Random Shrinkage Stresses in Aging Viscoelastic Vessel

Shrinkage stresses caused by random variation of environmental humidity in a long cylindrical concrete wall sealed at the internal surface are analyzed, taking creep and aging of concrete into account. The random time-variation of humidity and stress is analyzed by the spectral method using the elastic-viscoelastic analogy. Spatial variations are described by Bessel and Kelvin functions. Numerical examples typical of a 1 m thick reactor containment and a thin shell of 10 cm thickness are given. The environmental humidity varies with a dominant period of one year. The results confirm that, due to low moisture diffusivity, as well as aging, the problem must be analyzed as nonstationary. The mean and the standard deviation are obtained as functions of time as well as location. Random stress fluctuations are found to be significant in all cases and the influence of aging to be strong. In the thicker containment only about 30 percent of the wall thickness ever feels the random variation, while in the thin shell the entire thickness is affected.