Duration of Load Tests for Dry Lumber in Bending: A Comment

The validity of the presently employed duration-of-load concept has been challenged by Madsen in a recent article. His questioning of some long-held beliefs is well motivated, and he deserves much credit for his attempt to shake what are quite possibly faulty foundations. A critical limitation of his methods of handling data, however, shows that the matter must be regarded as unresolved. To estimate various percentiles, Madsen has plotted failing loads against “normalized” ranks for several loading rates, and made polynomial fits to the resulting points in each case. The normalized ranks were designed as a measure of the percentage of the population failing up to a certain load, in other words, an estimate of the cumulative distribution function F.00. If x1

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