Stochastic Drying and Creep Effects in Concrete Structures

Abstract

The paper calculates how an aging concrete structure that has an uncertain constitutive law and random material properties responds to the random process of environmental humidity history. The time evolution of stochastic porehumidity distributions is solved from a linear diffusion equation. The stresses produced by the shrinkage strains are calculated taking concrete creep into account. The environmental humidity process is described by three components: one Poisson square‐wave random process and two random‐phase processes, having periods of one year and one day, the latter of which is found to have a negligible effect. The response to the random‐phase process is calculated by the spectral method combined with equal probability sampling. The Poisson‐process component is important for very long times since it produces a response whose standard deviation grows as the square root of time; the nonstationary random‐phase component stabilizes after about 10 years. The influence of the random‐phase process reaches a depth of about 20 cm below the concrete surface; that of the Poisson process reaches only about 5 cm. The randomness of the material parameters and the uncertainty factor of the material model influence the entire structure. A numerical example of a cylindrical wall is given and simplified explicit formulas for estimating the response statistics are derived.