Analytical studies on creep of sealed concrete under multiaxial stresses using a microplane model

Abstract

The Poisson ratio resulting from multiaxial creep of concrete, which has been reported by some experimental works, is controversial. When calculated from measured strains, Poisson ratio is very sensitive to small experimental error. This sensitivity makes it difficult to determine whether the ratio varies with time or remains constant, and whether it has a different value with stress states. To understand precisely the properties of multiaxial creep of concrete, a new approach is needed. In this study, microplane model is applied to optimally fitting test data extracted from experimental studies on multiaxial creep of concrete. Double-power law is used as a model to represent volumetric and deviatoric creep evolutions on a microplane. Six parameters representing the volumetric and deviatoric compliance functions are determined from regression analysis, and the optimum fits accurately simulate the test data. Poisson ratio is calculated from the optimum fits and its value varies with time. Regression analysis is also performed on the assumption that multiaxial creep of concrete is isotropic. Four parameters are determined for this condition, and the error between the optimum fits and the test data is slightly larger than that for the six-parameter regression results. The constant Poisson ratio with time is obtained from the results of the four-parameter analysis, and the constant value can be used in practice without serious error.