Concrete material has time-dependent properties, namely creep and shrinkage, which induce the long-term deformation in concrete structures. The long-term behavior may cause the concrete cracking and the deterioration of serviceability and durability. Therefore, the effect of the long-term behavior obtained from the prediction should be considered in the process of design and construction.
Most research and prediction models on creep of concrete have been concerned with the uniaxial stress state. Research on creep under multiaxial stresses, however, has been relatively scarce, and the properties of creep under multiaxial stresses have not been fully understood even though concrete is subjected to multiaxial stresses in many structural members and structures.
The Poisson’s ratio due to multiaxial creep of concrete that has been reported by some experimental works is very controversial. When calculated from measured strains, Poisson’s 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 precisely understand the properties of multiaxial creep of concrete, a new approach method is needed.
Therefore, to definitely find out the properties of creep under multiaxial stresses, elaborate experimental study and analytical study using microplane model as a new approach method are preformed in this study. In addition to these experimental and analytical studies, numerical analyses are carried out for CFT column as a representative concrete member being under multiaxial stresses, the effect of the found creep properties on structural response is investigated.
Twenty-seven specimens for three concrete mixes were tested for basic creep under constantly sustained multiaxial stresses. From the experiments, it was found that volumetric and deviatoric creep strains are linearly proportional to volumetric and deviator...