THE ENGINEERING MECHANICS DIVISION STOCHASTIC PROCESS FOR EXTRAPOLATING CONCRETE CREEP

In the design of concrete structures for nuclear reactors, it has become standard practice to carry out creep tests of the particular concrete to be used. These tests are inevitably of limited duration, such as 6 months-12 months, and an extrapolation to the end of lifespan, usually 40 yr, is necessary (for an example of such a problem, see Fig. 3 of Ref. 7). Because of safety considerations, the designer is interested not merely in the expected value " of 4O-yr creep, but mainly in the extreme values that have a certain specified small probability (such as 5%) of being exceeded. Up until now most of the research has been concerned with trying to predict creep using deterministic models that best fit the data available in the literature. This has its merits as far as predicting the average behavior over long periods of time, but an estimate of the expected statistical variation is lacking. Its qualitative estimate can be obtained only by statistical means and this is going to be the prime concern of this paper. Literature on statistical treatment of creep of concrete is rather limited. Most of the work has dealt with creep in connection with long-term deflections o