Adaptive Estimation of the In Situ Characteristic Concrete Strength

For calculation of existing concrete structures on the basis of the partial factor format, the main representative value is the actual in-situ characteristic value of the concrete strength. When samples are tested, the concrete in-situ strength of the structure shall be determined, statistically if possible, from the test results. In accordance with EN 1990 the 5% percentile value is calculated on the basis of a unilaterally limited constant confidence level. It was found the in some case, estimation of the in-situ characteristic concrete strength taking a constant confidence level does not allow to adequately assess the reliability of the existing structures. A new estimator based on non-parametric statistical method was proposed for estimating of the in-situ characteristic concrete strength with a given arbitrary confidence level. The procedure that was proposed allows one to re-establish of the estimator pdf even with a very limited sample size. It is established, that the choice of the confidence level of the estimator should be based on the average reliability of the structure.