Stress‐Induced Thermal and Shrinkage Strains in Concrete

Abstract

A previous material model for the increase of creep of concrete caused by simultaneous drying is extended to describe the effect of both drying and wetting, as well as the increase of creep caused by temperature changes, both heating and cooling. By theoretical arguments and comparisons with numerous existing test data, it is shown that the creep increase due to temperature changes, sometimes called the transitional thermal creep, is physically the same phenomenon as the increase of creep due to humidity changes, known as the Pickett effect (or the drying creep effect). In accord with the previous model for drying creep alone, the present extended model explains the increase of creep due to humidity or temperature changes as a consequence of principally two effects: (1) Stress‐induced shrinkage (or swelling) or stress‐induced thermal expansion (or contraction); and (2) the distributed tensile cracking (or strain‐softening) of concrete. The former effect is explained by the previously advanced hypothesis that the creep viscosity depends on the pore humidity rate. The latter effect reduces measured overall deformations, and thus results in the true thermal expansion or shrinkage of uncracked material being considerably larger than observed on load‐free companion specimens when significant nonuniformly distributed self‐equilibrated stresses are produced by the temperature or humidity change. The proposed material model is suitable for finite‐element programs.