A new probabilsitic method to determine structural desing strengths from prototype load-testing has been developed specifically for Weibull strength distributions. The new probabilistic method has been evalauted and compared with a statistical prototype proof-loading method for Weibull strength distributions and iwth other probabilistic methods developed for Lognormal strength distributions. The methods have been evalauted and compared for Weibull-distributed strengths, with regard to statistics of the resultant design strengths, the associated safety indices beta, the nominal probabilities of failure and an entropy-based measure of overall uncertainty (accounting for the variability of the nominal probability of failure). The results confirm that the statistical procedure produces conservative design outcomes when it is based on conservative estimates of characteristic strength values, and the probabilistic procedure for Weibull-distributed strengths achieves a mean safety index close to the target value. However, it is shown that a probabilistic procedure developed for Lognormally-distributed strengths produces the most consistent results, even when the strengths are Weibull-distributed.
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