Non-parametric evaluation of the characteristic in-situ concrete compressive strength

Currently, CEN TC/250 completes the development of a new generation of Structural Eurocodes. In accordance with the strategy declared in Mandate M/515 EN, each Eurocode should contain special requirements related to the assessment and retrofitting of existing structures. The characteristic in-situ concrete strength can be statistically determined based on test results. According to draft EN 13791, the 5-th-percentile value can be calculated based on a unilaterally limited constant of 75% confidence level. Sometimes, estimation of the characteristic in-situ concrete strength based on a constant confidence level does not allow for an adequate reliability assessment of existing structures. Therefore a new estimator based on non-parametric statistics has been proposed for estimating the in-situ characteristic concrete strength with a given arbitrary confidence level. It was found that the choice of confidence level estimation should be based on the average level of structural reliability (ALSR).