Fts

38.6 MPa

The standard deviation is Sx

which can also be calculated using Sx =

The coefficient of variation is VX =-= 0.118

X mX

Minimum coefficient of variation is 0.1, hence: VX = max (VX, 0.1) = 0.118 ©

With no prior knowledge of concrete strength (variance unknown) Student's t-value for 95% confidence limit with (n - 1) degrees of freedom is t95(n - 1) = 1.711 ©

Hence statistical coefficient is kn = t95(n - 1) / — + 1 = 1.745 ©

Characteristic concrete strength is then Xk = mx - k^x = 30.6 MPa ©

With prior knowledge of concrete strength (variance known)

Assume coeff. of variation is &x = 0.1 and mean value mx = mX = 38.6 MPa

Student's t-value for 95% confidence limit with n degrees of freedom is t95(n) = 1.708 ©

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