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 26 the stress and strain patterns of prestressed concrete bridges. Such phenomena are more relevant for 27 staged-constructed bridges, in which a change of the static scheme occurs by the addition of restraints 28 to the initial scheme. The aim of this paper is to develop an approximated procedure allowing to calculate 29 the long-term stress and strain patterns in modern prestressed composite structures. The method is 30 based on the introduction of a suitable number of time intervals depending on the constructive phases 31 of the bridge; then, for each time step, the influence functions of the linear viscosity coefficient are 32 defined together with the variation of this coefficient. The further introduction of the hypotheses of linear 33 behavior of the viscous-elastic strain distribution and the external loads concentrated at the end of each 34 time step, leads to a significant simplification of the problem presented above. The proposed calculation 35 model is used to determine the stress–strain state of the ‘‘Quattroquerce Viaduct’’ located on the highway 36 ‘‘A3’’ Salerno-Reggio Calabria, Italy.