Abstract
In past many analytical studies on the creep stress in concrete structures and structural elements two hypotheses of proportionality of creep strain to stress and superposition of creep strain has been used for expressing the creep strain of plain concrete. However, recent researches indicate that these classic hypotheses do not always give exact time-creep strain relationship. That is, recently it has been cleared that the creep strain consists of two parts, i. e. , delayed elastic strain and flow strain, and the former recovers completely after applied stress is removed. In addition, time-delayed elastic strain relationship has no relation with the age of load-apply and same curve can be observed without regard to the age of load apply, although classic hypotheses can be applied to the expression of time-flow strain relationship. In this study, basing on recent experimental knowledges on the creep of plain concrete, time-creep strain relationship has been expressed in dividing into delayed elastic strain, flow strain and strain recovery for applying to the creep stress analysis of concrete structures and structural members. The expressions have been applied to the analysis of prestress loss in prestressed concrete beam and the effect of creep recovery upon the prestress loss has been discussed basing on the numerical examples. And further, comparison between the numerical results of prestress loss basing on the proposed creep strain expression and those oh classic hypotheses was made on the prestressed concrete beam. As the conclusion, followings were obtained: (1) The effect of the creep recovery upon the creep stress analysis is so small as negligible and it is no necessary to consider the creep recovery in the practical analysis of creep effect. (2) Creep stress analysis basing on classic hypotheses gives conservative result compared with that on recent creep hypotheses proposed in this study.
