a significant simplification of the problem presented above. The proposed calculation model is used to determine the stress–strain state of the “Quattroquerce Viaduct” located on the highway “A3” Salerno-Reggio Calabria, Italy.