Creep analysis of structures with variable statistical scheme-unified approach

Variation of statistical scheme of reinforced and prestressed concrete structures is frequent in modem construction techniques. Construction sequences may include application of permanent loads and of prestressing in one or more steps, and connection of different portions of the structure, or introduction of additional restraints (sometime forcedly applied to correct the intemal stress conditions), at different ages during or after the construction process. The resulting stress distribution is largely influenced by the time-dependent deformability of concrete. The paper presents a unified approach for its evaluation based on the linear theory of viscoelasticity for aging materials, which is normally adopted for modeling concrete creep, evidencing the important role played by the non-dimensional redistribution function (1.111 t) describing the creep induced stress variation at timet for loading at 10 and variation of restraint conditions at t r The obtained solutions are exact for all problems of variation of restraint conditions in homogeneous structures with rigid restraints, and normally sufficiently accurate for problems concerning structures characterized by heterogeneities in the properties of concrete along their structural configuration. Redistribution function may be computed from the creep function J characterizing the creep prediction model under consideration and made available in tem1s of design aids (graphs or tables). The computational procedure is illustrated and an example of application to a typical structural problem is presented.