Permissible design values and variability test factors

Abstract

For the design of structural elements it is postulated that:- (a) not more than 10 per cent to any given design should have strength below the design value (b) not more than 0.1 per cent should have strength below 90 per cent of the design value. This rule forms a working basis for the interpretation of tests on statistical lines. On the basis of a fixed probability, Part I deduces:- (i) expressions for the derivation of permissible design values from a given number of test results (ii) the number of test results required, on specimens chosen at random, so that the estimates of permissible design values can be regarded as sufficiently accurate (iii) the factor which shouId be applied to the results of tests on any number of similar components designed to meet a specified requirement. The effects of different probabilities and of different acceptable proportions of weak specimens are investigated in Part II.