Hence statistical coefficient is Kn = t95(n) / — + 1 = 1.742

Characteristic concrete strength is then X^ = mx - Knctx = 31.9 MPa ©

© Student's t-values are given in Figure 2.16.

© The statistical coefficient kn is based on (n - 1) degrees of freedom, the 'lost' degree of freedom being the standard deviation of the sample, which we have had to calculate.

© This is the 'inferior' characteristic value, which is the one most often needed in calculations of resistance.

© The standard deviation is based on an assumed coefficient of variation equal to 0.1.

© The statistical coefficient Kn is based on n degrees of freedom.

á The characteristic strength is slightly larger than that calculated at ©, since both the standard deviation and the statistical coefficient are smaller than before.

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